pragma solidity ^0.5.16;

// Inheritance
import "./interfaces/IERC20.sol";
import "./ExternStateToken.sol";
import "./MixinResolver.sol";
import "./interfaces/ISynthetix.sol";

// Internal references
import "./interfaces/ISynth.sol";
import "./TokenState.sol";
import "./interfaces/ISystemStatus.sol";
import "./interfaces/IExchanger.sol";
import "./interfaces/IIssuer.sol";
import "./interfaces/IRewardsDistribution.sol";
import "./interfaces/ILiquidator.sol";
import "./interfaces/ILiquidatorRewards.sol";
import "./interfaces/IVirtualSynth.sol";

contract BaseSynthetix is IERC20, ExternStateToken, MixinResolver, ISynthetix {
    // ========== STATE VARIABLES ==========

    // Available Synths which can be used with the system
    string public constant TOKEN_NAME = "Synthetix Network Token";
    string public constant TOKEN_SYMBOL = "SNX";
    uint8 public constant DECIMALS = 18;
    bytes32 public constant sUSD = "sUSD";

    // ========== ADDRESS RESOLVER CONFIGURATION ==========
    bytes32 private constant CONTRACT_SYSTEMSTATUS = "SystemStatus";
    bytes32 private constant CONTRACT_EXCHANGER = "Exchanger";
    bytes32 private constant CONTRACT_ISSUER = "Issuer";
    bytes32 private constant CONTRACT_REWARDSDISTRIBUTION = "RewardsDistribution";
    bytes32 private constant CONTRACT_LIQUIDATORREWARDS = "LiquidatorRewards";
    bytes32 private constant CONTRACT_LIQUIDATOR = "Liquidator";

    // ========== CONSTRUCTOR ==========

    constructor(
        address payable _proxy,
        TokenState _tokenState,
        address _owner,
        uint _totalSupply,
        address _resolver
    )
        public
        ExternStateToken(_proxy, _tokenState, TOKEN_NAME, TOKEN_SYMBOL, _totalSupply, DECIMALS, _owner)
        MixinResolver(_resolver)
    {}

    // ========== VIEWS ==========

    // Note: use public visibility so that it can be invoked in a subclass
    function resolverAddressesRequired() public view returns (bytes32[] memory addresses) {
        addresses = new bytes32[](6);
        addresses[0] = CONTRACT_SYSTEMSTATUS;
        addresses[1] = CONTRACT_EXCHANGER;
        addresses[2] = CONTRACT_ISSUER;
        addresses[3] = CONTRACT_REWARDSDISTRIBUTION;
        addresses[4] = CONTRACT_LIQUIDATORREWARDS;
        addresses[5] = CONTRACT_LIQUIDATOR;
    }

    function systemStatus() internal view returns (ISystemStatus) {
        return ISystemStatus(requireAndGetAddress(CONTRACT_SYSTEMSTATUS));
    }

    function exchanger() internal view returns (IExchanger) {
        return IExchanger(requireAndGetAddress(CONTRACT_EXCHANGER));
    }

    function issuer() internal view returns (IIssuer) {
        return IIssuer(requireAndGetAddress(CONTRACT_ISSUER));
    }

    function rewardsDistribution() internal view returns (IRewardsDistribution) {
        return IRewardsDistribution(requireAndGetAddress(CONTRACT_REWARDSDISTRIBUTION));
    }

    function liquidatorRewards() internal view returns (ILiquidatorRewards) {
        return ILiquidatorRewards(requireAndGetAddress(CONTRACT_LIQUIDATORREWARDS));
    }

    function liquidator() internal view returns (ILiquidator) {
        return ILiquidator(requireAndGetAddress(CONTRACT_LIQUIDATOR));
    }

    function debtBalanceOf(address account, bytes32 currencyKey) external view returns (uint) {
        return issuer().debtBalanceOf(account, currencyKey);
    }

    function totalIssuedSynths(bytes32 currencyKey) external view returns (uint) {
        return issuer().totalIssuedSynths(currencyKey, false);
    }

    function totalIssuedSynthsExcludeOtherCollateral(bytes32 currencyKey) external view returns (uint) {
        return issuer().totalIssuedSynths(currencyKey, true);
    }

    function availableCurrencyKeys() external view returns (bytes32[] memory) {
        return issuer().availableCurrencyKeys();
    }

    function availableSynthCount() external view returns (uint) {
        return issuer().availableSynthCount();
    }

    function availableSynths(uint index) external view returns (ISynth) {
        return issuer().availableSynths(index);
    }

    function synths(bytes32 currencyKey) external view returns (ISynth) {
        return issuer().synths(currencyKey);
    }

    function synthsByAddress(address synthAddress) external view returns (bytes32) {
        return issuer().synthsByAddress(synthAddress);
    }

    function isWaitingPeriod(bytes32 currencyKey) external view returns (bool) {
        return exchanger().maxSecsLeftInWaitingPeriod(messageSender, currencyKey) > 0;
    }

    function anySynthOrSNXRateIsInvalid() external view returns (bool anyRateInvalid) {
        return issuer().anySynthOrSNXRateIsInvalid();
    }

    function maxIssuableSynths(address account) external view returns (uint maxIssuable) {
        return issuer().maxIssuableSynths(account);
    }

    function remainingIssuableSynths(address account)
        external
        view
        returns (
            uint maxIssuable,
            uint alreadyIssued,
            uint totalSystemDebt
        )
    {
        return issuer().remainingIssuableSynths(account);
    }

    function collateralisationRatio(address _issuer) external view returns (uint) {
        return issuer().collateralisationRatio(_issuer);
    }

    function collateral(address account) external view returns (uint) {
        return issuer().collateral(account);
    }

    function transferableSynthetix(address account) external view returns (uint transferable) {
        (transferable, ) = issuer().transferableSynthetixAndAnyRateIsInvalid(account, tokenState.balanceOf(account));
    }

    function _canTransfer(address account, uint value) internal view returns (bool) {
        if (issuer().debtBalanceOf(account, sUSD) > 0) {
            (uint transferable, bool anyRateIsInvalid) =
                issuer().transferableSynthetixAndAnyRateIsInvalid(account, tokenState.balanceOf(account));
            require(value <= transferable, "Cannot transfer staked or escrowed SNX");
            require(!anyRateIsInvalid, "A synth or SNX rate is invalid");
        }

        return true;
    }

    // ========== MUTATIVE FUNCTIONS ==========

    function exchange(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    ) external exchangeActive(sourceCurrencyKey, destinationCurrencyKey) optionalProxy returns (uint amountReceived) {
        (amountReceived, ) = exchanger().exchange(
            messageSender,
            messageSender,
            sourceCurrencyKey,
            sourceAmount,
            destinationCurrencyKey,
            messageSender,
            false,
            messageSender,
            bytes32(0)
        );
    }

    function exchangeOnBehalf(
        address exchangeForAddress,
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    ) external exchangeActive(sourceCurrencyKey, destinationCurrencyKey) optionalProxy returns (uint amountReceived) {
        (amountReceived, ) = exchanger().exchange(
            exchangeForAddress,
            messageSender,
            sourceCurrencyKey,
            sourceAmount,
            destinationCurrencyKey,
            exchangeForAddress,
            false,
            exchangeForAddress,
            bytes32(0)
        );
    }

    function settle(bytes32 currencyKey)
        external
        optionalProxy
        returns (
            uint reclaimed,
            uint refunded,
            uint numEntriesSettled
        )
    {
        return exchanger().settle(messageSender, currencyKey);
    }

    function exchangeWithTracking(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey,
        address rewardAddress,
        bytes32 trackingCode
    ) external exchangeActive(sourceCurrencyKey, destinationCurrencyKey) optionalProxy returns (uint amountReceived) {
        (amountReceived, ) = exchanger().exchange(
            messageSender,
            messageSender,
            sourceCurrencyKey,
            sourceAmount,
            destinationCurrencyKey,
            messageSender,
            false,
            rewardAddress,
            trackingCode
        );
    }

    function exchangeOnBehalfWithTracking(
        address exchangeForAddress,
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey,
        address rewardAddress,
        bytes32 trackingCode
    ) external exchangeActive(sourceCurrencyKey, destinationCurrencyKey) optionalProxy returns (uint amountReceived) {
        (amountReceived, ) = exchanger().exchange(
            exchangeForAddress,
            messageSender,
            sourceCurrencyKey,
            sourceAmount,
            destinationCurrencyKey,
            exchangeForAddress,
            false,
            rewardAddress,
            trackingCode
        );
    }

    function transfer(address to, uint value) external onlyProxyOrInternal systemActive returns (bool) {
        // Ensure they're not trying to exceed their locked amount -- only if they have debt.
        _canTransfer(messageSender, value);

        // Perform the transfer: if there is a problem an exception will be thrown in this call.
        _transferByProxy(messageSender, to, value);

        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint value
    ) external onlyProxyOrInternal systemActive returns (bool) {
        // Ensure they're not trying to exceed their locked amount -- only if they have debt.
        _canTransfer(from, value);

        // Perform the transfer: if there is a problem,
        // an exception will be thrown in this call.
        return _transferFromByProxy(messageSender, from, to, value);
    }

    function issueSynths(uint amount) external issuanceActive optionalProxy {
        return issuer().issueSynths(messageSender, amount);
    }

    function issueSynthsOnBehalf(address issueForAddress, uint amount) external issuanceActive optionalProxy {
        return issuer().issueSynthsOnBehalf(issueForAddress, messageSender, amount);
    }

    function issueMaxSynths() external issuanceActive optionalProxy {
        return issuer().issueMaxSynths(messageSender);
    }

    function issueMaxSynthsOnBehalf(address issueForAddress) external issuanceActive optionalProxy {
        return issuer().issueMaxSynthsOnBehalf(issueForAddress, messageSender);
    }

    function burnSynths(uint amount) external issuanceActive optionalProxy {
        return issuer().burnSynths(messageSender, amount);
    }

    function burnSynthsOnBehalf(address burnForAddress, uint amount) external issuanceActive optionalProxy {
        return issuer().burnSynthsOnBehalf(burnForAddress, messageSender, amount);
    }

    function burnSynthsToTarget() external issuanceActive optionalProxy {
        return issuer().burnSynthsToTarget(messageSender);
    }

    function burnSynthsToTargetOnBehalf(address burnForAddress) external issuanceActive optionalProxy {
        return issuer().burnSynthsToTargetOnBehalf(burnForAddress, messageSender);
    }

    /// @notice Force liquidate a delinquent account and distribute the redeemed SNX rewards amongst the appropriate recipients.
    /// @dev The SNX transfers will revert if the amount to send is more than balanceOf account (i.e. due to escrowed balance).
    function liquidateDelinquentAccount(address account) external systemActive optionalProxy returns (bool) {
        (uint totalRedeemed, uint amountLiquidated) = issuer().liquidateAccount(account, false);

        emitAccountLiquidated(account, totalRedeemed, amountLiquidated, messageSender);

        if (totalRedeemed > 0) {
            uint stakerRewards; // The amount of rewards to be sent to the LiquidatorRewards contract.
            uint flagReward = liquidator().flagReward();
            uint liquidateReward = liquidator().liquidateReward();
            // Check if the total amount of redeemed SNX is enough to payout the liquidation rewards.
            if (totalRedeemed > flagReward.add(liquidateReward)) {
                // Transfer the flagReward to the account who flagged this account for liquidation.
                address flagger = liquidator().getLiquidationCallerForAccount(account);
                bool flagRewardTransferSucceeded = _transferByProxy(account, flagger, flagReward);
                require(flagRewardTransferSucceeded, "Flag reward transfer did not succeed");

                // Transfer the liquidateReward to liquidator (the account who invoked this liquidation).
                bool liquidateRewardTransferSucceeded = _transferByProxy(account, messageSender, liquidateReward);
                require(liquidateRewardTransferSucceeded, "Liquidate reward transfer did not succeed");

                // The remaining SNX to be sent to the LiquidatorRewards contract.
                stakerRewards = totalRedeemed.sub(flagReward.add(liquidateReward));
            } else {
                /* If the total amount of redeemed SNX is greater than zero 
                but is less than the sum of the flag & liquidate rewards,
                then just send all of the SNX to the LiquidatorRewards contract. */
                stakerRewards = totalRedeemed;
            }

            bool liquidatorRewardTransferSucceeded = _transferByProxy(account, address(liquidatorRewards()), stakerRewards);
            require(liquidatorRewardTransferSucceeded, "Transfer to LiquidatorRewards failed");

            // Inform the LiquidatorRewards contract about the incoming SNX rewards.
            liquidatorRewards().notifyRewardAmount(stakerRewards);

            return true;
        } else {
            // In this unlikely case, the total redeemed SNX is not greater than zero so don't perform any transfers.
            return false;
        }
    }

    /// @notice Allows an account to self-liquidate anytime its c-ratio is below the target issuance ratio.
    function liquidateSelf() external systemActive optionalProxy returns (bool) {
        // Self liquidate the account (`isSelfLiquidation` flag must be set to `true`).
        (uint totalRedeemed, uint amountLiquidated) = issuer().liquidateAccount(messageSender, true);

        emitAccountLiquidated(messageSender, totalRedeemed, amountLiquidated, messageSender);

        // Transfer the redeemed SNX to the LiquidatorRewards contract.
        // Reverts if amount to redeem is more than balanceOf account (i.e. due to escrowed balance).
        bool success = _transferByProxy(messageSender, address(liquidatorRewards()), totalRedeemed);
        require(success, "Transfer to LiquidatorRewards failed");

        // Inform the LiquidatorRewards contract about the incoming SNX rewards.
        liquidatorRewards().notifyRewardAmount(totalRedeemed);

        return success;
    }

    /**
     * @notice Once off function for SIP-239 to recover unallocated SNX rewards
     * due to an initialization issue in the LiquidatorRewards contract deployed in SIP-148.
     * @param amount The amount of SNX to be recovered and distributed to the rightful owners
     */
    bool public restituted = false;

    function initializeLiquidatorRewardsRestitution(uint amount) external onlyOwner {
        if (!restituted) {
            restituted = true;
            bool success = _transferByProxy(address(liquidatorRewards()), owner, amount);
            require(success, "restitution transfer failed");
        }
    }

    function exchangeWithTrackingForInitiator(
        bytes32,
        uint,
        bytes32,
        address,
        bytes32
    ) external returns (uint) {
        _notImplemented();
    }

    function exchangeWithVirtual(
        bytes32,
        uint,
        bytes32,
        bytes32
    ) external returns (uint, IVirtualSynth) {
        _notImplemented();
    }

    function exchangeAtomically(
        bytes32,
        uint,
        bytes32,
        bytes32,
        uint
    ) external returns (uint) {
        _notImplemented();
    }

    function mint() external returns (bool) {
        _notImplemented();
    }

    function mintSecondary(address, uint) external {
        _notImplemented();
    }

    function mintSecondaryRewards(uint) external {
        _notImplemented();
    }

    function burnSecondary(address, uint) external {
        _notImplemented();
    }

    function _notImplemented() internal pure {
        revert("Cannot be run on this layer");
    }

    // ========== MODIFIERS ==========

    modifier systemActive() {
        _systemActive();
        _;
    }

    function _systemActive() private view {
        systemStatus().requireSystemActive();
    }

    modifier issuanceActive() {
        _issuanceActive();
        _;
    }

    function _issuanceActive() private view {
        systemStatus().requireIssuanceActive();
    }

    modifier exchangeActive(bytes32 src, bytes32 dest) {
        _exchangeActive(src, dest);
        _;
    }

    function _exchangeActive(bytes32 src, bytes32 dest) private view {
        systemStatus().requireExchangeBetweenSynthsAllowed(src, dest);
    }

    modifier onlyExchanger() {
        _onlyExchanger();
        _;
    }

    function _onlyExchanger() private view {
        require(msg.sender == address(exchanger()), "Only Exchanger can invoke this");
    }

    modifier onlyProxyOrInternal {
        _onlyProxyOrInternal();
        _;
    }

    function _onlyProxyOrInternal() internal {
        if (msg.sender == address(proxy)) {
            // allow proxy through, messageSender should be already set correctly
            return;
        } else if (_isInternalTransferCaller(msg.sender)) {
            // optionalProxy behaviour only for the internal legacy contracts
            messageSender = msg.sender;
        } else {
            revert("Only the proxy can call");
        }
    }

    /// some legacy internal contracts use transfer methods directly on implementation
    /// which isn't supported due to SIP-238 for other callers
    function _isInternalTransferCaller(address caller) internal view returns (bool) {
        // These entries are not required or cached in order to allow them to not exist (==address(0))
        // e.g. due to not being available on L2 or at some future point in time.
        return
            // ordered to reduce gas for more frequent calls, bridge first, vesting after, legacy last
            caller == resolver.getAddress("SynthetixBridgeToOptimism") ||
            caller == resolver.getAddress("RewardEscrowV2") ||
            // legacy contracts
            caller == resolver.getAddress("RewardEscrow") ||
            caller == resolver.getAddress("SynthetixEscrow") ||
            caller == resolver.getAddress("TradingRewards") ||
            caller == resolver.getAddress("Depot");
    }

    // ========== EVENTS ==========
    event AccountLiquidated(address indexed account, uint snxRedeemed, uint amountLiquidated, address liquidator);
    bytes32 internal constant ACCOUNTLIQUIDATED_SIG = keccak256("AccountLiquidated(address,uint256,uint256,address)");

    function emitAccountLiquidated(
        address account,
        uint256 snxRedeemed,
        uint256 amountLiquidated,
        address liquidator
    ) internal {
        proxy._emit(
            abi.encode(snxRedeemed, amountLiquidated, liquidator),
            2,
            ACCOUNTLIQUIDATED_SIG,
            addressToBytes32(account),
            0,
            0
        );
    }

    event SynthExchange(
        address indexed account,
        bytes32 fromCurrencyKey,
        uint256 fromAmount,
        bytes32 toCurrencyKey,
        uint256 toAmount,
        address toAddress
    );
    bytes32 internal constant SYNTH_EXCHANGE_SIG =
        keccak256("SynthExchange(address,bytes32,uint256,bytes32,uint256,address)");

    function emitSynthExchange(
        address account,
        bytes32 fromCurrencyKey,
        uint256 fromAmount,
        bytes32 toCurrencyKey,
        uint256 toAmount,
        address toAddress
    ) external onlyExchanger {
        proxy._emit(
            abi.encode(fromCurrencyKey, fromAmount, toCurrencyKey, toAmount, toAddress),
            2,
            SYNTH_EXCHANGE_SIG,
            addressToBytes32(account),
            0,
            0
        );
    }

    event ExchangeTracking(bytes32 indexed trackingCode, bytes32 toCurrencyKey, uint256 toAmount, uint256 fee);
    bytes32 internal constant EXCHANGE_TRACKING_SIG = keccak256("ExchangeTracking(bytes32,bytes32,uint256,uint256)");

    function emitExchangeTracking(
        bytes32 trackingCode,
        bytes32 toCurrencyKey,
        uint256 toAmount,
        uint256 fee
    ) external onlyExchanger {
        proxy._emit(abi.encode(toCurrencyKey, toAmount, fee), 2, EXCHANGE_TRACKING_SIG, trackingCode, 0, 0);
    }

    event ExchangeReclaim(address indexed account, bytes32 currencyKey, uint amount);
    bytes32 internal constant EXCHANGERECLAIM_SIG = keccak256("ExchangeReclaim(address,bytes32,uint256)");

    function emitExchangeReclaim(
        address account,
        bytes32 currencyKey,
        uint256 amount
    ) external onlyExchanger {
        proxy._emit(abi.encode(currencyKey, amount), 2, EXCHANGERECLAIM_SIG, addressToBytes32(account), 0, 0);
    }

    event ExchangeRebate(address indexed account, bytes32 currencyKey, uint amount);
    bytes32 internal constant EXCHANGEREBATE_SIG = keccak256("ExchangeRebate(address,bytes32,uint256)");

    function emitExchangeRebate(
        address account,
        bytes32 currencyKey,
        uint256 amount
    ) external onlyExchanger {
        proxy._emit(abi.encode(currencyKey, amount), 2, EXCHANGEREBATE_SIG, addressToBytes32(account), 0, 0);
    }
}