pragma solidity ^0.5.16;

// Inheritance
import "./Owned.sol";
import "./MixinResolver.sol";
import "./MixinSystemSettings.sol";
import "./interfaces/IDebtCache.sol";

// Libraries
import "./SafeDecimalMath.sol";

// Internal references
import "./interfaces/IIssuer.sol";
import "./interfaces/IExchanger.sol";
import "./interfaces/IExchangeRates.sol";
import "./interfaces/ISystemStatus.sol";
import "./interfaces/IEtherCollateral.sol";
import "./interfaces/IEtherCollateralsUSD.sol";
import "./interfaces/IERC20.sol";
import "./interfaces/ICollateralManager.sol";


// https://docs.synthetix.io/contracts/source/contracts/debtcache
contract DebtCache is Owned, MixinSystemSettings, IDebtCache {
    using SafeMath for uint;
    using SafeDecimalMath for uint;

    uint internal _cachedDebt;
    mapping(bytes32 => uint) internal _cachedSynthDebt;
    uint internal _cacheTimestamp;
    bool internal _cacheInvalid = true;

    /* ========== ENCODED NAMES ========== */

    bytes32 internal constant sUSD = "sUSD";
    bytes32 internal constant sETH = "sETH";

    /* ========== ADDRESS RESOLVER CONFIGURATION ========== */

    bytes32 private constant CONTRACT_ISSUER = "Issuer";
    bytes32 private constant CONTRACT_EXCHANGER = "Exchanger";
    bytes32 private constant CONTRACT_EXRATES = "ExchangeRates";
    bytes32 private constant CONTRACT_SYSTEMSTATUS = "SystemStatus";
    bytes32 private constant CONTRACT_ETHERCOLLATERAL = "EtherCollateral";
    bytes32 private constant CONTRACT_ETHERCOLLATERAL_SUSD = "EtherCollateralsUSD";
    bytes32 private constant CONTRACT_COLLATERALMANAGER = "CollateralManager";

    constructor(address _owner, address _resolver) public Owned(_owner) MixinSystemSettings(_resolver) {}

    /* ========== VIEWS ========== */

    function resolverAddressesRequired() public view returns (bytes32[] memory addresses) {
        bytes32[] memory existingAddresses = MixinSystemSettings.resolverAddressesRequired();
        bytes32[] memory newAddresses = new bytes32[](7);
        newAddresses[0] = CONTRACT_ISSUER;
        newAddresses[1] = CONTRACT_EXCHANGER;
        newAddresses[2] = CONTRACT_EXRATES;
        newAddresses[3] = CONTRACT_SYSTEMSTATUS;
        newAddresses[4] = CONTRACT_ETHERCOLLATERAL;
        newAddresses[5] = CONTRACT_ETHERCOLLATERAL_SUSD;
        newAddresses[6] = CONTRACT_COLLATERALMANAGER;
        addresses = combineArrays(existingAddresses, newAddresses);
    }

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

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

    function exchangeRates() internal view returns (IExchangeRates) {
        return IExchangeRates(requireAndGetAddress(CONTRACT_EXRATES));
    }

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

    function etherCollateral() internal view returns (IEtherCollateral) {
        return IEtherCollateral(requireAndGetAddress(CONTRACT_ETHERCOLLATERAL));
    }

    function etherCollateralsUSD() internal view returns (IEtherCollateralsUSD) {
        return IEtherCollateralsUSD(requireAndGetAddress(CONTRACT_ETHERCOLLATERAL_SUSD));
    }

    function collateralManager() internal view returns (ICollateralManager) {
        return ICollateralManager(requireAndGetAddress(CONTRACT_COLLATERALMANAGER));
    }

    function debtSnapshotStaleTime() external view returns (uint) {
        return getDebtSnapshotStaleTime();
    }

    function cachedDebt() external view returns (uint) {
        return _cachedDebt;
    }

    function cachedSynthDebt(bytes32 currencyKey) external view returns (uint) {
        return _cachedSynthDebt[currencyKey];
    }

    function cacheTimestamp() external view returns (uint) {
        return _cacheTimestamp;
    }

    function cacheInvalid() external view returns (bool) {
        return _cacheInvalid;
    }

    function _cacheStale(uint timestamp) internal view returns (bool) {
        // Note a 0 timestamp means that the cache is uninitialised.
        // We'll keep the check explicitly in case the stale time is
        // ever set to something higher than the current unix time (e.g. to turn off staleness).
        return getDebtSnapshotStaleTime() < block.timestamp - timestamp || timestamp == 0;
    }

    function cacheStale() external view returns (bool) {
        return _cacheStale(_cacheTimestamp);
    }

    function _issuedSynthValues(bytes32[] memory currencyKeys, uint[] memory rates) internal view returns (uint[] memory) {
        uint numValues = currencyKeys.length;
        uint[] memory values = new uint[](numValues);
        ISynth[] memory synths = issuer().getSynths(currencyKeys);

        for (uint i = 0; i < numValues; i++) {
            bytes32 key = currencyKeys[i];
            address synthAddress = address(synths[i]);
            require(synthAddress != address(0), "Synth does not exist");
            uint supply = IERC20(synthAddress).totalSupply();

            if (collateralManager().isSynthManaged(key)) {
                uint collateralIssued = collateralManager().long(key);

                // this is an edge case --
                // if a synth other than sUSD is only issued by non SNX collateral
                // the long value will exceed the supply if there was a minting fee,
                // so we check explicitly and 0 it out to prevent
                // a safesub overflow.

                if (collateralIssued > supply) {
                    supply = 0;
                } else {
                    supply = supply.sub(collateralIssued);
                }
            }

            bool isSUSD = key == sUSD;
            if (isSUSD || key == sETH) {
                IEtherCollateral etherCollateralContract = isSUSD
                    ? IEtherCollateral(address(etherCollateralsUSD()))
                    : etherCollateral();
                uint etherCollateralSupply = etherCollateralContract.totalIssuedSynths();
                supply = supply.sub(etherCollateralSupply);
            }

            values[i] = supply.multiplyDecimalRound(rates[i]);
        }
        return values;
    }

    function _currentSynthDebts(bytes32[] memory currencyKeys)
        internal
        view
        returns (uint[] memory snxIssuedDebts, bool anyRateIsInvalid)
    {
        (uint[] memory rates, bool isInvalid) = exchangeRates().ratesAndInvalidForCurrencies(currencyKeys);
        return (_issuedSynthValues(currencyKeys, rates), isInvalid);
    }

    function currentSynthDebts(bytes32[] calldata currencyKeys)
        external
        view
        returns (uint[] memory debtValues, bool anyRateIsInvalid)
    {
        return _currentSynthDebts(currencyKeys);
    }

    function _cachedSynthDebts(bytes32[] memory currencyKeys) internal view returns (uint[] memory) {
        uint numKeys = currencyKeys.length;
        uint[] memory debts = new uint[](numKeys);
        for (uint i = 0; i < numKeys; i++) {
            debts[i] = _cachedSynthDebt[currencyKeys[i]];
        }
        return debts;
    }

    function cachedSynthDebts(bytes32[] calldata currencyKeys) external view returns (uint[] memory snxIssuedDebts) {
        return _cachedSynthDebts(currencyKeys);
    }

    function _currentDebt() internal view returns (uint debt, bool anyRateIsInvalid) {
        (uint[] memory values, bool isInvalid) = _currentSynthDebts(issuer().availableCurrencyKeys());
        uint numValues = values.length;
        uint total;
        for (uint i; i < numValues; i++) {
            total = total.add(values[i]);
        }

        // subtract the USD value of all shorts.
        (uint susdValue, bool shortInvalid) = collateralManager().totalShort();

        total = total.sub(susdValue);

        isInvalid = isInvalid || shortInvalid;

        return (total, isInvalid);
    }

    function currentDebt() external view returns (uint debt, bool anyRateIsInvalid) {
        return _currentDebt();
    }

    function cacheInfo()
        external
        view
        returns (
            uint debt,
            uint timestamp,
            bool isInvalid,
            bool isStale
        )
    {
        uint time = _cacheTimestamp;
        return (_cachedDebt, time, _cacheInvalid, _cacheStale(time));
    }

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

    // This function exists in case a synth is ever somehow removed without its snapshot being updated.
    function purgeCachedSynthDebt(bytes32 currencyKey) external onlyOwner {
        require(issuer().synths(currencyKey) == ISynth(0), "Synth exists");
        delete _cachedSynthDebt[currencyKey];
    }

    function takeDebtSnapshot() external requireSystemActiveIfNotOwner {
        bytes32[] memory currencyKeys = issuer().availableCurrencyKeys();
        (uint[] memory values, bool isInvalid) = _currentSynthDebts(currencyKeys);

        // Subtract the USD value of all shorts.
        (uint shortValue, ) = collateralManager().totalShort();

        uint numValues = values.length;
        uint snxCollateralDebt;
        for (uint i; i < numValues; i++) {
            uint value = values[i];
            snxCollateralDebt = snxCollateralDebt.add(value);
            _cachedSynthDebt[currencyKeys[i]] = value;
        }
        _cachedDebt = snxCollateralDebt.sub(shortValue);
        _cacheTimestamp = block.timestamp;
        emit DebtCacheUpdated(snxCollateralDebt);
        emit DebtCacheSnapshotTaken(block.timestamp);

        // (in)validate the cache if necessary
        _updateDebtCacheValidity(isInvalid);
    }

    function updateCachedSynthDebts(bytes32[] calldata currencyKeys) external requireSystemActiveIfNotOwner {
        (uint[] memory rates, bool anyRateInvalid) = exchangeRates().ratesAndInvalidForCurrencies(currencyKeys);
        _updateCachedSynthDebtsWithRates(currencyKeys, rates, anyRateInvalid);
    }

    function updateCachedSynthDebtWithRate(bytes32 currencyKey, uint currencyRate) external onlyIssuer {
        bytes32[] memory synthKeyArray = new bytes32[](1);
        synthKeyArray[0] = currencyKey;
        uint[] memory synthRateArray = new uint[](1);
        synthRateArray[0] = currencyRate;
        _updateCachedSynthDebtsWithRates(synthKeyArray, synthRateArray, false);
    }

    function updateCachedSynthDebtsWithRates(bytes32[] calldata currencyKeys, uint[] calldata currencyRates)
        external
        onlyIssuerOrExchanger
    {
        _updateCachedSynthDebtsWithRates(currencyKeys, currencyRates, false);
    }

    function updateDebtCacheValidity(bool currentlyInvalid) external onlyIssuer {
        _updateDebtCacheValidity(currentlyInvalid);
    }

    /* ========== INTERNAL FUNCTIONS ========== */

    function _updateDebtCacheValidity(bool currentlyInvalid) internal {
        if (_cacheInvalid != currentlyInvalid) {
            _cacheInvalid = currentlyInvalid;
            emit DebtCacheValidityChanged(currentlyInvalid);
        }
    }

    function _updateCachedSynthDebtsWithRates(
        bytes32[] memory currencyKeys,
        uint[] memory currentRates,
        bool anyRateIsInvalid
    ) internal {
        uint numKeys = currencyKeys.length;
        require(numKeys == currentRates.length, "Input array lengths differ");

        // Update the cached values for each synth, saving the sums as we go.
        uint cachedSum;
        uint currentSum;
        uint[] memory currentValues = _issuedSynthValues(currencyKeys, currentRates);
        for (uint i = 0; i < numKeys; i++) {
            bytes32 key = currencyKeys[i];
            uint currentSynthDebt = currentValues[i];
            cachedSum = cachedSum.add(_cachedSynthDebt[key]);
            currentSum = currentSum.add(currentSynthDebt);
            _cachedSynthDebt[key] = currentSynthDebt;
        }

        // Compute the difference and apply it to the snapshot
        if (cachedSum != currentSum) {
            uint debt = _cachedDebt;
            // This requirement should never fail, as the total debt snapshot is the sum of the individual synth
            // debt snapshots.
            require(cachedSum <= debt, "Cached synth sum exceeds total debt");
            debt = debt.sub(cachedSum).add(currentSum);
            _cachedDebt = debt;
            emit DebtCacheUpdated(debt);
        }

        // A partial update can invalidate the debt cache, but a full snapshot must be performed in order
        // to re-validate it.
        if (anyRateIsInvalid) {
            _updateDebtCacheValidity(anyRateIsInvalid);
        }
    }

    /* ========== MODIFIERS ========== */

    function _requireSystemActiveIfNotOwner() internal view {
        if (msg.sender != owner) {
            systemStatus().requireSystemActive();
        }
    }

    modifier requireSystemActiveIfNotOwner() {
        _requireSystemActiveIfNotOwner();
        _;
    }

    function _onlyIssuer() internal view {
        require(msg.sender == address(issuer()), "Sender is not Issuer");
    }

    modifier onlyIssuer() {
        _onlyIssuer();
        _;
    }

    function _onlyIssuerOrExchanger() internal view {
        require(msg.sender == address(issuer()) || msg.sender == address(exchanger()), "Sender is not Issuer or Exchanger");
    }

    modifier onlyIssuerOrExchanger() {
        _onlyIssuerOrExchanger();
        _;
    }

    /* ========== EVENTS ========== */

    event DebtCacheUpdated(uint cachedDebt);
    event DebtCacheSnapshotTaken(uint timestamp);
    event DebtCacheValidityChanged(bool indexed isInvalid);
}