// File: contracts/contracts/core/lock_proxy/LockProxy.sol



pragma solidity ^0.5.0;

import "./../../libs/ownership/Ownable.sol";
import "./../../libs/common/ZeroCopySource.sol";
import "./../../libs/common/ZeroCopySink.sol";
import "./../../libs/utils/Utils.sol";
import "./../../libs/token/ERC20/SafeERC20.sol";
import "./../cross_chain_manager/interface/IEthCrossChainManager.sol";
import "./../cross_chain_manager/interface/IEthCrossChainManagerProxy.sol";


contract LockProxy is Ownable {
    using SafeMath for uint;
    using SafeERC20 for IERC20;

    struct TxArgs {
        bytes toAssetHash;
        bytes toAddress;
        uint256 amount;
    }
    address public managerProxyContract;
    mapping(uint64 => bytes) public proxyHashMap;
    mapping(address => mapping(uint64 => bytes)) public assetHashMap;
    mapping(address => bool) safeTransfer;

    event SetManagerProxyEvent(address manager);
    event BindProxyEvent(uint64 toChainId, bytes targetProxyHash);
    event BindAssetEvent(address fromAssetHash, uint64 toChainId, bytes targetProxyHash, uint initialAmount);
    event UnlockEvent(address toAssetHash, address toAddress, uint256 amount);
    event LockEvent(address fromAssetHash, address fromAddress, uint64 toChainId, bytes toAssetHash, bytes toAddress, uint256 amount);
    
    modifier onlyManagerContract() {
        IEthCrossChainManagerProxy ieccmp = IEthCrossChainManagerProxy(managerProxyContract);
        require(_msgSender() == ieccmp.getEthCrossChainManager(), "msgSender is not EthCrossChainManagerContract");
        _;
    }
    
    function setManagerProxy(address ethCCMProxyAddr) onlyOwner public {
        managerProxyContract = ethCCMProxyAddr;
        emit SetManagerProxyEvent(managerProxyContract);
    }
    
    function bindProxyHash(uint64 toChainId, bytes memory targetProxyHash) onlyOwner public returns (bool) {
        proxyHashMap[toChainId] = targetProxyHash;
        emit BindProxyEvent(toChainId, targetProxyHash);
        return true;
    }
    
    function bindAssetHash(address fromAssetHash, uint64 toChainId, bytes memory toAssetHash) onlyOwner public returns (bool) {
        assetHashMap[fromAssetHash][toChainId] = toAssetHash;
        emit BindAssetEvent(fromAssetHash, toChainId, toAssetHash, getBalanceFor(fromAssetHash));
        return true;
    }
    
    /* @notice                  This function is meant to be invoked by the user,
    *                           a certin amount teokens will be locked in the proxy contract the invoker/msg.sender immediately.
    *                           Then the same amount of tokens will be unloked from target chain proxy contract at the target chain with chainId later.
    *  @param fromAssetHash     The asset address in current chain, uniformly named as `fromAssetHash`
    *  @param toChainId         The target chain id
    *                           
    *  @param toAddress         The address in bytes format to receive same amount of tokens in target chain 
    *  @param amount            The amount of tokens to be crossed from ethereum to the chain with chainId
    */
    function lock(address fromAssetHash, uint64 toChainId, bytes memory toAddress, uint256 amount) public payable returns (bool) {
        require(amount != 0, "amount cannot be zero!");
        
        
        require(_transferToContract(fromAssetHash, amount), "transfer asset from fromAddress to lock_proxy contract  failed!");
        
        bytes memory toAssetHash = assetHashMap[fromAssetHash][toChainId];
        require(toAssetHash.length != 0, "empty illegal toAssetHash");

        TxArgs memory txArgs = TxArgs({
            toAssetHash: toAssetHash,
            toAddress: toAddress,
            amount: amount
        });
        bytes memory txData = _serializeTxArgs(txArgs);
        
        IEthCrossChainManagerProxy eccmp = IEthCrossChainManagerProxy(managerProxyContract);
        address eccmAddr = eccmp.getEthCrossChainManager();
        IEthCrossChainManager eccm = IEthCrossChainManager(eccmAddr);
        
        bytes memory toProxyHash = proxyHashMap[toChainId];
        require(toProxyHash.length != 0, "empty illegal toProxyHash");
        require(eccm.crossChain(toChainId, toProxyHash, "unlock", txData), "EthCrossChainManager crossChain executed error!");

        emit LockEvent(fromAssetHash, _msgSender(), toChainId, toAssetHash, toAddress, amount);
        
        return true;

    }
    
    // /* @notice                  This function is meant to be invoked by the ETH crosschain management contract,
    // *                           then mint a certin amount of tokens to the designated address since a certain amount 
    // *                           was burnt from the source chain invoker.
    // *  @param argsBs            The argument bytes recevied by the ethereum lock proxy contract, need to be deserialized.
    // *                           based on the way of serialization in the source chain proxy contract.
    // *  @param fromContractAddr  The source chain contract address
    // *  @param fromChainId       The source chain id
    // */
    function unlock(bytes memory argsBs, bytes memory fromContractAddr, uint64 fromChainId) onlyManagerContract public returns (bool) {
        TxArgs memory args = _deserializeTxArgs(argsBs);

        require(fromContractAddr.length != 0, "from proxy contract address cannot be empty");
        require(Utils.equalStorage(proxyHashMap[fromChainId], fromContractAddr), "From Proxy contract address error!");
        
        require(args.toAssetHash.length != 0, "toAssetHash cannot be empty");
        address toAssetHash = Utils.bytesToAddress(args.toAssetHash);

        require(args.toAddress.length != 0, "toAddress cannot be empty");
        address toAddress = Utils.bytesToAddress(args.toAddress);
        
        
        require(_transferFromContract(toAssetHash, toAddress, args.amount), "transfer asset from lock_proxy contract to toAddress failed!");
        
        emit UnlockEvent(toAssetHash, toAddress, args.amount);
        return true;
    }
    
    function getBalanceFor(address fromAssetHash) public view returns (uint256) {
        if (fromAssetHash == address(0)) {
            // return address(this).balance; // this expression would result in error: Failed to decode output: Error: insufficient data for uint256 type
            address selfAddr = address(this);
            return selfAddr.balance;
        } else {
            IERC20 erc20Token = IERC20(fromAssetHash);
            return erc20Token.balanceOf(address(this));
        }
    }
    function _transferToContract(address fromAssetHash, uint256 amount) internal returns (bool) {
        if (fromAssetHash == address(0)) {
            // fromAssetHash === address(0) denotes user choose to lock ether
            // passively check if the received msg.value equals amount
            require(msg.value != 0, "transferred ether cannot be zero!");
            require(msg.value == amount, "transferred ether is not equal to amount!");
        } else {
            // make sure lockproxy contract will decline any received ether
            require(msg.value == 0, "there should be no ether transfer!");
            // actively transfer amount of asset from msg.sender to lock_proxy contract
            require(_transferERC20ToContract(fromAssetHash, _msgSender(), address(this), amount), "transfer erc20 asset to lock_proxy contract failed!");
        }
        return true;
    }
    function _transferFromContract(address toAssetHash, address toAddress, uint256 amount) internal returns (bool) {
        if (toAssetHash == address(0x0000000000000000000000000000000000000000)) {
            // toAssetHash === address(0) denotes contract needs to unlock ether to toAddress
            // convert toAddress from 'address' type to 'address payable' type, then actively transfer ether
            address(uint160(toAddress)).transfer(amount);
        } else {
            // actively transfer amount of asset from lock_proxy contract to toAddress
            require(_transferERC20FromContract(toAssetHash, toAddress, amount), "transfer erc20 asset from lock_proxy contract to toAddress failed!");
        }
        return true;
    }
    
    
    function _transferERC20ToContract(address fromAssetHash, address fromAddress, address toAddress, uint256 amount) internal returns (bool) {
         IERC20 erc20Token = IERC20(fromAssetHash);
        //  require(erc20Token.transferFrom(fromAddress, toAddress, amount), "trasnfer ERC20 Token failed!");
         erc20Token.safeTransferFrom(fromAddress, toAddress, amount);
         return true;
    }
    function _transferERC20FromContract(address toAssetHash, address toAddress, uint256 amount) internal returns (bool) {
         IERC20 erc20Token = IERC20(toAssetHash);
        //  require(erc20Token.transfer(toAddress, amount), "trasnfer ERC20 Token failed!");
         erc20Token.safeTransfer(toAddress, amount);
         return true;
    }
    
    function _serializeTxArgs(TxArgs memory args) internal pure returns (bytes memory) {
        bytes memory buff;
        buff = abi.encodePacked(
            ZeroCopySink.WriteVarBytes(args.toAssetHash),
            ZeroCopySink.WriteVarBytes(args.toAddress),
            ZeroCopySink.WriteUint255(args.amount)
            );
        return buff;
    }

    function _deserializeTxArgs(bytes memory valueBs) internal pure returns (TxArgs memory) {
        TxArgs memory args;
        uint256 off = 0;
        (args.toAssetHash, off) = ZeroCopySource.NextVarBytes(valueBs, off);
        (args.toAddress, off) = ZeroCopySource.NextVarBytes(valueBs, off);
        (args.amount, off) = ZeroCopySource.NextUint255(valueBs, off);
        return args;
    }
}
// File: contracts/contracts/core/cross_chain_manager/interface/IEthCrossChainManagerProxy.sol



pragma solidity ^0.5.0;

/**
 * @dev Interface of the EthCrossChainManagerProxy for business contract like LockProxy to obtain the reliable EthCrossChainManager contract hash.
 */
interface IEthCrossChainManagerProxy {
    function getEthCrossChainManager() external view returns (address);
}

// File: contracts/contracts/core/cross_chain_manager/interface/IEthCrossChainManager.sol



pragma solidity ^0.5.0;

/**
 * @dev Interface of the EthCrossChainManager contract for business contract like LockProxy to request cross chain transaction
 */
interface IEthCrossChainManager {
    function crossChain(uint64 _toChainId, bytes calldata _toContract, bytes calldata _method, bytes calldata _txData) external returns (bool);
}

// File: contracts/contracts/libs/token/ERC20/SafeERC20.sol



pragma solidity ^0.5.0;

import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Utils.sol";

/**
 * @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 ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;

    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));
    }

    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);
        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.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        require(Utils.isContract(address(token)), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "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: contracts/contracts/libs/utils/Utils.sol



pragma solidity ^0.5.0;


library Utils {

    /* @notice      Convert the bytes array to bytes32 type, the bytes array length must be 32
    *  @param _bs   Source bytes array
    *  @return      bytes32
    */
    function bytesToBytes32(bytes memory _bs) internal pure returns (bytes32 value) {
        require(_bs.length == 32, "bytes length is not 32.");
        assembly {
            // load 32 bytes from memory starting from position _bs + 0x20 since the first 0x20 bytes stores _bs length
            value := mload(add(_bs, 0x20))
        }
    }

    /* @notice      Convert bytes to uint256
    *  @param _b    Source bytes should have length of 32
    *  @return      uint256
    */
    function bytesToUint256(bytes memory _bs) internal pure returns (uint256 value) {
        require(_bs.length == 32, "bytes length is not 32.");
        assembly {
            // load 32 bytes from memory starting from position _bs + 32
            value := mload(add(_bs, 0x20))
        }
        require(value <= 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, "Value exceeds the range");
    }

    /* @notice      Convert uint256 to bytes
    *  @param _b    uint256 that needs to be converted
    *  @return      bytes
    */
    function uint256ToBytes(uint256 _value) internal pure returns (bytes memory bs) {
        require(_value <= 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, "Value exceeds the range");
        assembly {
            // Get a location of some free memory and store it in result as
            // Solidity does for memory variables.
            bs := mload(0x40)
            // Put 0x20 at the first word, the length of bytes for uint256 value
            mstore(bs, 0x20)
            //In the next word, put value in bytes format to the next 32 bytes
            mstore(add(bs, 0x20), _value)
            // Update the free-memory pointer by padding our last write location to 32 bytes
            mstore(0x40, add(bs, 0x40))
        }
    }

    /* @notice      Convert bytes to address
    *  @param _bs   Source bytes: bytes length must be 20
    *  @return      Converted address from source bytes
    */
    function bytesToAddress(bytes memory _bs) internal pure returns (address addr)
    {
        require(_bs.length == 20, "bytes length does not match address");
        assembly {
            // for _bs, first word store _bs.length, second word store _bs.value
            // load 32 bytes from mem[_bs+20], convert it into Uint160, meaning we take last 20 bytes as addr (address).
            addr := mload(add(_bs, 0x14))
        }

    }
    
    /* @notice      Convert address to bytes
    *  @param _addr Address need to be converted
    *  @return      Converted bytes from address
    */
    function addressToBytes(address _addr) internal pure returns (bytes memory bs){
        assembly {
            // Get a location of some free memory and store it in result as
            // Solidity does for memory variables.
            bs := mload(0x40)
            // Put 20 (address byte length) at the first word, the length of bytes for uint256 value
            mstore(bs, 0x14)
            // logical shift left _a by 12 bytes, change _a from right-aligned to left-aligned
            mstore(add(bs, 0x20), shl(96, _addr))
            // Update the free-memory pointer by padding our last write location to 32 bytes
            mstore(0x40, add(bs, 0x40))
       }
    }

    /* @notice          Do hash leaf as the multi-chain does
    *  @param _data     Data in bytes format
    *  @return          Hashed value in bytes32 format
    */
    function hashLeaf(bytes memory _data) internal pure returns (bytes32 result)  {
        result = sha256(abi.encodePacked(byte(0x0), _data));
    }

    /* @notice          Do hash children as the multi-chain does
    *  @param _l        Left node
    *  @param _r        Right node
    *  @return          Hashed value in bytes32 format
    */
    function hashChildren(bytes32 _l, bytes32  _r) internal pure returns (bytes32 result)  {
        result = sha256(abi.encodePacked(bytes1(0x01), _l, _r));
    }

    /* @notice              Compare if two bytes are equal, which are in storage and memory, seperately
                            Refer from https://github.com/summa-tx/bitcoin-spv/blob/master/solidity/contracts/BytesLib.sol#L368
    *  @param _preBytes     The bytes stored in storage
    *  @param _postBytes    The bytes stored in memory
    *  @return              Bool type indicating if they are equal
    */
    function equalStorage(bytes storage _preBytes, bytes memory _postBytes) internal view returns (bool) {
        bool success = true;

        assembly {
            // we know _preBytes_offset is 0
            let fslot := sload(_preBytes_slot)
            // Arrays of 31 bytes or less have an even value in their slot,
            // while longer arrays have an odd value. The actual length is
            // the slot divided by two for odd values, and the lowest order
            // byte divided by two for even values.
            // If the slot is even, bitwise and the slot with 255 and divide by
            // two to get the length. If the slot is odd, bitwise and the slot
            // with -1 and divide by two.
            let slength := div(and(fslot, sub(mul(0x100, iszero(and(fslot, 1))), 1)), 2)
            let mlength := mload(_postBytes)

            // if lengths don't match the arrays are not equal
            switch eq(slength, mlength)
            case 1 {
                // fslot can contain both the length and contents of the array
                // if slength < 32 bytes so let's prepare for that
                // v. http://solidity.readthedocs.io/en/latest/miscellaneous.html#layout-of-state-variables-in-storage
                // slength != 0
                if iszero(iszero(slength)) {
                    switch lt(slength, 32)
                    case 1 {
                        // blank the last byte which is the length
                        fslot := mul(div(fslot, 0x100), 0x100)

                        if iszero(eq(fslot, mload(add(_postBytes, 0x20)))) {
                            // unsuccess:
                            success := 0
                        }
                    }
                    default {
                        // cb is a circuit breaker in the for loop since there's
                        //  no said feature for inline assembly loops
                        // cb = 1 - don't breaker
                        // cb = 0 - break
                        let cb := 1

                        // get the keccak hash to get the contents of the array
                        mstore(0x0, _preBytes_slot)
                        let sc := keccak256(0x0, 0x20)

                        let mc := add(_postBytes, 0x20)
                        let end := add(mc, mlength)

                        // the next line is the loop condition:
                        // while(uint(mc < end) + cb == 2)
                        for {} eq(add(lt(mc, end), cb), 2) {
                            sc := add(sc, 1)
                            mc := add(mc, 0x20)
                        } {
                            if iszero(eq(sload(sc), mload(mc))) {
                                // unsuccess:
                                success := 0
                                cb := 0
                            }
                        }
                    }
                }
            }
            default {
                // unsuccess:
                success := 0
            }
        }

        return success;
    }

    /* @notice              Slice the _bytes from _start index till the result has length of _length
                            Refer from https://github.com/summa-tx/bitcoin-spv/blob/master/solidity/contracts/BytesLib.sol#L246
    *  @param _bytes        The original bytes needs to be sliced
    *  @param _start        The index of _bytes for the start of sliced bytes
    *  @param _length       The index of _bytes for the end of sliced bytes
    *  @return              The sliced bytes
    */
    function slice(
        bytes memory _bytes,
        uint _start,
        uint _length
    )
        internal
        pure
        returns (bytes memory)
    {
        require(_bytes.length >= (_start + _length));

        bytes memory tempBytes;

        assembly {
            switch iszero(_length)
            case 0 {
                // Get a location of some free memory and store it in tempBytes as
                // Solidity does for memory variables.
                tempBytes := mload(0x40)

                // The first word of the slice result is potentially a partial
                // word read from the original array. To read it, we calculate
                // the length of that partial word and start copying that many
                // bytes into the array. The first word we copy will start with
                // data we don't care about, but the last `lengthmod` bytes will
                // land at the beginning of the contents of the new array. When
                // we're done copying, we overwrite the full first word with
                // the actual length of the slice.
                // lengthmod <= _length % 32
                let lengthmod := and(_length, 31)

                // The multiplication in the next line is necessary
                // because when slicing multiples of 32 bytes (lengthmod == 0)
                // the following copy loop was copying the origin's length
                // and then ending prematurely not copying everything it should.
                let mc := add(add(tempBytes, lengthmod), mul(0x20, iszero(lengthmod)))
                let end := add(mc, _length)

                for {
                    // The multiplication in the next line has the same exact purpose
                    // as the one above.
                    let cc := add(add(add(_bytes, lengthmod), mul(0x20, iszero(lengthmod))), _start)
                } lt(mc, end) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    mstore(mc, mload(cc))
                }

                mstore(tempBytes, _length)

                //update free-memory pointer
                //allocating the array padded to 32 bytes like the compiler does now
                mstore(0x40, and(add(mc, 31), not(31)))
            }
            //if we want a zero-length slice let's just return a zero-length array
            default {
                tempBytes := mload(0x40)

                mstore(0x40, add(tempBytes, 0x20))
            }
        }

        return tempBytes;
    }
    /* @notice              Check if the elements number of _signers within _keepers array is no less than _m
    *  @param _keepers      The array consists of serveral address
    *  @param _signers      Some specific addresses to be looked into
    *  @param _m            The number requirement paramter
    *  @return              True means containment, false meansdo do not contain.
    */
    function containMAddresses(address[] memory _keepers, address[] memory _signers, uint _m) internal pure returns (bool){
        uint m = 0;
        for(uint i = 0; i < _signers.length; i++){
            for (uint j = 0; j < _keepers.length; j++) {
                if (_signers[i] == _keepers[j]) {
                    m++;
                    // delete _keepers[j];
                    _keepers[j] = 0x7777777777777777777777777777777777777777;
                }
            }
        }
        return m >= _m;
    }

    /* @notice              TODO
    *  @param key
    *  @return
    */
    function compressMCPubKey(bytes memory key) internal pure returns (bytes memory newkey) {
         require(key.length >= 67, "key lenggh is too short");
         newkey = slice(key, 0, 35);
         if (uint8(key[66]) % 2 == 0){
             newkey[2] = byte(0x02);
         } else {
             newkey[2] = byte(0x03);
         }
         return newkey;
    }
    
    /**
     * @dev Returns true if `account` is a contract.
     *      Refer from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Address.sol#L18
     *
     * This test is non-exhaustive, and there may be false-negatives: during the
     * execution of a contract's constructor, its address will be reported as
     * not containing 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.
     */
    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.

        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != 0x0 && codehash != accountHash);
    }
}
// File: contracts/contracts/libs/common/ZeroCopySink.sol



pragma solidity ^0.5.0;

/**
 * @dev Wrappers over encoding and serialization operation into bytes from bassic types in Solidity for PolyNetwork cross chain utility.
 *
 * Encode basic types in Solidity into bytes easily. It's designed to be used 
 * for PolyNetwork cross chain application, and the encoding rules on Ethereum chain 
 * and the decoding rules on other chains should be consistent. Here we  
 * follow the underlying serialization rule with implementation found here: 
 * https://github.com/polynetwork/poly/blob/master/common/zero_copy_sink.go
 *
 * Using this library instead of the unchecked serialization method can help reduce
 * the risk of serious bugs and handfule, so it's recommended to use it.
 *
 * Please note that risk can be minimized, yet not eliminated.
 */
library ZeroCopySink {
    /* @notice          Convert boolean value into bytes
    *  @param b         The boolean value
    *  @return          Converted bytes array
    */
    function WriteBool(bool b) internal pure returns (bytes memory) {
        bytes memory buff;
        assembly{
            buff := mload(0x40)
            mstore(buff, 1)
            switch iszero(b)
            case 1 {
                mstore(add(buff, 0x20), shl(248, 0x00))
                // mstore8(add(buff, 0x20), 0x00)
            }
            default {
                mstore(add(buff, 0x20), shl(248, 0x01))
                // mstore8(add(buff, 0x20), 0x01)
            }
            mstore(0x40, add(buff, 0x21))
        }
        return buff;
    }

    /* @notice          Convert byte value into bytes
    *  @param b         The byte value
    *  @return          Converted bytes array
    */
    function WriteByte(byte b) internal pure returns (bytes memory) {
        return WriteUint8(uint8(b));
    }

    /* @notice          Convert uint8 value into bytes
    *  @param v         The uint8 value
    *  @return          Converted bytes array
    */
    function WriteUint8(uint8 v) internal pure returns (bytes memory) {
        bytes memory buff;
        assembly{
            buff := mload(0x40)
            mstore(buff, 1)
            mstore(add(buff, 0x20), shl(248, v))
            // mstore(add(buff, 0x20), byte(0x1f, v))
            mstore(0x40, add(buff, 0x21))
        }
        return buff;
    }

    /* @notice          Convert uint16 value into bytes
    *  @param v         The uint16 value
    *  @return          Converted bytes array
    */
    function WriteUint16(uint16 v) internal pure returns (bytes memory) {
        bytes memory buff;

        assembly{
            buff := mload(0x40)
            let byteLen := 0x02
            mstore(buff, byteLen)
            for {
                let mindex := 0x00
                let vindex := 0x1f
            } lt(mindex, byteLen) {
                mindex := add(mindex, 0x01)
                vindex := sub(vindex, 0x01)
            }{
                mstore8(add(add(buff, 0x20), mindex), byte(vindex, v))
            }
            mstore(0x40, add(buff, 0x22))
        }
        return buff;
    }
    
    /* @notice          Convert uint32 value into bytes
    *  @param v         The uint32 value
    *  @return          Converted bytes array
    */
    function WriteUint32(uint32 v) internal pure returns(bytes memory) {
        bytes memory buff;
        assembly{
            buff := mload(0x40)
            let byteLen := 0x04
            mstore(buff, byteLen)
            for {
                let mindex := 0x00
                let vindex := 0x1f
            } lt(mindex, byteLen) {
                mindex := add(mindex, 0x01)
                vindex := sub(vindex, 0x01)
            }{
                mstore8(add(add(buff, 0x20), mindex), byte(vindex, v))
            }
            mstore(0x40, add(buff, 0x24))
        }
        return buff;
    }

    /* @notice          Convert uint64 value into bytes
    *  @param v         The uint64 value
    *  @return          Converted bytes array
    */
    function WriteUint64(uint64 v) internal pure returns(bytes memory) {
        bytes memory buff;

        assembly{
            buff := mload(0x40)
            let byteLen := 0x08
            mstore(buff, byteLen)
            for {
                let mindex := 0x00
                let vindex := 0x1f
            } lt(mindex, byteLen) {
                mindex := add(mindex, 0x01)
                vindex := sub(vindex, 0x01)
            }{
                mstore8(add(add(buff, 0x20), mindex), byte(vindex, v))
            }
            mstore(0x40, add(buff, 0x28))
        }
        return buff;
    }

    /* @notice          Convert limited uint256 value into bytes
    *  @param v         The uint256 value
    *  @return          Converted bytes array
    */
    function WriteUint255(uint256 v) internal pure returns (bytes memory) {
        require(v <= 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, "Value exceeds uint255 range");
        bytes memory buff;

        assembly{
            buff := mload(0x40)
            let byteLen := 0x20
            mstore(buff, byteLen)
            for {
                let mindex := 0x00
                let vindex := 0x1f
            } lt(mindex, byteLen) {
                mindex := add(mindex, 0x01)
                vindex := sub(vindex, 0x01)
            }{
                mstore8(add(add(buff, 0x20), mindex), byte(vindex, v))
            }
            mstore(0x40, add(buff, 0x40))
        }
        return buff;
    }

    /* @notice          Encode bytes format data into bytes
    *  @param data      The bytes array data
    *  @return          Encoded bytes array
    */
    function WriteVarBytes(bytes memory data) internal pure returns (bytes memory) {
        uint64 l = uint64(data.length);
        return abi.encodePacked(WriteVarUint(l), data);
    }

    function WriteVarUint(uint64 v) internal pure returns (bytes memory) {
        if (v < 0xFD){
    		return WriteUint8(uint8(v));
    	} else if (v <= 0xFFFF) {
    		return abi.encodePacked(WriteByte(0xFD), WriteUint16(uint16(v)));
    	} else if (v <= 0xFFFFFFFF) {
            return abi.encodePacked(WriteByte(0xFE), WriteUint32(uint32(v)));
    	} else {
    		return abi.encodePacked(WriteByte(0xFF), WriteUint64(uint64(v)));
    	}
    }
}
// File: contracts/contracts/libs/common/ZeroCopySource.sol



pragma solidity ^0.5.0;

/**
 * @dev Wrappers over decoding and deserialization operation from bytes into bassic types in Solidity for PolyNetwork cross chain utility.
 *
 * Decode into basic types in Solidity from bytes easily. It's designed to be used 
 * for PolyNetwork cross chain application, and the decoding rules on Ethereum chain 
 * and the encoding rule on other chains should be consistent, and . Here we
 * follow the underlying deserialization rule with implementation found here: 
 * https://github.com/polynetwork/poly/blob/master/common/zero_copy_source.go
 *
 * Using this library instead of the unchecked serialization method can help reduce
 * the risk of serious bugs and handfule, so it's recommended to use it.
 *
 * Please note that risk can be minimized, yet not eliminated.
 */
library ZeroCopySource {
    /* @notice              Read next byte as boolean type starting at offset from buff
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the boolean value
    *  @return              The the read boolean value and new offset
    */
    function NextBool(bytes memory buff, uint256 offset) internal pure returns(bool, uint256) {
        require(offset + 1 <= buff.length && offset < offset + 1, "Offset exceeds limit");
        // byte === bytes1
        byte v;
        assembly{
            v := mload(add(add(buff, 0x20), offset))
        }
        bool value;
        if (v == 0x01) {
		    value = true;
    	} else if (v == 0x00) {
            value = false;
        } else {
            revert("NextBool value error");
        }
        return (value, offset + 1);
    }

    /* @notice              Read next byte starting at offset from buff
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the byte value
    *  @return              The read byte value and new offset
    */
    function NextByte(bytes memory buff, uint256 offset) internal pure returns (byte, uint256) {
        require(offset + 1 <= buff.length && offset < offset + 1, "NextByte, Offset exceeds maximum");
        byte v;
        assembly{
            v := mload(add(add(buff, 0x20), offset))
        }
        return (v, offset + 1);
    }

    /* @notice              Read next byte as uint8 starting at offset from buff
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the byte value
    *  @return              The read uint8 value and new offset
    */
    function NextUint8(bytes memory buff, uint256 offset) internal pure returns (uint8, uint256) {
        require(offset + 1 <= buff.length && offset < offset + 1, "NextUint8, Offset exceeds maximum");
        uint8 v;
        assembly{
            let tmpbytes := mload(0x40)
            let bvalue := mload(add(add(buff, 0x20), offset))
            mstore8(tmpbytes, byte(0, bvalue))
            mstore(0x40, add(tmpbytes, 0x01))
            v := mload(sub(tmpbytes, 0x1f))
        }
        return (v, offset + 1);
    }

    /* @notice              Read next two bytes as uint16 type starting from offset
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the uint16 value
    *  @return              The read uint16 value and updated offset
    */
    function NextUint16(bytes memory buff, uint256 offset) internal pure returns (uint16, uint256) {
        require(offset + 2 <= buff.length && offset < offset + 2, "NextUint16, offset exceeds maximum");
        
        uint16 v;
        assembly {
            let tmpbytes := mload(0x40)
            let bvalue := mload(add(add(buff, 0x20), offset))
            mstore8(tmpbytes, byte(0x01, bvalue))
            mstore8(add(tmpbytes, 0x01), byte(0, bvalue))
            mstore(0x40, add(tmpbytes, 0x02))
            v := mload(sub(tmpbytes, 0x1e))
        }
        return (v, offset + 2);
    }


    /* @notice              Read next four bytes as uint32 type starting from offset
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the uint32 value
    *  @return              The read uint32 value and updated offset
    */
    function NextUint32(bytes memory buff, uint256 offset) internal pure returns (uint32, uint256) {
        require(offset + 4 <= buff.length && offset < offset + 4, "NextUint32, offset exceeds maximum");
        uint32 v;
        assembly {
            let tmpbytes := mload(0x40)
            let byteLen := 0x04
            for {
                let tindex := 0x00
                let bindex := sub(byteLen, 0x01)
                let bvalue := mload(add(add(buff, 0x20), offset))
            } lt(tindex, byteLen) {
                tindex := add(tindex, 0x01)
                bindex := sub(bindex, 0x01)
            }{
                mstore8(add(tmpbytes, tindex), byte(bindex, bvalue))
            }
            mstore(0x40, add(tmpbytes, byteLen))
            v := mload(sub(tmpbytes, sub(0x20, byteLen)))
        }
        return (v, offset + 4);
    }

    /* @notice              Read next eight bytes as uint64 type starting from offset
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the uint64 value
    *  @return              The read uint64 value and updated offset
    */
    function NextUint64(bytes memory buff, uint256 offset) internal pure returns (uint64, uint256) {
        require(offset + 8 <= buff.length && offset < offset + 8, "NextUint64, offset exceeds maximum");
        uint64 v;
        assembly {
            let tmpbytes := mload(0x40)
            let byteLen := 0x08
            for {
                let tindex := 0x00
                let bindex := sub(byteLen, 0x01)
                let bvalue := mload(add(add(buff, 0x20), offset))
            } lt(tindex, byteLen) {
                tindex := add(tindex, 0x01)
                bindex := sub(bindex, 0x01)
            }{
                mstore8(add(tmpbytes, tindex), byte(bindex, bvalue))
            }
            mstore(0x40, add(tmpbytes, byteLen))
            v := mload(sub(tmpbytes, sub(0x20, byteLen)))
        }
        return (v, offset + 8);
    }

    /* @notice              Read next 32 bytes as uint256 type starting from offset,
                            there are limits considering the numerical limits in multi-chain
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the uint256 value
    *  @return              The read uint256 value and updated offset
    */
    function NextUint255(bytes memory buff, uint256 offset) internal pure returns (uint256, uint256) {
        require(offset + 32 <= buff.length && offset < offset + 32, "NextUint255, offset exceeds maximum");
        uint256 v;
        assembly {
            let tmpbytes := mload(0x40)
            let byteLen := 0x20
            for {
                let tindex := 0x00
                let bindex := sub(byteLen, 0x01)
                let bvalue := mload(add(add(buff, 0x20), offset))
            } lt(tindex, byteLen) {
                tindex := add(tindex, 0x01)
                bindex := sub(bindex, 0x01)
            }{
                mstore8(add(tmpbytes, tindex), byte(bindex, bvalue))
            }
            mstore(0x40, add(tmpbytes, byteLen))
            v := mload(tmpbytes)
        }
        require(v <= 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, "Value exceeds the range");
        return (v, offset + 32);
    }
    /* @notice              Read next variable bytes starting from offset,
                            the decoding rule coming from multi-chain
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the bytes value
    *  @return              The read variable bytes array value and updated offset
    */
    function NextVarBytes(bytes memory buff, uint256 offset) internal pure returns(bytes memory, uint256) {
        uint len;
        (len, offset) = NextVarUint(buff, offset);
        require(offset + len <= buff.length && offset < offset + len, "NextVarBytes, offset exceeds maximum");
        bytes memory tempBytes;
        assembly{
            switch iszero(len)
            case 0 {
                // Get a location of some free memory and store it in tempBytes as
                // Solidity does for memory variables.
                tempBytes := mload(0x40)

                // The first word of the slice result is potentially a partial
                // word read from the original array. To read it, we calculate
                // the length of that partial word and start copying that many
                // bytes into the array. The first word we copy will start with
                // data we don't care about, but the last `lengthmod` bytes will
                // land at the beginning of the contents of the new array. When
                // we're done copying, we overwrite the full first word with
                // the actual length of the slice.
                let lengthmod := and(len, 31)

                // The multiplication in the next line is necessary
                // because when slicing multiples of 32 bytes (lengthmod == 0)
                // the following copy loop was copying the origin's length
                // and then ending prematurely not copying everything it should.
                let mc := add(add(tempBytes, lengthmod), mul(0x20, iszero(lengthmod)))
                let end := add(mc, len)

                for {
                    // The multiplication in the next line has the same exact purpose
                    // as the one above.
                    let cc := add(add(add(buff, lengthmod), mul(0x20, iszero(lengthmod))), offset)
                } lt(mc, end) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    mstore(mc, mload(cc))
                }

                mstore(tempBytes, len)

                //update free-memory pointer
                //allocating the array padded to 32 bytes like the compiler does now
                mstore(0x40, and(add(mc, 31), not(31)))
            }
            //if we want a zero-length slice let's just return a zero-length array
            default {
                tempBytes := mload(0x40)

                mstore(0x40, add(tempBytes, 0x20))
            }
        }

        return (tempBytes, offset + len);
    }
    /* @notice              Read next 32 bytes starting from offset,
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the bytes value
    *  @return              The read bytes32 value and updated offset
    */
    function NextHash(bytes memory buff, uint256 offset) internal pure returns (bytes32 , uint256) {
        require(offset + 32 <= buff.length && offset < offset + 32, "NextHash, offset exceeds maximum");
        bytes32 v;
        assembly {
            v := mload(add(buff, add(offset, 0x20)))
        }
        return (v, offset + 32);
    }

    /* @notice              Read next 20 bytes starting from offset,
    *  @param buff          Source bytes array
    *  @param offset        The position from where we read the bytes value
    *  @return              The read bytes20 value and updated offset
    */
    function NextBytes20(bytes memory buff, uint256 offset) internal pure returns (bytes20 , uint256) {
        require(offset + 20 <= buff.length && offset < offset + 20, "NextBytes20, offset exceeds maximum");
        bytes20 v;
        assembly {
            v := mload(add(buff, add(offset, 0x20)))
        }
        return (v, offset + 20);
    }
    
    function NextVarUint(bytes memory buff, uint256 offset) internal pure returns(uint, uint256) {
        byte v;
        (v, offset) = NextByte(buff, offset);

        uint value;
        if (v == 0xFD) {
            // return NextUint16(buff, offset);
            (value, offset) = NextUint16(buff, offset);
            require(value >= 0xFD && value <= 0xFFFF, "NextUint16, value outside range");
            return (value, offset);
        } else if (v == 0xFE) {
            // return NextUint32(buff, offset);
            (value, offset) = NextUint32(buff, offset);
            require(value > 0xFFFF && value <= 0xFFFFFFFF, "NextVarUint, value outside range");
            return (value, offset);
        } else if (v == 0xFF) {
            // return NextUint64(buff, offset);
            (value, offset) = NextUint64(buff, offset);
            require(value > 0xFFFFFFFF, "NextVarUint, value outside range");
            return (value, offset);
        } else{
            // return (uint8(v), offset);
            value = uint8(v);
            require(value < 0xFD, "NextVarUint, value outside range");
            return (value, offset);
        }
    }
}
// File: contracts/contracts/libs/ownership/Ownable.sol



pragma solidity ^0.5.0;

import "../GSN/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public  onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: contracts/contracts/libs/math/SafeMath.sol



pragma solidity ^0.5.0;

/**
 * @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.
     *
     * _Available since v2.4.0._
     */
    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.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        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.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: contracts/contracts/libs/token/ERC20/IERC20.sol



pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
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/contracts/libs/GSN/Context.sol



pragma solidity ^0.5.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 * Refer from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/GSN/Context.sol
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}