// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);
    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);
    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);
    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);
    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);
    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);
    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import {IERC20} from "./IERC20.sol";
interface IERC20Detailed is IERC20 {
    function name() external view returns(string memory);
    function symbol() external view returns(string memory);
    function decimals() external view returns(uint8);
}
// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
interface ITransferHook {
    function onTransfer(address from, address to, uint256 amount) external;
}pragma solidity ^0.6.2;
/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }
    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");
        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}pragma solidity ^0.6.0;
import './UpgradeabilityProxy.sol';
/**
 * @title BaseAdminUpgradeabilityProxy
 * @dev This contract combines an upgradeability proxy with an authorization
 * mechanism for administrative tasks.
 * All external functions in this contract must be guarded by the
 * `ifAdmin` modifier. See ethereum/solidity#3864 for a Solidity
 * feature proposal that would enable this to be done automatically.
 */
contract BaseAdminUpgradeabilityProxy is BaseUpgradeabilityProxy {
  /**
   * @dev Emitted when the administration has been transferred.
   * @param previousAdmin Address of the previous admin.
   * @param newAdmin Address of the new admin.
   */
  event AdminChanged(address previousAdmin, address newAdmin);
  /**
   * @dev Storage slot with the admin of the contract.
   * This is the keccak-256 hash of "eip1967.proxy.admin" subtracted by 1, and is
   * validated in the constructor.
   */
  bytes32 internal constant ADMIN_SLOT = 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103;
  /**
   * @dev Modifier to check whether the `msg.sender` is the admin.
   * If it is, it will run the function. Otherwise, it will delegate the call
   * to the implementation.
   */
  modifier ifAdmin() {
    if (msg.sender == _admin()) {
      _;
    } else {
      _fallback();
    }
  }
  /**
   * @return The address of the proxy admin.
   */
  function admin() external ifAdmin returns (address) {
    return _admin();
  }
  /**
   * @return The address of the implementation.
   */
  function implementation() external ifAdmin returns (address) {
    return _implementation();
  }
  /**
   * @dev Changes the admin of the proxy.
   * Only the current admin can call this function.
   * @param newAdmin Address to transfer proxy administration to.
   */
  function changeAdmin(address newAdmin) external ifAdmin {
    require(newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");
    emit AdminChanged(_admin(), newAdmin);
    _setAdmin(newAdmin);
  }
  /**
   * @dev Upgrade the backing implementation of the proxy.
   * Only the admin can call this function.
   * @param newImplementation Address of the new implementation.
   */
  function upgradeTo(address newImplementation) external ifAdmin {
    _upgradeTo(newImplementation);
  }
  /**
   * @dev Upgrade the backing implementation of the proxy and call a function
   * on the new implementation.
   * This is useful to initialize the proxied contract.
   * @param newImplementation Address of the new implementation.
   * @param data Data to send as msg.data in the low level call.
   * It should include the signature and the parameters of the function to be called, as described in
   * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
   */
  function upgradeToAndCall(address newImplementation, bytes calldata data) payable external ifAdmin {
    _upgradeTo(newImplementation);
    (bool success,) = newImplementation.delegatecall(data);
    require(success);
  }
  /**
   * @return adm The admin slot.
   */
  function _admin() internal view returns (address adm) {
    bytes32 slot = ADMIN_SLOT;
    assembly {
      adm := sload(slot)
    }
  }
  /**
   * @dev Sets the address of the proxy admin.
   * @param newAdmin Address of the new proxy admin.
   */
  function _setAdmin(address newAdmin) internal {
    bytes32 slot = ADMIN_SLOT;
    assembly {
      sstore(slot, newAdmin)
    }
  }
  /**
   * @dev Only fall back when the sender is not the admin.
   */
  function _willFallback() internal override virtual {
    require(msg.sender != _admin(), "Cannot call fallback function from the proxy admin");
    super._willFallback();
  }
}pragma solidity ^0.6.0;
import './BaseUpgradeabilityProxy.sol';
/**
 * @title UpgradeabilityProxy
 * @dev Extends BaseUpgradeabilityProxy with a constructor for initializing
 * implementation and init data.
 */
contract UpgradeabilityProxy is BaseUpgradeabilityProxy {
  /**
   * @dev Contract constructor.
   * @param _logic Address of the initial implementation.
   * @param _data Data to send as msg.data to the implementation to initialize the proxied contract.
   * It should include the signature and the parameters of the function to be called, as described in
   * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
   * This parameter is optional, if no data is given the initialization call to proxied contract will be skipped.
   */
  constructor(address _logic, bytes memory _data) public payable {
    assert(IMPLEMENTATION_SLOT == bytes32(uint256(keccak256('eip1967.proxy.implementation')) - 1));
    _setImplementation(_logic);
    if(_data.length > 0) {
      (bool success,) = _logic.delegatecall(_data);
      require(success);
    }
  }  
}pragma solidity ^0.6.0;
import './Proxy.sol';
import './Address.sol';
/**
 * @title BaseUpgradeabilityProxy
 * @dev This contract implements a proxy that allows to change the
 * implementation address to which it will delegate.
 * Such a change is called an implementation upgrade.
 */
contract BaseUpgradeabilityProxy is Proxy {
  /**
   * @dev Emitted when the implementation is upgraded.
   * @param implementation Address of the new implementation.
   */
  event Upgraded(address indexed implementation);
  /**
   * @dev Storage slot with the address of the current implementation.
   * This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1, and is
   * validated in the constructor.
   */
  bytes32 internal constant IMPLEMENTATION_SLOT = 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
  /**
   * @dev Returns the current implementation.
   * @return impl Address of the current implementation
   */
  function _implementation() internal override view returns (address impl) {
    bytes32 slot = IMPLEMENTATION_SLOT;
    assembly {
      impl := sload(slot)
    }
  }
  /**
   * @dev Upgrades the proxy to a new implementation.
   * @param newImplementation Address of the new implementation.
   */
  function _upgradeTo(address newImplementation) internal {
    _setImplementation(newImplementation);
    emit Upgraded(newImplementation);
  }
  /**
   * @dev Sets the implementation address of the proxy.
   * @param newImplementation Address of the new implementation.
   */
  function _setImplementation(address newImplementation) internal {
    require(Address.isContract(newImplementation), "Cannot set a proxy implementation to a non-contract address");
    bytes32 slot = IMPLEMENTATION_SLOT;
    assembly {
      sstore(slot, newImplementation)
    }
  }
}pragma solidity ^0.6.0;
/**
 * @title Proxy
 * @dev Implements delegation of calls to other contracts, with proper
 * forwarding of return values and bubbling of failures.
 * It defines a fallback function that delegates all calls to the address
 * returned by the abstract _implementation() internal function.
 */
abstract contract Proxy {
  /**
   * @dev Fallback function.
   * Implemented entirely in `_fallback`.
   */
  fallback () payable external {
    _fallback();
  }
  /**
   * @return The Address of the implementation.
   */
  function _implementation() internal virtual view returns (address);
  /**
   * @dev Delegates execution to an implementation contract.
   * This is a low level function that doesn't return to its internal call site.
   * It will return to the external caller whatever the implementation returns.
   * @param implementation Address to delegate.
   */
  function _delegate(address implementation) internal {
    assembly {
      // Copy msg.data. We take full control of memory in this inline assembly
      // block because it will not return to Solidity code. We overwrite the
      // Solidity scratch pad at memory position 0.
      calldatacopy(0, 0, calldatasize())
      // Call the implementation.
      // out and outsize are 0 because we don't know the size yet.
      let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)
      // Copy the returned data.
      returndatacopy(0, 0, returndatasize())
      switch result
      // delegatecall returns 0 on error.
      case 0 { revert(0, returndatasize()) }
      default { return(0, returndatasize()) }
    }
  }
  /**
   * @dev Function that is run as the first thing in the fallback function.
   * Can be redefined in derived contracts to add functionality.
   * Redefinitions must call super._willFallback().
   */
  function _willFallback() internal virtual {
  }
  /**
   * @dev fallback implementation.
   * Extracted to enable manual triggering.
   */
  function _fallback() internal {
    _willFallback();
    _delegate(_implementation());
  }
}// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;
/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;
import "./Context.sol";
import "../interfaces/IERC20.sol";
import "./SafeMath.sol";
import "./Address.sol";
/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;
    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;
    uint256 private _totalSupply;
    string internal _name;
    string internal _symbol;
    uint8 private _decimals;
    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }
    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }
    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }
    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }
    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }
    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }
    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }
    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }
    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }
    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _beforeTokenTransfer(sender, recipient, amount);
        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }
    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");
        _beforeTokenTransfer(address(0), account, amount);
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }
    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");
        _beforeTokenTransfer(account, address(0), amount);
        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }
    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }
    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}pragma solidity ^0.6.0;
/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }
    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }
    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;
        return c;
    }
    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }
    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }
    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return c;
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.10;
import "./BaseAdminUpgradeabilityProxy.sol";
import "./InitializableUpgradeabilityProxy.sol";
/**
 * @title InitializableAdminUpgradeabilityProxy
 * @dev Extends from BaseAdminUpgradeabilityProxy with an initializer for 
 * initializing the implementation, admin, and init data.
 */
contract InitializableAdminUpgradeabilityProxy is BaseAdminUpgradeabilityProxy, InitializableUpgradeabilityProxy {
    /**
   * Contract initializer.
   * @param _logic address of the initial implementation.
   * @param _admin Address of the proxy administrator.
   * @param _data Data to send as msg.data to the implementation to initialize the proxied contract.
   * It should include the signature and the parameters of the function to be called, as described in
   * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
   * This parameter is optional, if no data is given the initialization call to proxied contract will be skipped.
   */
    function initialize(address _logic, address _admin, bytes memory _data) public payable {
        require(_implementation() == address(0));
        InitializableUpgradeabilityProxy.initialize(_logic, _data);
        assert(ADMIN_SLOT == bytes32(uint256(keccak256("eip1967.proxy.admin")) - 1));
        _setAdmin(_admin);
    }
    /**
    * @dev Only fall back when the sender is not the admin.
    */
    function _willFallback() internal override(BaseAdminUpgradeabilityProxy, Proxy) {
        BaseAdminUpgradeabilityProxy._willFallback();
    }
}
// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.10;
import "./BaseUpgradeabilityProxy.sol";
/**
 * @title InitializableUpgradeabilityProxy
 * @dev Extends BaseUpgradeabilityProxy with an initializer for initializing
 * implementation and init data.
 */
contract InitializableUpgradeabilityProxy is BaseUpgradeabilityProxy {
    /**
   * @dev Contract initializer.
   * @param _logic Address of the initial implementation.
   * @param _data Data to send as msg.data to the implementation to initialize the proxied contract.
   * It should include the signature and the parameters of the function to be called, as described in
   * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
   * This parameter is optional, if no data is given the initialization call to proxied contract will be skipped.
   */
    function initialize(address _logic, bytes memory _data) public payable {
        require(_implementation() == address(0));
        assert(IMPLEMENTATION_SLOT == bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1));
        _setImplementation(_logic);
        if (_data.length > 0) {
            (bool success, ) = _logic.delegatecall(_data);
            require(success);
        }
    }
}
// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import {ERC20} from "../open-zeppelin/ERC20.sol";
import {ITransferHook} from "../interfaces/ITransferHook.sol";
import {VersionedInitializable} from "../utils/VersionedInitializable.sol";
/**
* @notice implementation of the AAVE token contract
* @author Aave
*/
contract AaveToken is ERC20, VersionedInitializable {
    /// @dev snapshot of a value on a specific block, used for balances
    struct Snapshot {
        uint128 blockNumber;
        uint128 value;
    }
    string internal constant NAME = "Aave Token";
    string internal constant SYMBOL = "AAVE";
    uint8 internal constant DECIMALS = 18;
    /// @dev the amount being distributed for the LEND -> AAVE migration
    uint256 internal constant MIGRATION_AMOUNT = 13000000 ether;
    /// @dev the amount being distributed for the PSI and PEI
    uint256 internal constant DISTRIBUTION_AMOUNT = 3000000 ether;
    uint256 public constant REVISION = 1;
    /// @dev owner => next valid nonce to submit with permit()
    mapping (address => uint256) public _nonces;
    mapping (address => mapping (uint256 => Snapshot)) public _snapshots;
    mapping (address => uint256) public _countsSnapshots;
    /// @dev reference to the Aave governance contract to call (if initialized) on _beforeTokenTransfer
    /// !!! IMPORTANT The Aave governance is considered a trustable contract, being its responsibility
    /// to control all potential reentrancies by calling back the AaveToken
    ITransferHook public _aaveGovernance;
    bytes32 public DOMAIN_SEPARATOR;
    bytes public constant EIP712_REVISION = bytes("1");
    bytes32 internal constant EIP712_DOMAIN = keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");
    bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    event SnapshotDone(address owner, uint128 oldValue, uint128 newValue);
    constructor() ERC20(NAME, SYMBOL) public {}
    /**
    * @dev initializes the contract upon assignment to the InitializableAdminUpgradeabilityProxy
    * @param migrator the address of the LEND -> AAVE migration contract
    * @param distributor the address of the AAVE distribution contract
    */
    function initialize(
        address migrator,
        address distributor,
        ITransferHook aaveGovernance
    ) external initializer {
        uint256 chainId;
        //solium-disable-next-line
        assembly {
            chainId := chainid()
        }
        DOMAIN_SEPARATOR = keccak256(abi.encode(
            EIP712_DOMAIN,
            keccak256(bytes(NAME)),
            keccak256(EIP712_REVISION),
            chainId,
            address(this)
        ));
        _name = NAME;
        _symbol = SYMBOL;
        _setupDecimals(DECIMALS);
        _aaveGovernance = aaveGovernance;
        _mint(migrator, MIGRATION_AMOUNT);
        _mint(distributor, DISTRIBUTION_AMOUNT);
    }
    /**
    * @dev implements the permit function as for https://github.com/ethereum/EIPs/blob/8a34d644aacf0f9f8f00815307fd7dd5da07655f/EIPS/eip-2612.md
    * @param owner the owner of the funds
    * @param spender the spender
    * @param value the amount
    * @param deadline the deadline timestamp, type(uint256).max for no deadline
    * @param v signature param
    * @param s signature param
    * @param r signature param
    */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external {
        require(owner != address(0), "INVALID_OWNER");
        //solium-disable-next-line
        require(block.timestamp <= deadline, "INVALID_EXPIRATION");
        uint256 currentValidNonce = _nonces[owner];
        bytes32 digest = keccak256(
                abi.encodePacked(
                    "\\x19\\x01",
                    DOMAIN_SEPARATOR,
                    keccak256(
                        abi.encode(PERMIT_TYPEHASH, owner, spender, value, currentValidNonce, deadline))
                    )
        );
        require(owner == ecrecover(digest, v, r, s), "INVALID_SIGNATURE");
        _nonces[owner] = currentValidNonce.add(1);
        _approve(owner, spender, value);
    }
    /**
    * @dev returns the revision of the implementation contract
    */
    function getRevision() internal pure override returns (uint256) {
        return REVISION;
    }
    /**
    * @dev Writes a snapshot for an owner of tokens
    * @param owner The owner of the tokens
    * @param oldValue The value before the operation that is gonna be executed after the snapshot
    * @param newValue The value after the operation
    */
    function _writeSnapshot(address owner, uint128 oldValue, uint128 newValue) internal {
        uint128 currentBlock = uint128(block.number);
        uint256 ownerCountOfSnapshots = _countsSnapshots[owner];
        mapping (uint256 => Snapshot) storage snapshotsOwner = _snapshots[owner];
        // Doing multiple operations in the same block
        if (ownerCountOfSnapshots != 0 && snapshotsOwner[ownerCountOfSnapshots.sub(1)].blockNumber == currentBlock) {
            snapshotsOwner[ownerCountOfSnapshots.sub(1)].value = newValue;
        } else {
            snapshotsOwner[ownerCountOfSnapshots] = Snapshot(currentBlock, newValue);
            _countsSnapshots[owner] = ownerCountOfSnapshots.add(1);
        }
        emit SnapshotDone(owner, oldValue, newValue);
    }
    /**
    * @dev Writes a snapshot before any operation involving transfer of value: _transfer, _mint and _burn
    * - On _transfer, it writes snapshots for both "from" and "to"
    * - On _mint, only for _to
    * - On _burn, only for _from
    * @param from the from address
    * @param to the to address
    * @param amount the amount to transfer
    */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal override {
        if (from == to) {
            return;
        }
        if (from != address(0)) {
            uint256 fromBalance = balanceOf(from);
            _writeSnapshot(from, uint128(fromBalance), uint128(fromBalance.sub(amount)));
        }
        if (to != address(0)) {
            uint256 toBalance = balanceOf(to);
            _writeSnapshot(to, uint128(toBalance), uint128(toBalance.add(amount)));
        }
        // caching the aave governance address to avoid multiple state loads
        ITransferHook aaveGovernance = _aaveGovernance;
        if (aaveGovernance != ITransferHook(0)) {
            aaveGovernance.onTransfer(from, to, amount);
        }
    }
}// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
/**
 * @title VersionedInitializable
 *
 * @dev Helper contract to support initializer functions. To use it, replace
 * the constructor with a function that has the `initializer` modifier.
 * WARNING: Unlike constructors, initializer functions must be manually
 * invoked. This applies both to deploying an Initializable contract, as well
 * as extending an Initializable contract via inheritance.
 * WARNING: When used with inheritance, manual care must be taken to not invoke
 * a parent initializer twice, or ensure that all initializers are idempotent,
 * because this is not dealt with automatically as with constructors.
 *
 * @author Aave, inspired by the OpenZeppelin Initializable contract
 */
abstract contract VersionedInitializable {
    /**
   * @dev Indicates that the contract has been initialized.
   */
    uint256 internal lastInitializedRevision = 0;
   /**
   * @dev Modifier to use in the initializer function of a contract.
   */
    modifier initializer() {
        uint256 revision = getRevision();
        require(revision > lastInitializedRevision, "Contract instance has already been initialized");
        lastInitializedRevision = revision;
        _;
    }
    /// @dev returns the revision number of the contract.
    /// Needs to be defined in the inherited class as a constant.
    function getRevision() internal pure virtual returns(uint256);
    // Reserved storage space to allow for layout changes in the future.
    uint256[50] private ______gap;
}
// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import {IERC20} from "../interfaces/IERC20.sol";
import {SafeMath} from "../open-zeppelin/SafeMath.sol";
import {VersionedInitializable} from "../utils/VersionedInitializable.sol";
/**
* @title LendToAaveMigrator
* @notice This contract implements the migration from LEND to AAVE token
* @author Aave 
*/
contract LendToAaveMigrator is VersionedInitializable {
    using SafeMath for uint256;
    IERC20 public immutable AAVE;
    IERC20 public immutable LEND;
    uint256 public immutable LEND_AAVE_RATIO;
    uint256 public constant REVISION = 1;
    
    uint256 public _totalLendMigrated;
    /**
    * @dev emitted on migration
    * @param sender the caller of the migration
    * @param amount the amount being migrated
    */
    event LendMigrated(address indexed sender, uint256 indexed amount);
    /**
    * @param aave the address of the AAVE token
    * @param lend the address of the LEND token
    * @param lendAaveRatio the exchange rate between LEND and AAVE 
     */
    constructor(IERC20 aave, IERC20 lend, uint256 lendAaveRatio) public {
        AAVE = aave;
        LEND = lend;
        LEND_AAVE_RATIO = lendAaveRatio;
    }
    /**
    * @dev initializes the implementation
    */
    function initialize() public initializer {
    }
    /**
    * @dev returns true if the migration started
    */
    function migrationStarted() external view returns(bool) {
        return lastInitializedRevision != 0;
    }
    /**
    * @dev executes the migration from LEND to AAVE. Users need to give allowance to this contract to transfer LEND before executing
    * this transaction.
    * @param amount the amount of LEND to be migrated
    */
    function migrateFromLEND(uint256 amount) external {
        require(lastInitializedRevision != 0, "MIGRATION_NOT_STARTED");
        _totalLendMigrated = _totalLendMigrated.add(amount);
        LEND.transferFrom(msg.sender, address(this), amount);
        AAVE.transfer(msg.sender, amount.div(LEND_AAVE_RATIO));
        emit LendMigrated(msg.sender, amount);
    }
    /**
    * @dev returns the implementation revision
    * @return the implementation revision
    */
    function getRevision() internal pure override returns (uint256) {
        return REVISION;
    }
}// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import "../interfaces/IERC20.sol";
contract DoubleTransferHelper {
    IERC20 public immutable AAVE;
    constructor(IERC20 aave) public {
        AAVE = aave;
    }
    function doubleSend(address to, uint256 amount1, uint256 amount2) external {
        AAVE.transfer(to, amount1);
        AAVE.transfer(to, amount2);
    }
}// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import "../open-zeppelin/ERC20.sol";
/**
 * @title ERC20Mintable
 * @dev ERC20 minting logic
 */
contract MintableErc20 is ERC20 {
    constructor(string memory name, string memory symbol, uint8 decimals) ERC20(name, symbol) public {
        _setupDecimals(decimals);
    }
    /**
     * @dev Function to mint tokens
     * @param value The amount of tokens to mint.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(uint256 value) public returns (bool) {
        _mint(msg.sender, value);
        return true;
    }
}
// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.10;
import {ITransferHook} from "../interfaces/ITransferHook.sol";
contract MockTransferHook is ITransferHook {
    event MockHookEvent();
    function onTransfer(address from, address to, uint256 amount) external override {
        emit MockHookEvent();
    }
}

// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.7.5;
pragma experimental ABIEncoderV2;


interface IGovernancePowerDelegationToken {
  
  enum DelegationType {VOTING_POWER, PROPOSITION_POWER}

  /**
   * @dev emitted when a user delegates to another
   * @param delegator the delegator
   * @param delegatee the delegatee
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  event DelegateChanged(
    address indexed delegator,
    address indexed delegatee,
    DelegationType delegationType
  );

  /**
   * @dev emitted when an action changes the delegated power of a user
   * @param user the user which delegated power has changed
   * @param amount the amount of delegated power for the user
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  event DelegatedPowerChanged(address indexed user, uint256 amount, DelegationType delegationType);

  /**
   * @dev delegates the specific power to a delegatee
   * @param delegatee the user which delegated power has changed
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  function delegateByType(address delegatee, DelegationType delegationType) external virtual;
  /**
   * @dev delegates all the powers to a specific user
   * @param delegatee the user to which the power will be delegated
   **/
  function delegate(address delegatee) external virtual;
  /**
   * @dev returns the delegatee of an user
   * @param delegator the address of the delegator
   **/
  function getDelegateeByType(address delegator, DelegationType delegationType)
    external
    virtual
    view
    returns (address);

  /**
   * @dev returns the current delegated power of a user. The current power is the
   * power delegated at the time of the last snapshot
   * @param user the user
   **/
  function getPowerCurrent(address user, DelegationType delegationType)
    external
    virtual
    view
    returns (uint256);

  /**
   * @dev returns the delegated power of a user at a certain block
   * @param user the user
   **/
  function getPowerAtBlock(
    address user,
    uint256 blockNumber,
    DelegationType delegationType
  ) external virtual view returns (uint256);
 
  /**
  * @dev returns the total supply at a certain block number
  **/
  function totalSupplyAt(uint256 blockNumber) external virtual view returns (uint256);
}

/**
 * @dev From https://github.com/OpenZeppelin/openzeppelin-contracts
 * Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
  function _msgSender() internal view virtual returns (address payable) {
    return msg.sender;
  }

  function _msgData() internal view virtual returns (bytes memory) {
    this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
    return msg.data;
  }
}


/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 * From https://github.com/OpenZeppelin/openzeppelin-contracts
 */
interface IERC20 {
  /**
   * @dev Returns the amount of tokens in existence.
   */
  function totalSupply() external view returns (uint256);

  /**
   * @dev Returns the amount of tokens owned by `account`.
   */
  function balanceOf(address account) external view returns (uint256);

  /**
   * @dev Moves `amount` tokens from the caller's account to `recipient`.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * Emits a {Transfer} event.
   */
  function transfer(address recipient, uint256 amount) external returns (bool);

  /**
   * @dev Returns the remaining number of tokens that `spender` will be
   * allowed to spend on behalf of `owner` through {transferFrom}. This is
   * zero by default.
   *
   * This value changes when {approve} or {transferFrom} are called.
   */
  function allowance(address owner, address spender) external view returns (uint256);

  /**
   * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * IMPORTANT: Beware that changing an allowance with this method brings the risk
   * that someone may use both the old and the new allowance by unfortunate
   * transaction ordering. One possible solution to mitigate this race
   * condition is to first reduce the spender's allowance to 0 and set the
   * desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   *
   * Emits an {Approval} event.
   */
  function approve(address spender, uint256 amount) external returns (bool);

  /**
   * @dev Moves `amount` tokens from `sender` to `recipient` using the
   * allowance mechanism. `amount` is then deducted from the caller's
   * allowance.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * Emits a {Transfer} event.
   */
  function transferFrom(
    address sender,
    address recipient,
    uint256 amount
  ) external returns (bool);

  /**
   * @dev Emitted when `value` tokens are moved from one account (`from`) to
   * another (`to`).
   *
   * Note that `value` may be zero.
   */
  event Transfer(address indexed from, address indexed to, uint256 value);

  /**
   * @dev Emitted when the allowance of a `spender` for an `owner` is set by
   * a call to {approve}. `value` is the new allowance.
   */
  event Approval(address indexed owner, address indexed spender, uint256 value);
}



/**
 * @dev From https://github.com/OpenZeppelin/openzeppelin-contracts
 * Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
  /**
   * @dev Returns the addition of two unsigned integers, reverting on
   * overflow.
   *
   * Counterpart to Solidity's `+` operator.
   *
   * Requirements:
   * - Addition cannot overflow.
   */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, 'SafeMath: addition overflow');

    return c;
  }

  /**
   * @dev Returns the subtraction of two unsigned integers, reverting on
   * overflow (when the result is negative).
   *
   * Counterpart to Solidity's `-` operator.
   *
   * Requirements:
   * - Subtraction cannot overflow.
   */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, 'SafeMath: subtraction overflow');
  }

  /**
   * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
   * overflow (when the result is negative).
   *
   * Counterpart to Solidity's `-` operator.
   *
   * Requirements:
   * - Subtraction cannot overflow.
   */
  function sub(
    uint256 a,
    uint256 b,
    string memory errorMessage
  ) internal pure returns (uint256) {
    require(b <= a, errorMessage);
    uint256 c = a - b;

    return c;
  }

  /**
   * @dev Returns the multiplication of two unsigned integers, reverting on
   * overflow.
   *
   * Counterpart to Solidity's `*` operator.
   *
   * Requirements:
   * - Multiplication cannot overflow.
   */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b, 'SafeMath: multiplication overflow');

    return c;
  }

  /**
   * @dev Returns the integer division of two unsigned integers. Reverts on
   * division by zero. The result is rounded towards zero.
   *
   * Counterpart to Solidity's `/` operator. Note: this function uses a
   * `revert` opcode (which leaves remaining gas untouched) while Solidity
   * uses an invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, 'SafeMath: division by zero');
  }

  /**
   * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
   * division by zero. The result is rounded towards zero.
   *
   * Counterpart to Solidity's `/` operator. Note: this function uses a
   * `revert` opcode (which leaves remaining gas untouched) while Solidity
   * uses an invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function div(
    uint256 a,
    uint256 b,
    string memory errorMessage
  ) internal pure returns (uint256) {
    // Solidity only automatically asserts when dividing by 0
    require(b > 0, errorMessage);
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
   * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
   * Reverts when dividing by zero.
   *
   * Counterpart to Solidity's `%` operator. This function uses a `revert`
   * opcode (which leaves remaining gas untouched) while Solidity uses an
   * invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, 'SafeMath: modulo by zero');
  }

  /**
   * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
   * Reverts with custom message when dividing by zero.
   *
   * Counterpart to Solidity's `%` operator. This function uses a `revert`
   * opcode (which leaves remaining gas untouched) while Solidity uses an
   * invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function mod(
    uint256 a,
    uint256 b,
    string memory errorMessage
  ) internal pure returns (uint256) {
    require(b != 0, errorMessage);
    return a % b;
  }
}



/**
 * @dev Collection of functions related to the address type
 * From https://github.com/OpenZeppelin/openzeppelin-contracts
 */
library Address {
  /**
   * @dev Returns true if `account` is a contract.
   *
   * [IMPORTANT]
   * ====
   * It is unsafe to assume that an address for which this function returns
   * false is an externally-owned account (EOA) and not a contract.
   *
   * Among others, `isContract` will return false for the following
   * types of addresses:
   *
   *  - an externally-owned account
   *  - a contract in construction
   *  - an address where a contract will be created
   *  - an address where a contract lived, but was destroyed
   * ====
   */
  function isContract(address account) internal view returns (bool) {
    // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
    // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
    // for accounts without code, i.e. `keccak256('')`
    bytes32 codehash;
    bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
    // solhint-disable-next-line no-inline-assembly
    assembly {
      codehash := extcodehash(account)
    }
    return (codehash != accountHash && codehash != 0x0);
  }

  /**
   * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
   * `recipient`, forwarding all available gas and reverting on errors.
   *
   * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
   * of certain opcodes, possibly making contracts go over the 2300 gas limit
   * imposed by `transfer`, making them unable to receive funds via
   * `transfer`. {sendValue} removes this limitation.
   *
   * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
   *
   * IMPORTANT: because control is transferred to `recipient`, care must be
   * taken to not create reentrancy vulnerabilities. Consider using
   * {ReentrancyGuard} or the
   * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
   */
  function sendValue(address payable recipient, uint256 amount) internal {
    require(address(this).balance >= amount, 'Address: insufficient balance');

    // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
    (bool success, ) = recipient.call{value: amount}('');
    require(success, 'Address: unable to send value, recipient may have reverted');
  }
}

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string internal _name;
    string internal _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

interface ITransferHook {
  function onTransfer(
    address from,
    address to,
    uint256 amount
  ) external;
}


/**
 * @title SafeERC20
 * @dev From https://github.com/OpenZeppelin/openzeppelin-contracts
 * Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
  using SafeMath for uint256;
  using Address for address;

  function safeTransfer(
    IERC20 token,
    address to,
    uint256 value
  ) internal {
    callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
  }

  function safeTransferFrom(
    IERC20 token,
    address from,
    address to,
    uint256 value
  ) internal {
    callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
  }

  function safeApprove(
    IERC20 token,
    address spender,
    uint256 value
  ) internal {
    require(
      (value == 0) || (token.allowance(address(this), spender) == 0),
      'SafeERC20: approve from non-zero to non-zero allowance'
    );
    callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
  }

  function callOptionalReturn(IERC20 token, bytes memory data) private {
    require(address(token).isContract(), 'SafeERC20: call to non-contract');

    // solhint-disable-next-line avoid-low-level-calls
    (bool success, bytes memory returndata) = address(token).call(data);
    require(success, 'SafeERC20: low-level call failed');

    if (returndata.length > 0) {
      // Return data is optional
      // solhint-disable-next-line max-line-length
      require(abi.decode(returndata, (bool)), 'SafeERC20: ERC20 operation did not succeed');
    }
  }
}

/**
 * @title VersionedInitializable
 *
 * @dev Helper contract to support initializer functions. To use it, replace
 * the constructor with a function that has the `initializer` modifier.
 * WARNING: Unlike constructors, initializer functions must be manually
 * invoked. This applies both to deploying an Initializable contract, as well
 * as extending an Initializable contract via inheritance.
 * WARNING: When used with inheritance, manual care must be taken to not invoke
 * a parent initializer twice, or ensure that all initializers are idempotent,
 * because this is not dealt with automatically as with constructors.
 *
 * @author Aave, inspired by the OpenZeppelin Initializable contract
 */
abstract contract VersionedInitializable {
  /**
   * @dev Indicates that the contract has been initialized.
   */
  uint256 internal lastInitializedRevision = 0;

  /**
   * @dev Modifier to use in the initializer function of a contract.
   */
  modifier initializer() {
    uint256 revision = getRevision();
    require(revision > lastInitializedRevision, 'Contract instance has already been initialized');

    lastInitializedRevision = revision;

    _;
  }

  /// @dev returns the revision number of the contract.
  /// Needs to be defined in the inherited class as a constant.
  function getRevision() internal pure virtual returns (uint256);

  // Reserved storage space to allow for layout changes in the future.
  uint256[50] private ______gap;
}




/**
 * @notice implementation of the AAVE token contract
 * @author Aave
 */
abstract contract GovernancePowerDelegationERC20 is ERC20, IGovernancePowerDelegationToken {
  using SafeMath for uint256;
  /// @notice The EIP-712 typehash for the delegation struct used by the contract
  bytes32 public constant DELEGATE_BY_TYPE_TYPEHASH = keccak256(
    'DelegateByType(address delegatee,uint256 type,uint256 nonce,uint256 expiry)'
  );

  bytes32 public constant DELEGATE_TYPEHASH = keccak256(
    'Delegate(address delegatee,uint256 nonce,uint256 expiry)'
  );

  /// @dev snapshot of a value on a specific block, used for votes
  struct Snapshot {
    uint128 blockNumber;
    uint128 value;
  }

  /**
   * @dev delegates one specific power to a delegatee
   * @param delegatee the user which delegated power has changed
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  function delegateByType(address delegatee, DelegationType delegationType) external override {
    _delegateByType(msg.sender, delegatee, delegationType);
  }

  /**
   * @dev delegates all the powers to a specific user
   * @param delegatee the user to which the power will be delegated
   **/
  function delegate(address delegatee) external override {
    _delegateByType(msg.sender, delegatee, DelegationType.VOTING_POWER);
    _delegateByType(msg.sender, delegatee, DelegationType.PROPOSITION_POWER);
  }

  /**
   * @dev returns the delegatee of an user
   * @param delegator the address of the delegator
   **/
  function getDelegateeByType(address delegator, DelegationType delegationType)
    external
    override
    view
    returns (address)
  {
    (, , mapping(address => address) storage delegates) = _getDelegationDataByType(delegationType);

    return _getDelegatee(delegator, delegates);
  }

  /**
   * @dev returns the current delegated power of a user. The current power is the
   * power delegated at the time of the last snapshot
   * @param user the user
   **/
  function getPowerCurrent(address user, DelegationType delegationType)
    external
    override
    view
    returns (uint256)
  {
    (
      mapping(address => mapping(uint256 => Snapshot)) storage snapshots,
      mapping(address => uint256) storage snapshotsCounts,

    ) = _getDelegationDataByType(delegationType);

    return _searchByBlockNumber(snapshots, snapshotsCounts, user, block.number);
  }

  /**
   * @dev returns the delegated power of a user at a certain block
   * @param user the user
   **/
  function getPowerAtBlock(
    address user,
    uint256 blockNumber,
    DelegationType delegationType
  ) external override view returns (uint256) {
    (
      mapping(address => mapping(uint256 => Snapshot)) storage snapshots,
      mapping(address => uint256) storage snapshotsCounts,

    ) = _getDelegationDataByType(delegationType);

    return _searchByBlockNumber(snapshots, snapshotsCounts, user, blockNumber);
  }

  /**
   * @dev returns the total supply at a certain block number
   * used by the voting strategy contracts to calculate the total votes needed for threshold/quorum
   * In this initial implementation with no AAVE minting, simply returns the current supply
   * A snapshots mapping will need to be added in case a mint function is added to the AAVE token in the future
   **/
  function totalSupplyAt(uint256 blockNumber) external override view returns (uint256) {
    return super.totalSupply();
  }

  /**
   * @dev delegates the specific power to a delegatee
   * @param delegatee the user which delegated power has changed
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  function _delegateByType(
    address delegator,
    address delegatee,
    DelegationType delegationType
  ) internal {
    require(delegatee != address(0), 'INVALID_DELEGATEE');

    (, , mapping(address => address) storage delegates) = _getDelegationDataByType(delegationType);

    uint256 delegatorBalance = balanceOf(delegator);

    address previousDelegatee = _getDelegatee(delegator, delegates);

    delegates[delegator] = delegatee;

    _moveDelegatesByType(previousDelegatee, delegatee, delegatorBalance, delegationType);
    emit DelegateChanged(delegator, delegatee, delegationType);
  }

  /**
   * @dev moves delegated power from one user to another
   * @param from the user from which delegated power is moved
   * @param to the user that will receive the delegated power
   * @param amount the amount of delegated power to be moved
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   **/
  function _moveDelegatesByType(
    address from,
    address to,
    uint256 amount,
    DelegationType delegationType
  ) internal {
    if (from == to) {
      return;
    }

    (
      mapping(address => mapping(uint256 => Snapshot)) storage snapshots,
      mapping(address => uint256) storage snapshotsCounts,

    ) = _getDelegationDataByType(delegationType);

    if (from != address(0)) {
      uint256 previous = 0;
      uint256 fromSnapshotsCount = snapshotsCounts[from];

      if (fromSnapshotsCount != 0) {
        previous = snapshots[from][fromSnapshotsCount - 1].value;
      } else {
        previous = balanceOf(from);
      }

      _writeSnapshot(
        snapshots,
        snapshotsCounts,
        from,
        uint128(previous),
        uint128(previous.sub(amount))
      );

      emit DelegatedPowerChanged(from, previous.sub(amount), delegationType);
    }
    if (to != address(0)) {
      uint256 previous = 0;
      uint256 toSnapshotsCount = snapshotsCounts[to];
      if (toSnapshotsCount != 0) {
        previous = snapshots[to][toSnapshotsCount - 1].value;
      } else {
        previous = balanceOf(to);
      }

      _writeSnapshot(
        snapshots,
        snapshotsCounts,
        to,
        uint128(previous),
        uint128(previous.add(amount))
      );

      emit DelegatedPowerChanged(to, previous.add(amount), delegationType);
    }
  }

  /**
   * @dev searches a snapshot by block number. Uses binary search.
   * @param snapshots the snapshots mapping
   * @param snapshotsCounts the number of snapshots
   * @param user the user for which the snapshot is being searched
   * @param blockNumber the block number being searched
   **/
  function _searchByBlockNumber(
    mapping(address => mapping(uint256 => Snapshot)) storage snapshots,
    mapping(address => uint256) storage snapshotsCounts,
    address user,
    uint256 blockNumber
  ) internal view returns (uint256) {
    require(blockNumber <= block.number, 'INVALID_BLOCK_NUMBER');

    uint256 snapshotsCount = snapshotsCounts[user];

    if (snapshotsCount == 0) {
      return balanceOf(user);
    }

    // First check most recent balance
    if (snapshots[user][snapshotsCount - 1].blockNumber <= blockNumber) {
      return snapshots[user][snapshotsCount - 1].value;
    }

    // Next check implicit zero balance
    if (snapshots[user][0].blockNumber > blockNumber) {
      return 0;
    }

    uint256 lower = 0;
    uint256 upper = snapshotsCount - 1;
    while (upper > lower) {
      uint256 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
      Snapshot memory snapshot = snapshots[user][center];
      if (snapshot.blockNumber == blockNumber) {
        return snapshot.value;
      } else if (snapshot.blockNumber < blockNumber) {
        lower = center;
      } else {
        upper = center - 1;
      }
    }
    return snapshots[user][lower].value;
  }

  /**
   * @dev returns the delegation data (snapshot, snapshotsCount, list of delegates) by delegation type
   * NOTE: Ideal implementation would have mapped this in a struct by delegation type. Unfortunately,
   * the AAVE token and StakeToken already include a mapping for the snapshots, so we require contracts
   * who inherit from this to provide access to the delegation data by overriding this method.
   * @param delegationType the type of delegation
   **/
  function _getDelegationDataByType(DelegationType delegationType)
    internal
    virtual
    view
    returns (
      mapping(address => mapping(uint256 => Snapshot)) storage, //snapshots
      mapping(address => uint256) storage, //snapshots count
      mapping(address => address) storage //delegatees list
    );

  /**
   * @dev Writes a snapshot for an owner of tokens
   * @param owner The owner of the tokens
   * @param oldValue The value before the operation that is gonna be executed after the snapshot
   * @param newValue The value after the operation
   */
  function _writeSnapshot(
    mapping(address => mapping(uint256 => Snapshot)) storage snapshots,
    mapping(address => uint256) storage snapshotsCounts,
    address owner,
    uint128 oldValue,
    uint128 newValue
  ) internal {
    uint128 currentBlock = uint128(block.number);

    uint256 ownerSnapshotsCount = snapshotsCounts[owner];
    mapping(uint256 => Snapshot) storage snapshotsOwner = snapshots[owner];

    // Doing multiple operations in the same block
    if (
      ownerSnapshotsCount != 0 &&
      snapshotsOwner[ownerSnapshotsCount - 1].blockNumber == currentBlock
    ) {
      snapshotsOwner[ownerSnapshotsCount - 1].value = newValue;
    } else {
      snapshotsOwner[ownerSnapshotsCount] = Snapshot(currentBlock, newValue);
      snapshotsCounts[owner] = ownerSnapshotsCount + 1;
    }
  }

  /**
   * @dev returns the user delegatee. If a user never performed any delegation,
   * his delegated address will be 0x0. In that case we simply return the user itself
   * @param delegator the address of the user for which return the delegatee
   * @param delegates the array of delegates for a particular type of delegation
   **/
  function _getDelegatee(address delegator, mapping(address => address) storage delegates)
    internal
    view
    returns (address)
  {
    address previousDelegatee = delegates[delegator];

    if (previousDelegatee == address(0)) {
      return delegator;
    }

    return previousDelegatee;
  }
}

/**
 * @notice implementation of the AAVE token contract
 * @author Aave
 */
contract AaveTokenV2 is GovernancePowerDelegationERC20, VersionedInitializable {
  using SafeMath for uint256;

  string internal constant NAME = 'Aave Token';
  string internal constant SYMBOL = 'AAVE';
  uint8 internal constant DECIMALS = 18;

  uint256 public constant REVISION = 2;

  /// @dev owner => next valid nonce to submit with permit()
  mapping(address => uint256) public _nonces;

  mapping(address => mapping(uint256 => Snapshot)) public _votingSnapshots;

  mapping(address => uint256) public _votingSnapshotsCounts;

  /// @dev reference to the Aave governance contract to call (if initialized) on _beforeTokenTransfer
  /// !!! IMPORTANT The Aave governance is considered a trustable contract, being its responsibility
  /// to control all potential reentrancies by calling back the AaveToken
  ITransferHook public _aaveGovernance;

  bytes32 public DOMAIN_SEPARATOR;
  bytes public constant EIP712_REVISION = bytes('1');
  bytes32 internal constant EIP712_DOMAIN = keccak256(
    'EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'
  );
  bytes32 public constant PERMIT_TYPEHASH = keccak256(
    'Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)'
  );

  mapping(address => address) internal _votingDelegates;

  mapping(address => mapping(uint256 => Snapshot)) internal _propositionPowerSnapshots;
  mapping(address => uint256) internal _propositionPowerSnapshotsCounts;

  mapping(address => address) internal _propositionPowerDelegates;

  constructor() public ERC20(NAME, SYMBOL) {}

  /**
   * @dev initializes the contract upon assignment to the InitializableAdminUpgradeabilityProxy
   */
  function initialize() external initializer {}

  /**
   * @dev implements the permit function as for https://github.com/ethereum/EIPs/blob/8a34d644aacf0f9f8f00815307fd7dd5da07655f/EIPS/eip-2612.md
   * @param owner the owner of the funds
   * @param spender the spender
   * @param value the amount
   * @param deadline the deadline timestamp, type(uint256).max for no deadline
   * @param v signature param
   * @param s signature param
   * @param r signature param
   */

  function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) external {
    require(owner != address(0), 'INVALID_OWNER');
    //solium-disable-next-line
    require(block.timestamp <= deadline, 'INVALID_EXPIRATION');
    uint256 currentValidNonce = _nonces[owner];
    bytes32 digest = keccak256(
      abi.encodePacked(
        '\x19\x01',
        DOMAIN_SEPARATOR,
        keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, currentValidNonce, deadline))
      )
    );

    require(owner == ecrecover(digest, v, r, s), 'INVALID_SIGNATURE');
    _nonces[owner] = currentValidNonce.add(1);
    _approve(owner, spender, value);
  }

  /**
   * @dev returns the revision of the implementation contract
   */
  function getRevision() internal override pure returns (uint256) {
    return REVISION;
  }

  /**
   * @dev Writes a snapshot before any operation involving transfer of value: _transfer, _mint and _burn
   * - On _transfer, it writes snapshots for both "from" and "to"
   * - On _mint, only for _to
   * - On _burn, only for _from
   * @param from the from address
   * @param to the to address
   * @param amount the amount to transfer
   */
  function _beforeTokenTransfer(
    address from,
    address to,
    uint256 amount
  ) internal override {
    address votingFromDelegatee = _getDelegatee(from, _votingDelegates);
    address votingToDelegatee = _getDelegatee(to, _votingDelegates);

    _moveDelegatesByType(
      votingFromDelegatee,
      votingToDelegatee,
      amount,
      DelegationType.VOTING_POWER
    );

    address propPowerFromDelegatee = _getDelegatee(from, _propositionPowerDelegates);
    address propPowerToDelegatee = _getDelegatee(to, _propositionPowerDelegates);

    _moveDelegatesByType(
      propPowerFromDelegatee,
      propPowerToDelegatee,
      amount,
      DelegationType.PROPOSITION_POWER
    );

    // caching the aave governance address to avoid multiple state loads
    ITransferHook aaveGovernance = _aaveGovernance;
    if (aaveGovernance != ITransferHook(0)) {
      aaveGovernance.onTransfer(from, to, amount);
    }
  }

  function _getDelegationDataByType(DelegationType delegationType)
    internal
    override
    view
    returns (
      mapping(address => mapping(uint256 => Snapshot)) storage, //snapshots
      mapping(address => uint256) storage, //snapshots count
      mapping(address => address) storage //delegatees list
    )
  {
    if (delegationType == DelegationType.VOTING_POWER) {
      return (_votingSnapshots, _votingSnapshotsCounts, _votingDelegates);
    } else {
      return (
        _propositionPowerSnapshots,
        _propositionPowerSnapshotsCounts,
        _propositionPowerDelegates
      );
    }
  }

  /**
   * @dev Delegates power from signatory to `delegatee`
   * @param delegatee The address to delegate votes to
   * @param delegationType the type of delegation (VOTING_POWER, PROPOSITION_POWER)
   * @param nonce The contract state required to match the signature
   * @param expiry The time at which to expire the signature
   * @param v The recovery byte of the signature
   * @param r Half of the ECDSA signature pair
   * @param s Half of the ECDSA signature pair
   */
  function delegateByTypeBySig(
    address delegatee,
    DelegationType delegationType,
    uint256 nonce,
    uint256 expiry,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) public {
    bytes32 structHash = keccak256(
      abi.encode(DELEGATE_BY_TYPE_TYPEHASH, delegatee, uint256(delegationType), nonce, expiry)
    );
    bytes32 digest = keccak256(abi.encodePacked('\x19\x01', DOMAIN_SEPARATOR, structHash));
    address signatory = ecrecover(digest, v, r, s);
    require(signatory != address(0), 'INVALID_SIGNATURE');
    require(nonce == _nonces[signatory]++, 'INVALID_NONCE');
    require(block.timestamp <= expiry, 'INVALID_EXPIRATION');
    _delegateByType(signatory, delegatee, delegationType);
  }

  /**
   * @dev Delegates power from signatory to `delegatee`
   * @param delegatee The address to delegate votes to
   * @param nonce The contract state required to match the signature
   * @param expiry The time at which to expire the signature
   * @param v The recovery byte of the signature
   * @param r Half of the ECDSA signature pair
   * @param s Half of the ECDSA signature pair
   */
  function delegateBySig(
    address delegatee,
    uint256 nonce,
    uint256 expiry,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) public {
    bytes32 structHash = keccak256(abi.encode(DELEGATE_TYPEHASH, delegatee, nonce, expiry));
    bytes32 digest = keccak256(abi.encodePacked('\x19\x01', DOMAIN_SEPARATOR, structHash));
    address signatory = ecrecover(digest, v, r, s);
    require(signatory != address(0), 'INVALID_SIGNATURE');
    require(nonce == _nonces[signatory]++, 'INVALID_NONCE');
    require(block.timestamp <= expiry, 'INVALID_EXPIRATION');
    _delegateByType(signatory, delegatee, DelegationType.VOTING_POWER);
    _delegateByType(signatory, delegatee, DelegationType.PROPOSITION_POWER);
  }
}