/**
 *Submitted for verification at Etherscan.io on 2020-04-17
*/

pragma solidity ^0.5.16;

interface V1PriceOracleInterface {
    function assetPrices(address asset) external view returns (uint);
}

contract PriceOracleProxy is PriceOracle {
    /// @notice Indicator that this is a PriceOracle contract (for inspection)
    bool public constant isPriceOracle = true;

    /// @notice The v1 price oracle, which will continue to serve prices for v1 assets
    V1PriceOracleInterface public v1PriceOracle;

    /// @notice Address of the guardian, which may set the SAI price once
    address public guardian;

    /// @notice Address of the cEther contract, which has a constant price
    address public cEthAddress;

    /// @notice Address of the cUSDC contract, which we hand pick a key for
    address public cUsdcAddress;

    /// @notice Address of the cUSDT contract, which uses the cUSDC price
    address public cUsdtAddress;

    /// @notice Address of the cSAI contract, which may have its price set
    address public cSaiAddress;

    /// @notice Address of the cDAI contract, which we hand pick a key for
    address public cDaiAddress;

    /// @notice Handpicked key for USDC
    address public constant usdcOracleKey = address(1);

    /// @notice Handpicked key for DAI
    address public constant daiOracleKey = address(2);

    /// @notice Frozen SAI price (or 0 if not set yet)
    uint public saiPrice;

    /**
     * @param guardian_ The address of the guardian, which may set the SAI price once
     * @param v1PriceOracle_ The address of the v1 price oracle, which will continue to operate and hold prices for collateral assets
     * @param cEthAddress_ The address of cETH, which will return a constant 1e18, since all prices relative to ether
     * @param cUsdcAddress_ The address of cUSDC, which will be read from a special oracle key
     * @param cSaiAddress_ The address of cSAI, which may be read directly from storage
     * @param cDaiAddress_ The address of cDAI, which will be read from a special oracle key
     * @param cUsdtAddress_ The address of cUSDT, which uses the cUSDC price
     */
    constructor(address guardian_,
                address v1PriceOracle_,
                address cEthAddress_,
                address cUsdcAddress_,
                address cSaiAddress_,
                address cDaiAddress_,
                address cUsdtAddress_) public {
        guardian = guardian_;
        v1PriceOracle = V1PriceOracleInterface(v1PriceOracle_);

        cEthAddress = cEthAddress_;
        cUsdcAddress = cUsdcAddress_;
        cSaiAddress = cSaiAddress_;
        cDaiAddress = cDaiAddress_;
        cUsdtAddress = cUsdtAddress_;
    }

    /**
     * @notice Get the underlying price of a listed cToken asset
     * @param cToken The cToken to get the underlying price of
     * @return The underlying asset price mantissa (scaled by 1e18)
     */
    function getUnderlyingPrice(CToken cToken) public view returns (uint) {
        address cTokenAddress = address(cToken);

        if (cTokenAddress == cEthAddress) {
            // ether always worth 1
            return 1e18;
        }

        if (cTokenAddress == cUsdcAddress || cTokenAddress == cUsdtAddress) {
            return v1PriceOracle.assetPrices(usdcOracleKey);
        }

        if (cTokenAddress == cDaiAddress) {
            return v1PriceOracle.assetPrices(daiOracleKey);
        }

        if (cTokenAddress == cSaiAddress) {
            // use the frozen SAI price if set, otherwise use the DAI price
            return saiPrice > 0 ? saiPrice : v1PriceOracle.assetPrices(daiOracleKey);
        }

        // otherwise just read from v1 oracle
        address underlying = CErc20(cTokenAddress).underlying();
        return v1PriceOracle.assetPrices(underlying);
    }

    /**
     * @notice Set the price of SAI, permanently
     * @param price The price for SAI
     */
    function setSaiPrice(uint price) public {
        require(msg.sender == guardian, "only guardian may set the SAI price");
        require(saiPrice == 0, "SAI price may only be set once");
        require(price < 0.1e18, "SAI price must be < 0.1 ETH");
        saiPrice = price;
    }
}