// File: openzeppelin-solidity/contracts/token/ERC20/IERC20.sol

// 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);
}

// File: openzeppelin-solidity/contracts/math/SafeMath.sol

// SPDX-License-Identifier: MIT

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) {
        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;
    }
}

// File: openzeppelin-solidity/contracts/utils/Address.sol

// SPDX-License-Identifier: MIT

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) {
        // This method relies in extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @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 Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/SafeERC20.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;




/**
 * @title SafeERC20
 * @dev 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));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        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 safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "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");
        }
    }
}

// File: openzeppelin-solidity/contracts/introspection/IERC165.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: openzeppelin-solidity/contracts/token/ERC721/IERC721.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.2;


/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
      * @dev Safely transfers `tokenId` token from `from` to `to`.
      *
      * Requirements:
      *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
      * - `tokenId` token must exist and be owned by `from`.
      * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
      * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
      *
      * Emits a {Transfer} event.
      */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
}

// File: contracts/IQLF.sol

/**
 * @author          Yisi Liu
 * @contact         yisiliu@gmail.com
 * @author_time     01/06/2021
**/

pragma solidity >= 0.6.0;

interface IQLF {
    /**
     * @dev Returns if the given address is qualified, implemented on demand.
     */
    function ifQualified (address testee) external view returns (bool);

    /**
     * @dev Logs if the given address is qualified, implemented on demand.
     */
    function logQualified (address testee) external;

    /**
     * @dev Emit when `ifQualified` is called to decide if the given `address`
     * is `qualified` according to the preset rule by the contract creator and 
     * the current block `number` and the current block `timestamp`.
     */
    event Qualification(bool qualified, uint256 number, uint256 timestamp);
}

// File: contracts/ito.sol

/**
 * @author          Yisi Liu
 * @contact         yisiliu@gmail.com
 * @author_time     01/06/2021
**/

pragma solidity >= 0.6.0;






contract HappyTokenPool {

    struct Pool {
        uint256 packed1;            // total_address(160) hash(48) start_time_delta(24) 
                                    // expiration_time_delta(24) BIG ENDIAN
        uint256 packed2;            // total_tokens(128) limit(128)
        address creator;
        address qualification;
        address[] exchange_addrs;
        uint128[] exchanged_tokens;
        uint128[] ratios;
        mapping(address => uint256) swapped_map;
    }

    event FillSuccess (
        uint256 total,
        bytes32 id,
        address creator,
        uint256 creation_time,
        address token_address,
        string name,
        string message
    );

    event SwapSuccess (
        bytes32 id,
        address swapper,
        address from_address,
        address to_address,
        uint256 from_value,
        uint256 to_value
    );

    event DestructSuccess (
        bytes32 id,
        address token_address,
        uint256 remaining_balance,
        uint128[] exchanged_values
    );

    event WithdrawSuccess (
        bytes32 id,
        address token_address,
        uint256 withdraw_balance
    );

    using SafeERC20 for IERC20;
    uint32 nonce;
    uint256 base_timestamp;
    address public contract_creator;
    mapping(bytes32 => Pool) pool_by_id;
    string constant private magic = "Anthony Quinn Warner, 63, was identified as the bomber. Warner, \
    a 63-year-old described by one neighbor as a loner, died when his recreational vehicle exploded \
    on 2nd Avenue North in the city's downtown. The blast injured at least eight people and damaged-";
    bytes32 private seed;
    address DEFAULT_ADDRESS = 0x0000000000000000000000000000000000000000;

    constructor() public {
        contract_creator = msg.sender;
        seed = keccak256(abi.encodePacked(magic, block.timestamp, contract_creator));
        base_timestamp = 1609372800;                                    // 00:00:00 01/01/2021 GMT(UTC+0)
    }

    function fill_pool (bytes32 _hash, uint256 _start, uint256 _end, string memory name, string memory message,
                        address[] memory _exchange_addrs, uint128[] memory _ratios,
                        address _token_addr, uint256 _total_tokens, uint256 _limit, address _qualification)
    public payable {
        nonce ++;
        require(_start < _end, "Start time should be earlier than end time.");
        require(_limit <= _total_tokens, "Limit needs to be less than or equal to the total supply");
        require(_total_tokens < 2 ** 128, "No more than 2^128 tokens(incluidng decimals) allowed");
        require(IERC20(_token_addr).allowance(msg.sender, address(this)) >= _total_tokens, "Insuffcient allowance");
        require(_exchange_addrs.length > 0, "Exchange token addresses need to be set");
        require(_ratios.length == 2 * _exchange_addrs.length, "Size of ratios = 2 * size of exchange_addrs");

        bytes32 _id = keccak256(abi.encodePacked(msg.sender, block.timestamp, nonce, seed));
        Pool storage pool = pool_by_id[_id];
        pool.packed1 = wrap1(_token_addr, _hash, _start, _end);         // 256 bytes
        pool.packed2 = wrap2(_total_tokens, _limit);                    // 256 bytes
        pool.creator = msg.sender;                                      // 160 bytes
        pool.exchange_addrs = _exchange_addrs;                          // 160 bytes
        pool.qualification = _qualification;                            // 160 bytes
        for (uint256 i = 0; i < _exchange_addrs.length; i++) {
            if (_exchange_addrs[i] != DEFAULT_ADDRESS) {
                require(IERC20(_exchange_addrs[i]).totalSupply() > 0, "Not a valid ERC20");
            }
            pool.exchanged_tokens.push(0); 
        }

        for (uint256 i = 0; i < _ratios.length; i+= 2) {
            uint256 divA = SafeMath.div(_ratios[i], _ratios[i+1]);      // Non-zero checked by SafteMath.div
            uint256 divB = SafeMath.div(_ratios[i+1], _ratios[i]);
            
            if (_ratios[i] == 1) {
                require(divB == _ratios[i+1]);
            } else if (_ratios[i+1] == 1) {
                require(divA == _ratios[i]);
            } else {
                require(divA * _ratios[i+1] != _ratios[i]);
                require(divB * _ratios[i] != _ratios[i+1]);
            }
        }
        pool.ratios = _ratios;                                          // 256 * k
        IERC20(_token_addr).safeTransferFrom(msg.sender, address(this), _total_tokens);

        emit FillSuccess(_total_tokens, _id, msg.sender, block.timestamp, _token_addr, name, message);
    }

    // It takes the unhashed password and a hashed random seed generated from the user
    function swap (bytes32 id, bytes32 verification, address _recipient, 
                   bytes32 validation, uint256 exchange_addr_i, uint128 input_total) 
    public payable returns (uint256 swapped) {

        Pool storage pool = pool_by_id[id];
        address payable recipient = address(uint160(_recipient));
        require (IQLF(pool.qualification).ifQualified(msg.sender) == true, "Not Qualified");
        require (unbox(pool.packed1, 208, 24) + base_timestamp < block.timestamp, "Not started.");
        require (unbox(pool.packed1, 232, 24) + base_timestamp > block.timestamp, "Expired.");
        require (verification == keccak256(abi.encodePacked(unbox(pool.packed1, 160, 48), msg.sender)), 
                 'Wrong Password');
        require (validation == keccak256(toBytes(msg.sender)), "Validation Failed");

        uint256 total_tokens = unbox(pool.packed2, 0, 128);
        require (total_tokens > 0, "Out of Stock");

        address exchange_addr = pool.exchange_addrs[exchange_addr_i];
        uint256 ratioA = pool.ratios[exchange_addr_i*2];
        uint256 ratioB = pool.ratios[exchange_addr_i*2 + 1];
        if (exchange_addr == DEFAULT_ADDRESS) {
            require(msg.value == input_total, 'No enough ether.');
        } else {
            uint256 allowance = IERC20(exchange_addr).allowance(msg.sender, address(this));
            require(allowance >= input_total, 'No enough allowance.');
        }

        uint256 swapped_tokens;
        swapped_tokens = SafeMath.div(SafeMath.mul(input_total, ratioB), ratioA);       // 2^256=10e77 >> 10e18 * 10e18
        require(swapped_tokens > 0, "Better not draw water with a sieve");

        // Don't be greedy
        uint256 limit = unbox(pool.packed2, 128, 128);
        if (swapped_tokens > limit) {
            swapped_tokens = limit;
            input_total = uint128(SafeMath.div(SafeMath.mul(limit, ratioA), ratioB));  // Update
        } else if (swapped_tokens > total_tokens) {
            swapped_tokens = total_tokens;
            input_total = uint128(SafeMath.div(SafeMath.mul(total_tokens, ratioA), ratioB));  // Update
        }
        require(swapped_tokens <= limit);                                               // make sure
        pool.exchanged_tokens[exchange_addr_i] = uint128(SafeMath.add(pool.exchanged_tokens[exchange_addr_i], input_total));

        // Penalize greedy attackers by placing duplication check at the very last
        require (pool.swapped_map[_recipient] == 0, "Already swapped");

        pool.packed2 = rewriteBox(pool.packed2, 0, 128, SafeMath.sub(total_tokens, swapped_tokens));
        pool.swapped_map[_recipient] = swapped_tokens;

        // Transfer the token after state changing
        // ETH comes with the tx, ERC20 does not
        if (exchange_addr != DEFAULT_ADDRESS) {
            IERC20(exchange_addr).safeTransferFrom(msg.sender, address(this), input_total);
        }
        transfer_token(address(unbox(pool.packed1, 0, 160)), address(this), recipient, swapped_tokens);

        // Swap success event
        emit SwapSuccess(id, recipient, exchange_addr, address(unbox(pool.packed1, 0, 160)), 
                          input_total, swapped_tokens);
        return swapped_tokens;
    }

    // Returns 0. exchange_addrs in the given pool 1. remaining tokens 2. if expired 3. if swapped
    function check_availability (bytes32 id) external view returns (address[] memory exchange_addrs, uint256 remaining, 
                                                                    bool started, bool expired, uint256 swapped,
                                                                    uint128[] memory exchanged_tokens) {
        Pool storage pool = pool_by_id[id];
        return (
            pool.exchange_addrs,                                    // exchange_addrs if 0x0 then destructed
            unbox(pool.packed2, 0, 128),                            // remaining
            block.timestamp > unbox(pool.packed1, 208, 24) + base_timestamp,    // started
            block.timestamp > unbox(pool.packed1, 232, 24) + base_timestamp,    // expired
            pool.swapped_map[msg.sender],                           // swapped number 
            pool.exchanged_tokens                                   // exchanged tokens
        );
    }

    function destruct (bytes32 id) public {
        Pool storage pool = pool_by_id[id];
        require(msg.sender == pool.creator, "Only the pool creator can destruct.");

        address token_address = address(unbox(pool.packed1, 0, 160));
        uint256 expiration = unbox(pool.packed1, 232, 24) + base_timestamp;
        uint256 remaining_tokens = unbox(pool.packed2, 0, 128);
        require(expiration <= block.timestamp || remaining_tokens == 0, "Not expired yet");

        if (remaining_tokens != 0) {
            transfer_token(token_address, address(this), msg.sender, remaining_tokens);
        }

        for (uint256 i = 0; i < pool.exchange_addrs.length; i++) {
            if (pool.exchanged_tokens[i] > 0) {
                if (pool.exchange_addrs[i] != DEFAULT_ADDRESS)
                    transfer_token(pool.exchange_addrs[i], address(this), msg.sender, pool.exchanged_tokens[i]);
                else
                    msg.sender.transfer(pool.exchanged_tokens[i]);
            }
        }
        emit DestructSuccess(id, token_address, remaining_tokens, pool.exchanged_tokens);

        // Gas Refund
        pool.packed1 = 0;
        pool.packed2 = 0;
        pool.creator = DEFAULT_ADDRESS;
        for (uint256 i = 0; i < pool.exchange_addrs.length; i++) {
            pool.exchange_addrs[i] = DEFAULT_ADDRESS;
            pool.exchanged_tokens[i] = 0;
            pool.ratios[i*2] = 0;
            pool.ratios[i*2+1] = 0;
        }
    }

    function withdraw (bytes32 id, uint256 addr_i) public {
        Pool storage pool = pool_by_id[id];
        require(msg.sender == pool.creator, "Only the pool creator can withdraw.");

        uint256 withdraw_balance = pool.exchanged_tokens[addr_i];
        require(withdraw_balance > 0, "None of this token left");
        uint256 expiration = unbox(pool.packed1, 232, 24) + base_timestamp;
        uint256 remaining_tokens = unbox(pool.packed2, 0, 128);
        require(expiration <= block.timestamp || remaining_tokens == 0, "Not expired yet");
        address token_address = pool.exchange_addrs[addr_i];

        if (token_address != DEFAULT_ADDRESS)
            transfer_token(token_address, address(this), msg.sender, withdraw_balance);
        else
            msg.sender.transfer(withdraw_balance);
        pool.exchanged_tokens[addr_i] = 0;
        emit WithdrawSuccess(id, token_address, withdraw_balance);
    }

    // helper functions
    function wrap1 (address _token_addr, bytes32 _hash, uint256 _start, uint256 _end) internal pure 
                    returns (uint256 packed1) {
        uint256 _packed1 = 0;
        _packed1 |= box(0, 160,  uint256(_token_addr));     // token_addr = 160 bits
        _packed1 |= box(160, 48, uint256(_hash) >> 208);    // hash = 48 bits (safe?)
        _packed1 |= box(208, 24, _start);                   // start_time = 24 bits 
        _packed1 |= box(232, 24, _end);                     // expiration_time = 24 bits
        return _packed1;
    }

    function wrap2 (uint256 _total_tokens, uint256 _limit) internal pure returns (uint256 packed2) {
        uint256 _packed2 = 0;
        _packed2 |= box(0, 128, _total_tokens);             // total_tokens = 128 bits ~= 3.4e38
        _packed2 |= box(128, 128, _limit);                  // limit = 128 bits
        return _packed2;
    }

    function box (uint16 position, uint16 size, uint256 data) internal pure returns (uint256 boxed) {
        require(validRange(size, data), "Value out of range BOX");
        return data << (256 - size - position);
    }

    function unbox (uint256 base, uint16 position, uint16 size) internal pure returns (uint256 unboxed) {
        require(validRange(256, base), "Value out of range UNBOX");
        return (base << position) >> (256 - size);
    }

    function validRange (uint16 size, uint256 data) internal pure returns(bool) { 
        if (data > 2 ** uint256(size) - 1) {
            return false;
        }
        return true;
    }

    function rewriteBox (uint256 _box, uint16 position, uint16 size, uint256 data) 
    internal pure returns (uint256 boxed) {
        uint256 _boxData = box(position, size, data);
        uint256 _mask = box(position, size, uint256(-1) >> (256 - size));
        _box = (_box & ~_mask) | _boxData;
        return _box;
    }

    function transfer_token (address token_address, address sender_address,
                             address recipient_address, uint256 amount) internal {
        require(IERC20(token_address).balanceOf(sender_address) >= amount, "Balance not enough");
        IERC20(token_address).safeTransfer(recipient_address, amount);
    }
    
    // https://ethereum.stackexchange.com/questions/884/how-to-convert-an-address-to-bytes-in-solidity
    // 695 gas consumed
    function toBytes (address a) internal pure returns (bytes memory b) {
        assembly {
            let m := mload(0x40)
            a := and(a, 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)
            mstore(add(m, 20), xor(0x140000000000000000000000000000000000000000, a))
            mstore(0x40, add(m, 52))
            b := m
        }
    }
}