// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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);
}


contract ExseTokenSale {
    
    uint public ethPrice = 0.0004 ether;
    address payable public owner;
    IERC20 public token;

    struct Sale {
        uint startTime;
        uint finishTime;
    }

    Sale[] public sales;

    modifier onlyOwner() { 
        require(msg.sender == owner, "onlyOwner");
        _; 
    }
    
    constructor(address tokenAddress) public {
        owner = msg.sender;
        token = IERC20(tokenAddress);

        // _newSaleStage(1607385600, 1607731200);
        _newSaleStage(1607428800, 1608897600);
    }

    function newSaleStage(uint _startTime, uint _finishTime) public onlyOwner {
        require(block.timestamp > sales[sales.length-1].finishTime, "wait for previous stage finish");
        _newSaleStage(_startTime, _finishTime);
    }

    receive() external payable {
        buy();
    }
    
    function buy() public payable {
        require(block.timestamp >= sales[sales.length-1].startTime, "sale is not open yet");
        require(block.timestamp < sales[sales.length-1].finishTime, "sale closed");
        require(msg.value > 0, "msg value can't be zero");

        uint forMint = msg.value*(1e18)/(ethPrice);

        token.transfer(msg.sender, forMint);
        owner.transfer(address(this).balance);
    }

    function setPrice(uint _ethPrice) public onlyOwner {
        ethPrice = _ethPrice;
    }

    function withdrawUnsoldTokens() public onlyOwner {
        require(block.timestamp > sales[sales.length-1].finishTime, "sale still open");
        token.transfer(owner, token.balanceOf(address(this)));
    }
    
    function withdraw() public onlyOwner {
        owner.transfer(address(this).balance);
    }
    
    
    function _newSaleStage(uint _startTime, uint _finishTime) internal {
        Sale memory sale = Sale({
            startTime: _startTime,
            finishTime: _finishTime
        });

        sales.push(sale);
    }
}

{
  "compilationTarget": {
    "ExseTokenSale.sol": "ExseTokenSale"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}