// SPDX-License-Identifier: Apache-2.0
/*

  Copyright 2020 ZeroEx Intl.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

*/

pragma solidity ^0.6;
pragma experimental ABIEncoderV2;

import "./interfaces/IUniswapExchangeQuotes.sol";
import "./SamplerUtils.sol";


interface IUniswapExchangeFactory {

    /// @dev Get the exchange for a token.
    /// @param tokenAddress The address of the token contract.
    function getExchange(address tokenAddress)
        external
        view
        returns (address);
}


contract UniswapSampler is
    SamplerUtils
{
    /// @dev Gas limit for Uniswap calls.
    uint256 constant private UNISWAP_CALL_GAS = 150e3; // 150k

    /// @dev Sample sell quotes from Uniswap.
    /// @param router Address of the Uniswap Router
    /// @param takerToken Address of the taker token (what to sell).
    /// @param makerToken Address of the maker token (what to buy).
    /// @param takerTokenAmounts Taker token sell amount for each sample.
    /// @return makerTokenAmounts Maker amounts bought at each taker token
    ///         amount.
    function sampleSellsFromUniswap(
        address router,
        address takerToken,
        address makerToken,
        uint256[] memory takerTokenAmounts
    )
        public
        view
        returns (uint256[] memory makerTokenAmounts)
    {
        _assertValidPair(makerToken, takerToken);
        uint256 numSamples = takerTokenAmounts.length;
        makerTokenAmounts = new uint256[](numSamples);

        IUniswapExchangeQuotes takerTokenExchange = takerToken == address(0) ?
            IUniswapExchangeQuotes(0) : _getUniswapExchange(router, takerToken);
        IUniswapExchangeQuotes makerTokenExchange = makerToken == address(0) ?
            IUniswapExchangeQuotes(0) : _getUniswapExchange(router, makerToken);
        for (uint256 i = 0; i < numSamples; i++) {
            bool didSucceed = true;
            if (makerToken == address(0)) {
                (makerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                    address(takerTokenExchange),
                    takerTokenExchange.getTokenToEthInputPrice.selector,
                    takerTokenAmounts[i]
                );
            } else if (takerToken == address(0)) {
                (makerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                    address(makerTokenExchange),
                    makerTokenExchange.getEthToTokenInputPrice.selector,
                    takerTokenAmounts[i]
                );
            } else {
                uint256 ethBought;
                (ethBought, didSucceed) = _callUniswapExchangePriceFunction(
                    address(takerTokenExchange),
                    takerTokenExchange.getTokenToEthInputPrice.selector,
                    takerTokenAmounts[i]
                );
                if (ethBought != 0) {
                    (makerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                        address(makerTokenExchange),
                        makerTokenExchange.getEthToTokenInputPrice.selector,
                        ethBought
                    );
                } else {
                    makerTokenAmounts[i] = 0;
                }
            }
            // Break early if amounts are 0
            if (!didSucceed || makerTokenAmounts[i] == 0) {
                break;
            }
        }
    }

    /// @dev Sample buy quotes from Uniswap.
    /// @param takerToken Address of the taker token (what to sell).
    /// @param makerToken Address of the maker token (what to buy).
    /// @param makerTokenAmounts Maker token sell amount for each sample.
    /// @return takerTokenAmounts Taker amounts sold at each maker token
    ///         amount.
    function sampleBuysFromUniswap(
        address router,
        address takerToken,
        address makerToken,
        uint256[] memory makerTokenAmounts
    )
        public
        view
        returns (uint256[] memory takerTokenAmounts)
    {
        _assertValidPair(makerToken, takerToken);
        uint256 numSamples = makerTokenAmounts.length;
        takerTokenAmounts = new uint256[](numSamples);

        IUniswapExchangeQuotes takerTokenExchange = takerToken == address(0) ?
            IUniswapExchangeQuotes(0) : _getUniswapExchange(router, takerToken);
        IUniswapExchangeQuotes makerTokenExchange = makerToken == address(0) ?
            IUniswapExchangeQuotes(0) : _getUniswapExchange(router, makerToken);
        for (uint256 i = 0; i < numSamples; i++) {
            bool didSucceed = true;
            if (makerToken == address(0)) {
                (takerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                    address(takerTokenExchange),
                    takerTokenExchange.getTokenToEthOutputPrice.selector,
                    makerTokenAmounts[i]
                );
            } else if (takerToken == address(0)) {
                (takerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                    address(makerTokenExchange),
                    makerTokenExchange.getEthToTokenOutputPrice.selector,
                    makerTokenAmounts[i]
                );
            } else {
                uint256 ethSold;
                (ethSold, didSucceed) = _callUniswapExchangePriceFunction(
                    address(makerTokenExchange),
                    makerTokenExchange.getEthToTokenOutputPrice.selector,
                    makerTokenAmounts[i]
                );
                if (ethSold != 0) {
                    (takerTokenAmounts[i], didSucceed) = _callUniswapExchangePriceFunction(
                        address(takerTokenExchange),
                        takerTokenExchange.getTokenToEthOutputPrice.selector,
                        ethSold
                    );
                } else {
                    takerTokenAmounts[i] = 0;
                }
            }
            // Break early if amounts are 0
            if (!didSucceed || takerTokenAmounts[i] == 0) {
                break;
            }
        }
    }

    /// @dev Gracefully calls a Uniswap pricing function.
    /// @param uniswapExchangeAddress Address of an `IUniswapExchangeQuotes` exchange.
    /// @param functionSelector Selector of the target function.
    /// @param inputAmount Quantity parameter particular to the pricing function.
    /// @return outputAmount The returned amount from the function call. Will be
    ///         zero if the call fails or if `uniswapExchangeAddress` is zero.
    function _callUniswapExchangePriceFunction(
        address uniswapExchangeAddress,
        bytes4 functionSelector,
        uint256 inputAmount
    )
        private
        view
        returns (uint256 outputAmount, bool didSucceed)
    {
        if (uniswapExchangeAddress == address(0)) {
            return (outputAmount, didSucceed);
        }
        bytes memory resultData;
        (didSucceed, resultData) =
            uniswapExchangeAddress.staticcall.gas(UNISWAP_CALL_GAS)(
                abi.encodeWithSelector(
                    functionSelector,
                    inputAmount
                ));
        if (didSucceed) {
            outputAmount = abi.decode(resultData, (uint256));
        }
    }

    /// @dev Retrive an existing Uniswap exchange contract.
    ///      Throws if the exchange does not exist.
    /// @param router Address of the Uniswap router.
    /// @param tokenAddress Address of the token contract.
    /// @return exchange `IUniswapExchangeQuotes` for the token.
    function _getUniswapExchange(address router, address tokenAddress)
        private
        view
        returns (IUniswapExchangeQuotes exchange)
    {
        exchange = IUniswapExchangeQuotes(
            address(IUniswapExchangeFactory(router)
            .getExchange(tokenAddress))
        );
    }
}