// Sources flattened with hardhat v2.3.0 https://hardhat.org

// File @openzeppelin/contracts/token/ERC20/IERC20.sol@v3.2.0

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

/**
 * @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);
}


// File contracts/MultiTransfer.sol

contract MultiTransfer {
    uint256 private constant S_NOT_ENTERED = 1;
    uint256 private constant S_ENTERED = 2;
    uint256 private _status = S_NOT_ENTERED;

    function multiTransferERC20(address token, address[] calldata recipients, uint256[] calldata amounts) external {
        uint256 count = recipients.length;
        require(
               _status == S_NOT_ENTERED
            && count > 0
        , "Not authorized.");
        _status = S_ENTERED;

        bool failed;
        address recipient;
        uint256 amount;
        for (uint256 i; i < count; i ++) {
            recipient = recipients[i];
            amount = amounts[i];

            // Ignore bad parameters;
            if (recipient == address(0) || recipient == msg.sender || recipient == address(this) || amount == 0) {
                continue;
            }

            // Attempt the transfer.
            IERC20(token).transferFrom(msg.sender, recipient, amount);
        }

        require(!failed, "Transfer failed!");
        _status = S_NOT_ENTERED;
    }
}