pragma solidity ^0.4.24;

// File: contracts/token/interfaces/IERC20Token.sol

/*
    ERC20 Standard Token interface
*/
contract IERC20Token {
    // these functions aren't abstract since the compiler emits automatically generated getter functions as external
    function name() public view returns (string) {}
    function symbol() public view returns (string) {}
    function decimals() public view returns (uint8) {}
    function totalSupply() public view returns (uint256) {}
    function balanceOf(address _owner) public view returns (uint256) { _owner; }
    function allowance(address _owner, address _spender) public view returns (uint256) { _owner; _spender; }

    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
}

// File: contracts/utility/interfaces/IOwned.sol

/*
    Owned contract interface
*/
contract IOwned {
    // this function isn't abstract since the compiler emits automatically generated getter functions as external
    function owner() public view returns (address) {}

    function transferOwnership(address _newOwner) public;
    function acceptOwnership() public;
}

// File: contracts/token/interfaces/ISmartToken.sol

/*
    Smart Token interface
*/
contract ISmartToken is IOwned, IERC20Token {
    function disableTransfers(bool _disable) public;
    function issue(address _to, uint256 _amount) public;
    function destroy(address _from, uint256 _amount) public;
}

// File: contracts/utility/interfaces/IWhitelist.sol

/*
    Whitelist interface
*/
contract IWhitelist {
    function isWhitelisted(address _address) public view returns (bool);
}

// File: contracts/converter/interfaces/IBancorConverter.sol

/*
    Bancor Converter interface
*/
contract IBancorConverter {
    function getReturn(IERC20Token _fromToken, IERC20Token _toToken, uint256 _amount) public view returns (uint256, uint256);
    function convert(IERC20Token _fromToken, IERC20Token _toToken, uint256 _amount, uint256 _minReturn) public returns (uint256);
    function conversionWhitelist() public view returns (IWhitelist) {}
    function conversionFee() public view returns (uint32) {}
    function connectors(address _address) public view returns (uint256, uint32, bool, bool, bool) { _address; }
    function getConnectorBalance(IERC20Token _connectorToken) public view returns (uint256);
    function claimTokens(address _from, uint256 _amount) public;
    // deprecated, backward compatibility
    function change(IERC20Token _fromToken, IERC20Token _toToken, uint256 _amount, uint256 _minReturn) public returns (uint256);
}

// File: contracts/ContractIds.sol

/**
    Id definitions for bancor contracts

    Can be used in conjunction with the contract registry to get contract addresses
*/
contract ContractIds {
    // generic
    bytes32 public constant CONTRACT_FEATURES = "ContractFeatures";
    bytes32 public constant CONTRACT_REGISTRY = "ContractRegistry";

    // bancor logic
    bytes32 public constant BANCOR_NETWORK = "BancorNetwork";
    bytes32 public constant BANCOR_FORMULA = "BancorFormula";
    bytes32 public constant BANCOR_GAS_PRICE_LIMIT = "BancorGasPriceLimit";
    bytes32 public constant BANCOR_CONVERTER_UPGRADER = "BancorConverterUpgrader";
    bytes32 public constant BANCOR_CONVERTER_FACTORY = "BancorConverterFactory";

    // Ids of BNT converter and BNT token
    bytes32 public constant BNT_TOKEN = "BNTToken";
    bytes32 public constant BNT_CONVERTER = "BNTConverter";

    // Id of BancorX contract
    bytes32 public constant BANCOR_X = "BancorX";
}

// File: contracts/utility/interfaces/IContractRegistry.sol

/*
    Contract Registry interface
*/
contract IContractRegistry {
    function addressOf(bytes32 _contractName) public view returns (address);

    // deprecated, backward compatibility
    function getAddress(bytes32 _contractName) public view returns (address);
}

// File: contracts/utility/Owned.sol

/*
    Provides support and utilities for contract ownership
*/
contract Owned is IOwned {
    address public owner;
    address public newOwner;

    event OwnerUpdate(address indexed _prevOwner, address indexed _newOwner);

    /**
        @dev constructor
    */
    constructor() public {
        owner = msg.sender;
    }

    // allows execution by the owner only
    modifier ownerOnly {
        require(msg.sender == owner);
        _;
    }

    /**
        @dev allows transferring the contract ownership
        the new owner still needs to accept the transfer
        can only be called by the contract owner

        @param _newOwner    new contract owner
    */
    function transferOwnership(address _newOwner) public ownerOnly {
        require(_newOwner != owner);
        newOwner = _newOwner;
    }

    /**
        @dev used by a new owner to accept an ownership transfer
    */
    function acceptOwnership() public {
        require(msg.sender == newOwner);
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

// File: contracts/utility/Utils.sol

/*
    Utilities & Common Modifiers
*/
contract Utils {
    /**
        constructor
    */
    constructor() public {
    }

    // verifies that an amount is greater than zero
    modifier greaterThanZero(uint256 _amount) {
        require(_amount > 0);
        _;
    }

    // validates an address - currently only checks that it isn't null
    modifier validAddress(address _address) {
        require(_address != address(0));
        _;
    }

    // verifies that the address is different than this contract address
    modifier notThis(address _address) {
        require(_address != address(this));
        _;
    }

    // Overflow protected math functions

    /**
        @dev returns the sum of _x and _y, asserts if the calculation overflows

        @param _x   value 1
        @param _y   value 2

        @return sum
    */
    function safeAdd(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x + _y;
        assert(z >= _x);
        return z;
    }

    /**
        @dev returns the difference of _x minus _y, asserts if the subtraction results in a negative number

        @param _x   minuend
        @param _y   subtrahend

        @return difference
    */
    function safeSub(uint256 _x, uint256 _y) internal pure returns (uint256) {
        assert(_x >= _y);
        return _x - _y;
    }

    /**
        @dev returns the product of multiplying _x by _y, asserts if the calculation overflows

        @param _x   factor 1
        @param _y   factor 2

        @return product
    */
    function safeMul(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x * _y;
        assert(_x == 0 || z / _x == _y);
        return z;
    }
}

// File: contracts/utility/interfaces/ITokenHolder.sol

/*
    Token Holder interface
*/
contract ITokenHolder is IOwned {
    function withdrawTokens(IERC20Token _token, address _to, uint256 _amount) public;
}

// File: contracts/utility/TokenHolder.sol

/*
    We consider every contract to be a 'token holder' since it's currently not possible
    for a contract to deny receiving tokens.

    The TokenHolder's contract sole purpose is to provide a safety mechanism that allows
    the owner to send tokens that were sent to the contract by mistake back to their sender.
*/
contract TokenHolder is ITokenHolder, Owned, Utils {
    /**
        @dev constructor
    */
    constructor() public {
    }

    /**
        @dev withdraws tokens held by the contract and sends them to an account
        can only be called by the owner

        @param _token   ERC20 token contract address
        @param _to      account to receive the new amount
        @param _amount  amount to withdraw
    */
    function withdrawTokens(IERC20Token _token, address _to, uint256 _amount)
        public
        ownerOnly
        validAddress(_token)
        validAddress(_to)
        notThis(_to)
    {
        assert(_token.transfer(_to, _amount));
    }
}

// File: contracts/utility/SafeMath.sol

/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, reverts on 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-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b);

    return c;
  }

  /**
  * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b > 0); // Solidity only automatically asserts when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
  * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    uint256 c = a - b;

    return c;
  }

  /**
  * @dev Adds two numbers, reverts on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);

    return c;
  }

  /**
  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
  * reverts when dividing by zero.
  */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
  }
}

// File: contracts/BancorX.sol

contract BancorX is Owned, TokenHolder, ContractIds {
    using SafeMath for uint256;

    // represents a transaction on another blockchain where BNT was destroyed/locked
    struct Transaction {
        uint256 amount;
        bytes32 fromBlockchain;
        address to;
        uint8 numOfReports;
        bool completed;
    }

    uint256 public maxLockLimit;                   // the maximum amount of BNT that can be locked in one transaction
    uint256 public maxReleaseLimit;                // the maximum amount of BNT that can be released in one transaction
    uint256 public minLimit;                       // the minimum amount of BNT that can be transferred in one transaction
    uint256 public prevLockLimit;                  // the lock limit *after* the last transaction
    uint256 public prevReleaseLimit;               // the release limit *after* the last transaction
    uint256 public limitIncPerBlock;               // how much the limit increases per block
    uint256 public prevLockBlockNumber;            // the block number of the last lock transaction
    uint256 public prevReleaseBlockNumber;         // the block number of the last release transaction
    uint256 public minRequiredReports;             // minimum number of required reports to release tokens
    
    IContractRegistry public registry;             // contract registry
    IContractRegistry public prevRegistry;         // address of previous registry as security mechanism
    IBancorConverter public bntConverter;          // BNT converter
    ISmartToken public bntToken;                   // BNT token

    bool public xTransfersEnabled = true;          // true if x transfers are enabled, false if not
    bool public reportingEnabled = true;           // true if reporting is enabled, false if not
    bool public allowRegistryUpdate = true;        // allows the owner to prevent/allow the registry to be updated

    // txId -> Transaction
    mapping (uint256 => Transaction) public transactions;

    // txId -> reporter -> true if reporter already reported txId
    mapping (uint256 => mapping (address => bool)) public reportedTxs;

    // address -> true if address is reporter
    mapping (address => bool) public reporters;

    // triggered when BNT is locked in smart contract
    event TokensLock(
        address indexed _from,
        uint256 _amount
    );

    // triggered when BNT is released by the smart contract
    event TokensRelease(
        address indexed _to,
        uint256 _amount
    );

    // triggered when xTransfer is successfully called
    event XTransfer(
        address indexed _from,
        bytes32 _toBlockchain,
        bytes32 indexed _to,
        uint256 _amount
    );

    // triggered when report is successfully submitted
    event TxReport(
        address indexed _reporter,
        bytes32 _fromBlockchain,
        uint256 _txId,
        address _to,
        uint256 _amount
    );

    /**
        @dev constructor

        @param _maxLockLimit          maximum amount of BNT that can be locked in one transaction
        @param _maxReleaseLimit       maximum amount of BNT that can be released in one transaction
        @param _minLimit              minimum amount of BNT that can be transferred in one transaction
        @param _limitIncPerBlock      how much the limit increases per block
        @param _minRequiredReports    minimum number of reporters to report transaction before tokens can be released
        @param _registry              address of contract registry
     */
    constructor(
        uint256 _maxLockLimit,
        uint256 _maxReleaseLimit,
        uint256 _minLimit,
        uint256 _limitIncPerBlock,
        uint256 _minRequiredReports,
        address _registry
    )
        public
    {
        // the maximum limits, minimum limit, and limit increase per block
        maxLockLimit = _maxLockLimit;
        maxReleaseLimit = _maxReleaseLimit;
        minLimit = _minLimit;
        limitIncPerBlock = _limitIncPerBlock;
        minRequiredReports = _minRequiredReports;

        // previous limit is _maxLimit, and previous block number is current block number
        prevLockLimit = _maxLockLimit;
        prevReleaseLimit = _maxReleaseLimit;
        prevLockBlockNumber = block.number;
        prevReleaseBlockNumber = block.number;

        registry = IContractRegistry(_registry);
        prevRegistry = IContractRegistry(_registry);
        bntToken = ISmartToken(registry.addressOf(ContractIds.BNT_TOKEN));
        bntConverter = IBancorConverter(registry.addressOf(ContractIds.BNT_CONVERTER));
    }

    // validates that the caller is a reporter
    modifier isReporter {
        require(reporters[msg.sender]);
        _;
    }

    // allows execution only when x transfers are enabled
    modifier whenXTransfersEnabled {
        require(xTransfersEnabled);
        _;
    }

    // allows execution only when reporting is enabled
    modifier whenReportingEnabled {
        require(reportingEnabled);
        _;
    }

    /**
        @dev setter

        @param _maxLockLimit    new maxLockLimit
     */
    function setMaxLockLimit(uint256 _maxLockLimit) public ownerOnly {
        maxLockLimit = _maxLockLimit;
    }
    
    /**
        @dev setter

        @param _maxReleaseLimit    new maxReleaseLimit
     */
    function setMaxReleaseLimit(uint256 _maxReleaseLimit) public ownerOnly {
        maxReleaseLimit = _maxReleaseLimit;
    }
    
    /**
        @dev setter

        @param _minLimit    new minLimit
     */
    function setMinLimit(uint256 _minLimit) public ownerOnly {
        minLimit = _minLimit;
    }

    /**
        @dev setter

        @param _limitIncPerBlock    new limitIncPerBlock
     */
    function setLimitIncPerBlock(uint256 _limitIncPerBlock) public ownerOnly {
        limitIncPerBlock = _limitIncPerBlock;
    }

    /**
        @dev setter

        @param _minRequiredReports    new minRequiredReports
     */
    function setMinRequiredReports(uint256 _minRequiredReports) public ownerOnly {
        minRequiredReports = _minRequiredReports;
    }

    /**
        @dev allows the owner to set/remove reporters

        @param _reporter    reporter whos status is to be set
        @param _active      true if the reporter is approved, false otherwise
     */
    function setReporter(address _reporter, bool _active) public ownerOnly {
        reporters[_reporter] = _active;
    }

    /**
        @dev allows the owner enable/disable the xTransfer method

        @param _enable     true to enable, false to disable
     */
    function enableXTransfers(bool _enable) public ownerOnly {
        xTransfersEnabled = _enable;
    }

    /**
        @dev allows the owner enable/disable the reportTransaction method

        @param _enable     true to enable, false to disable
     */
    function enableReporting(bool _enable) public ownerOnly {
        reportingEnabled = _enable;
    }

    /**
        @dev disables the registry update functionality
        this is a safety mechanism in case of a emergency
        can only be called by the manager or owner

        @param _disable    true to disable registry updates, false to re-enable them
    */
    function disableRegistryUpdate(bool _disable) public ownerOnly {
        allowRegistryUpdate = !_disable;
    }

    /**
        @dev allows the owner to set the BNT converters address to wherever the
        contract registry currently points to
     */
    function setBNTConverterAddress() public ownerOnly {
        bntConverter = IBancorConverter(registry.addressOf(ContractIds.BNT_CONVERTER));
    }

    /**
        @dev sets the contract registry to whichever address the current registry is pointing to
     */
    function updateRegistry() public {
        // require that upgrading is allowed or that the caller is the owner
        require(allowRegistryUpdate || msg.sender == owner);

        // get the address of whichever registry the current registry is pointing to
        address newRegistry = registry.addressOf(ContractIds.CONTRACT_REGISTRY);

        // if the new registry hasn't changed or is the zero address, revert
        require(newRegistry != address(registry) && newRegistry != address(0));

        // set the previous registry as current registry and current registry as newRegistry
        prevRegistry = registry;
        registry = IContractRegistry(newRegistry);
    }

    /**
        @dev security mechanism allowing the converter owner to revert to the previous registry,
        to be used in emergency scenario
    */
    function restoreRegistry() public ownerOnly {
        // set the registry as previous registry
        registry = prevRegistry;

        // after a previous registry is restored, only the owner can allow future updates
        allowRegistryUpdate = false;
    }


    /**
        @dev claims BNT from msg.sender to be converted to BNT on another blockchain

        @param _toBlockchain    blockchain BNT will be issued on
        @param _to              address to send the BNT to
        @param _amount          the amount to transfer
     */
    function xTransfer(bytes32 _toBlockchain, bytes32 _to, uint256 _amount) public whenXTransfersEnabled {
        // get the current lock limit
        uint256 currentLockLimit = getCurrentLockLimit();

        // require that; minLimit <= _amount <= currentLockLimit
        require(_amount >= minLimit && _amount <= currentLockLimit);
        
        lockTokens(_amount);

        // set the previous lock limit and block number
        prevLockLimit = currentLockLimit.sub(_amount);
        prevLockBlockNumber = block.number;

        emit XTransfer(msg.sender, _toBlockchain, _to, _amount);
    }

    /**
        @dev allows reporter to report transaction which occured on another blockchain

        @param _fromBlockchain  blockchain BNT was destroyed in
        @param _txId            transactionId of transaction thats being reported
        @param _to              address to receive BNT
        @param _amount          amount of BNT destroyed on another blockchain
     */
    function reportTx(
        bytes32 _fromBlockchain,
        uint256 _txId,
        address _to,
        uint256 _amount    
    )
        public
        isReporter
        whenReportingEnabled
    {
        // require that the transaction has not been reported yet by the reporter
        require(!reportedTxs[_txId][msg.sender]);

        // set reported as true
        reportedTxs[_txId][msg.sender] = true;

        Transaction storage txn = transactions[_txId];

        // If the caller is the first reporter, set the transaction details
        if (txn.numOfReports == 0) {
            txn.to = _to;
            txn.amount = _amount;
            txn.fromBlockchain = _fromBlockchain;
        } else {
            // otherwise, verify transaction details
            require(txn.to == _to && txn.amount == _amount && txn.fromBlockchain == _fromBlockchain);
        }
        
        // increment the number of reports
        txn.numOfReports++;

        emit TxReport(msg.sender, _fromBlockchain, _txId, _to, _amount);

        // if theres enough reports, try to release tokens
        if (txn.numOfReports >= minRequiredReports) {
            require(!transactions[_txId].completed);

            // set the transaction as completed
            transactions[_txId].completed = true;

            releaseTokens(_to, _amount);
        }
    }

    /**
        @dev method for calculating current lock limit

        @return the current maximum limit of BNT that can be locked
     */
    function getCurrentLockLimit() public view returns (uint256) {
        // prevLockLimit + ((currBlockNumber - prevLockBlockNumber) * limitIncPerBlock)
        uint256 currentLockLimit = prevLockLimit.add(((block.number).sub(prevLockBlockNumber)).mul(limitIncPerBlock));
        if (currentLockLimit > maxLockLimit)
            return maxLockLimit;
        return currentLockLimit;
    }
 
    /**
        @dev method for calculating current release limit

        @return the current maximum limit of BNT that can be released
     */
    function getCurrentReleaseLimit() public view returns (uint256) {
        // prevReleaseLimit + ((currBlockNumber - prevReleaseBlockNumber) * limitIncPerBlock)
        uint256 currentReleaseLimit = prevReleaseLimit.add(((block.number).sub(prevReleaseBlockNumber)).mul(limitIncPerBlock));
        if (currentReleaseLimit > maxReleaseLimit)
            return maxReleaseLimit;
        return currentReleaseLimit;
    }

    /**
        @dev claims and locks BNT from msg.sender to be converted to BNT on another blockchain

        @param _amount  the amount to lock
     */
    function lockTokens(uint256 _amount) private {
        // lock the BNT from msg.sender in this contract
        bntConverter.claimTokens(msg.sender, _amount);

        emit TokensLock(msg.sender, _amount);
    }

    /**
        @dev private method to release BNT the contract holds

        @param _to      the address to release BNT to
        @param _amount  the amount to release
     */
    function releaseTokens(address _to, uint256 _amount) private {
        // get the current release limit
        uint256 currentReleaseLimit = getCurrentReleaseLimit();

        require(_amount >= minLimit && _amount <= currentReleaseLimit);
        
        // update the previous release limit and block number
        prevReleaseLimit = currentReleaseLimit.sub(_amount);
        prevReleaseBlockNumber = block.number;

        // no need to require, reverts on failure
        bntToken.transfer(_to, _amount);

        emit TokensRelease(_to, _amount);
    }
}