Contract Source Code:

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol


// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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 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 `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, 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 `from` to `to` 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 from,
        address to,
        uint256 amount
    ) external returns (bool);
}

// File: contracts/airdrop.sol


pragma solidity ^0.8.0;
/** Heavily borrowed from Wentokens
https://mirror.xyz/magnatokens.eth/mKAQOM3ntmvcSM5LjX59zFZj5-gYiyqCnEvUu6FDqvw
This is intended to be a stupid simple, opinionated airdrop contract
It should be relatively efficient, but not so advanced that it uses yul/assembly.
Because that stuff is scary.
*/


contract JustAnAirdrop {
    /** Airdrop function
    Usage:
    Include token address and matching arrays of recipients and amounts
    Include total amount of tokens available for airdrop.
    Note: If there are excess tokens, they will be returned to the user
    Note: Relies on the user approving the contract first! */

    function Airdrop (
    IERC20 _token,
    address[] calldata _recipients,
    uint256[] calldata _amounts,
    uint256 _total
    ) external {
        uint256 totalRecipients = _recipients.length; // Number of recipients passed
        require(totalRecipients == _amounts.length, "Number of recipients does not match number of amounts. Something is wrong!");
        require(_token.transferFrom(msg.sender, address(this), _total), "Unable to transfer tokens to contract. Check your balance/approval."); 
        // The dreaded for loop. If this fails due to gas break your drops into smaller batches
        for (uint256 i = 0; i < totalRecipients; i++) {
            _token.transfer(_recipients[i], _amounts[i]);
        }
        // If there are leftover tokens, return them
        // This function should never leave tokens behind, but if someone "donates" tokens it's first come first serve...
        uint256 contractTokenBalance = _token.balanceOf(address(this));
        if (contractTokenBalance > 0) {
            _token.transfer(msg.sender, contractTokenBalance);
        }
    }
}