// SPDX-License-Identifier: CC0-1.0
// Copyright (c) 2019 Chris Haoyu LIN, Runchao HAN, Jiangshan YU
// ERC2266 is compatible with ERC20 standard: https://theethereum.wiki/w/index.php/ERC20_Token_Standard
// naming style follows the guide: https://solidity.readthedocs.io/en/v0.5.11/style-guide.html#naming-styles

pragma solidity ^0.5.11;

contract ERC20 {
    function totalSupply() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);
    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

contract Example
{
    enum AssetState { Empty, Filled, Redeemed, Refunded }

    struct Swap {
        bytes32 secretHash;
        bytes32 secret;
        address payable initiator;
        address payable participant;
        address tokenA;
        address tokenB;
    }

    struct InitiatorAsset {
        uint256 amount;
        uint256 refundTimestamp;
        AssetState state;
    }

    struct ParticipantAsset {
        uint256 amount;
        uint256 refundTimestamp;
        AssetState state;
    }

    struct Premium {
        uint256 amount;
        uint256 refundTimestamp;
        AssetState state;
    }

    mapping(bytes32 => Swap) public swap;
    mapping(bytes32 => InitiatorAsset) public initiatorAsset;
    mapping(bytes32 => ParticipantAsset) public participantAsset;
    mapping(bytes32 => Premium) public premium;

    event SetUp(
        bytes32 secretHash,
        address initiator,
        address participant,
        address tokenA,
        address tokenB,
        uint256 initiatorAssetAmount,
        uint256 participantAssetAmount,
        uint256 premiumAmount
    );

    event Initiated(
        uint256 initiateTimestamp,
        bytes32 secretHash,
        address initiator,
        address participant,
        address initiatorAssetToken,
        uint256 initiatorAssetAmount,
        uint256 initiatorAssetRefundTimestamp
    );

    event PremiumFilled(
        uint256 fillPremiumTimestamp,
        bytes32 secretHash,
        address initiator,
        address participant,
        address premiumToken,
        uint256 premiumAmount,
        uint256 premiumRefundTimestamp
    );

    event Participated(
        uint256 participateTimestamp,
        bytes32 secretHash,
        address initiator,
        address participant,
        address participantAssetToken,
        uint256 participantAssetAmount,
        uint256 participantAssetRefundTimestamp
    );

    event InitiatorAssetRedeemed(
        uint256 redeemTimestamp,
        bytes32 secretHash,
        bytes32 secret,
        address redeemer,
        address assetToken,
        uint256 amount
    );

    event ParticipantAssetRedeemed(
        uint256 redeemTimestamp,
        bytes32 secretHash,
        bytes32 secret,
        address redeemer,
        address assetToken,
        uint256 amount
    );

    event InitiatorAssetRefunded(
        uint256 refundTimestamp,
        bytes32 secretHash,
        address refunder,
        address assetToken,
        uint256 amount
    );

    event ParticipantAssetRefunded(
        uint256 refundTimestamp,
        bytes32 secretHash,
        address refunder,
        address assetToken,
        uint256 amount
    );

    event PremiumRedeemed(
        uint256 redeemTimestamp,
        bytes32 secretHash,
        address redeemer,
        address token,
        uint256 amount
    );

    event PremiumRefunded(
        uint256 refundTimestamp,
        bytes32 secretHash,
        address refunder,
        address token,
        uint256 amount
    );

    constructor() public {}

    modifier isInitiatorAssetEmptyState(bytes32 secretHash) {
        require(initiatorAsset[secretHash].state == AssetState.Empty);
        _;
    }

    modifier isParticipantAssetEmptyState(bytes32 secretHash) {
        require(participantAsset[secretHash].state == AssetState.Empty);
        _;
    }

    modifier isPremiumEmptyState(bytes32 secretHash) {
        require(premium[secretHash].state == AssetState.Empty);
        _;
    }

    modifier canSetup(bytes32 secretHash) {
        require(initiatorAsset[secretHash].state == AssetState.Empty);
        require(participantAsset[secretHash].state == AssetState.Empty);
        require(premium[secretHash].state == AssetState.Empty);
        _;
    }

    modifier canInitiate(bytes32 secretHash) {
        require(swap[secretHash].initiator == msg.sender);
        require(initiatorAsset[secretHash].state == AssetState.Empty);
        require(ERC20(swap[secretHash].tokenA).balanceOf(msg.sender) >= initiatorAsset[secretHash].amount);
        _;
    }

    modifier canFillPremium(bytes32 secretHash) {
        require(swap[secretHash].initiator == msg.sender);
        require(premium[secretHash].state == AssetState.Empty);
        require(ERC20(swap[secretHash].tokenB).balanceOf(msg.sender) >= premium[secretHash].amount);
        _;
    }

    modifier canParticipate(bytes32 secretHash) {
        require(swap[secretHash].participant == msg.sender);
        require(participantAsset[secretHash].state == AssetState.Empty);
        require(premium[secretHash].state == AssetState.Filled);
        require(ERC20(swap[secretHash].tokenB).balanceOf(msg.sender) >= participantAsset[secretHash].amount);
        _;
    }

    modifier checkRefundTimestampOverflow(uint256 refundTime) {
        uint256 refundTimestamp = block.timestamp + refundTime;
        require(refundTimestamp > block.timestamp, "calc refundTimestamp overflow");
        require(refundTimestamp > refundTime, "calc refundTimestamp overflow");
        _;
    }

    modifier isAssetRedeemable(bytes32 secretHash, bytes32 secret) {
        if (swap[secretHash].initiator == msg.sender) {
            require(initiatorAsset[secretHash].state == AssetState.Filled);
            require(block.timestamp <= initiatorAsset[secretHash].refundTimestamp);
        } else {
            require(swap[secretHash].participant == msg.sender);
            require(participantAsset[secretHash].state == AssetState.Filled);
            require(block.timestamp <= participantAsset[secretHash].refundTimestamp);
        }
        require(sha256(abi.encodePacked(secret)) == secretHash);
        _;
    }

    modifier isAssetRefundable(bytes32 secretHash) {
        if (swap[secretHash].initiator == msg.sender) {
            require(initiatorAsset[secretHash].state == AssetState.Filled);
            require(block.timestamp > initiatorAsset[secretHash].refundTimestamp);
        } else {
            require(swap[secretHash].participant == msg.sender);
            require(participantAsset[secretHash].state == AssetState.Filled);
            require(block.timestamp > participantAsset[secretHash].refundTimestamp);
        }
        _;
    }

    modifier isPremiumFilledState(bytes32 secretHash) {
        require(premium[secretHash].state == AssetState.Filled);
        _;
    }

    // Premium is redeemable for Bob if Bob participates and redeem
    // before premium's timelock expires
    modifier isPremiumRedeemable(bytes32 secretHash) {
        // the participant invokes this method to redeem the premium
        require(swap[secretHash].participant == msg.sender);
        // the premium should be deposited
        require(premium[secretHash].state == AssetState.Filled);
        // if Bob participates, which means participantAsset will be: Filled -> (Redeemed/Refunded)
        require(participantAsset[secretHash].state == AssetState.Refunded || participantAsset[secretHash].state == AssetState.Redeemed);
        // the premium timelock should not be expired
        require(block.timestamp <= premium[secretHash].refundTimestamp);
        _;
    }

    // Premium is refundable for Alice only when Alice initiates
    // but Bob does not participate after premium's timelock expires
    modifier isPremiumRefundable(bytes32 secretHash) {
        // the initiator invokes this method to refund the premium
        require(swap[secretHash].initiator == msg.sender);
        // the premium should be deposited
        require(premium[secretHash].state == AssetState.Filled);
        // asset2 should be empty
        // which means Bob does not participate
        require(participantAsset[secretHash].state == AssetState.Empty);
        require(block.timestamp > premium[secretHash].refundTimestamp);
        _;
    }

    function setup(bytes32 secretHash,
                    address payable initiator,
                    address tokenA,
                    address tokenB,
                    uint256 initiatorAssetAmount,
                    address payable participant,
                    uint256 participantAssetAmount,
                    uint256 premiumAmount)
        public
        payable
        canSetup(secretHash)
    {
        swap[secretHash].secretHash = secretHash;
        swap[secretHash].initiator = initiator;
        swap[secretHash].participant = participant;
        swap[secretHash].tokenA = tokenA;
        swap[secretHash].tokenB = tokenB;
        initiatorAsset[secretHash].amount = initiatorAssetAmount;
        initiatorAsset[secretHash].state = AssetState.Empty;
        participantAsset[secretHash].amount = participantAssetAmount;
        participantAsset[secretHash].state = AssetState.Empty;
        premium[secretHash].amount = premiumAmount;
        premium[secretHash].state = AssetState.Empty;
        
        emit SetUp(
            secretHash,
            initiator,
            participant,
            tokenA,
            tokenB,
            initiatorAssetAmount,
            participantAssetAmount,
            premiumAmount
        );
    }

    // Initiator needs to pay for the initiatorAsset(tokenA) with initiatorAssetAmount
    // Initiator will also need to call tokenA.approve(this_contract_address, initiatorAssetAmount) in advance
    function initiate(bytes32 secretHash, uint256 assetRefundTime)
        public
        payable
        canInitiate(secretHash)
        checkRefundTimestampOverflow(assetRefundTime)
    {
        ERC20(swap[secretHash].tokenA).transferFrom(swap[secretHash].initiator, address(this), initiatorAsset[secretHash].amount);
        initiatorAsset[secretHash].state = AssetState.Filled;
        initiatorAsset[secretHash].refundTimestamp = block.timestamp + assetRefundTime;
        
        emit Initiated(
            block.timestamp,
            secretHash,
            msg.sender,
            swap[secretHash].participant,
            swap[secretHash].tokenA,
            initiatorAsset[secretHash].amount,
            initiatorAsset[secretHash].refundTimestamp
        );
    }

    // Initiator needs to pay for the premium(tokenB) with premiumAmount
    // Initiator will also need to call tokenB.approve(this_contract_address, premiumAmount) in advance
    function fillPremium(bytes32 secretHash, uint256 premiumRefundTime)
        public
        payable
        canFillPremium(secretHash)
        checkRefundTimestampOverflow(premiumRefundTime)
    {   
        ERC20(swap[secretHash].tokenB).transferFrom(swap[secretHash].initiator, address(this), premium[secretHash].amount);
        premium[secretHash].state = AssetState.Filled;
        premium[secretHash].refundTimestamp = block.timestamp + premiumRefundTime;
        
        emit PremiumFilled(
            block.timestamp,
            secretHash,
            msg.sender,
            swap[secretHash].participant,
            swap[secretHash].tokenB,
            premium[secretHash].amount,
            premium[secretHash].refundTimestamp
        );
    }

    // Participant needs to pay for the participantAsset(tokenB) with participantAssetAmount
    // Participant will also need to call tokenB.approve(this_contract_address, participantAssetAmount) in advance
    function participate(bytes32 secretHash, uint256 assetRefundTime)
        public
        payable
        canParticipate(secretHash)
        checkRefundTimestampOverflow(assetRefundTime)
    {
        ERC20(swap[secretHash].tokenB).transferFrom(swap[secretHash].participant, address(this), participantAsset[secretHash].amount);
        participantAsset[secretHash].state = AssetState.Filled;
        participantAsset[secretHash].refundTimestamp = block.timestamp + assetRefundTime;        
        
        emit Participated(
            block.timestamp,
            secretHash,
            swap[secretHash].initiator,
            msg.sender,
            swap[secretHash].tokenB,
            participantAsset[secretHash].amount,
            participantAsset[secretHash].refundTimestamp
        );
    }

    function redeemAsset(bytes32 secret, bytes32 secretHash)
        public
        isAssetRedeemable(secretHash, secret)
    {
        swap[secretHash].secret = secret;
        if (swap[secretHash].initiator == msg.sender) {
            ERC20(swap[secretHash].tokenB).transfer(msg.sender, participantAsset[secretHash].amount);
            participantAsset[secretHash].state = AssetState.Redeemed;

            emit ParticipantAssetRedeemed(
                block.timestamp,
                secretHash,
                secret,
                msg.sender,
                swap[secretHash].tokenB,
                participantAsset[secretHash].amount
            );
        } else {
            ERC20(swap[secretHash].tokenA).transfer(msg.sender, initiatorAsset[secretHash].amount);
            initiatorAsset[secretHash].state = AssetState.Redeemed;

            emit InitiatorAssetRedeemed(
                block.timestamp,
                secretHash,
                secret,
                msg.sender,
                swap[secretHash].tokenA,
                initiatorAsset[secretHash].amount
            );
        }
    }

    function refundAsset(bytes32 secretHash)
        public
        isPremiumFilledState(secretHash)
        isAssetRefundable(secretHash)
    {
        if (swap[secretHash].initiator == msg.sender) {
            ERC20(swap[secretHash].tokenA).transfer(msg.sender, initiatorAsset[secretHash].amount);
            initiatorAsset[secretHash].state = AssetState.Refunded;

            emit InitiatorAssetRefunded(
                block.timestamp,
                secretHash,
                msg.sender,
                swap[secretHash].tokenA,
                initiatorAsset[secretHash].amount
            );
        } else {
            ERC20(swap[secretHash].tokenB).transfer(msg.sender, participantAsset[secretHash].amount);
            participantAsset[secretHash].state = AssetState.Refunded;

            emit ParticipantAssetRefunded(
                block.timestamp,
                secretHash,
                msg.sender,
                swap[secretHash].tokenB,
                participantAsset[secretHash].amount
            );
        }
    }

    function redeemPremium(bytes32 secretHash)
        public
        isPremiumRedeemable(secretHash)
    {
        ERC20(swap[secretHash].tokenB).transfer(msg.sender, premium[secretHash].amount);
        premium[secretHash].state = AssetState.Redeemed;

        emit PremiumRefunded(
            block.timestamp,
            swap[secretHash].secretHash,
            msg.sender,
            swap[secretHash].tokenB,
            premium[secretHash].amount
        );
    }
  
    function refundPremium(bytes32 secretHash)
        public
        isPremiumRefundable(secretHash)
    {
        ERC20(swap[secretHash].tokenB).transfer(msg.sender, premium[secretHash].amount);
        premium[secretHash].state = AssetState.Refunded;

        emit PremiumRefunded(
            block.timestamp,
            swap[secretHash].secretHash,
            msg.sender,
            swap[secretHash].tokenB,
            premium[secretHash].amount
        );
    }
}