// SPDX-License-Identifier: MIT

pragma solidity 0.8.30;

import "@openzeppelin/contracts/utils/math/Math.sol";
import "../interfaces/IOrderMixin.sol";
import "../interfaces/IAmountGetter.sol";

/**
 * A range limit order is a strategy used to sell an asset within a specified price range.
 * For instance, suppose you anticipate the value of ETH to increase in the next week from its
 * current worth of 3000 DAI to a minimum of 4000 DAI.
 * In that case, you can create an ETH -> DAI limit order within the price range of 3000 -> 4000.
 * For example, you could create an order to sell 10 ETH within that price range.
 *
 * When someone places a bid for the entire limit order, they may purchase it all at once at
 * an average price of 3500 DAI. Alternatively, the limit order may be executed in portions.
 * For instance, the buyer might purchase 1 ETH for 3050 DAI, then another 1 ETH for 3150 DAI, and so on.
 *
 * Function of the changing price of makerAsset tokens in takerAsset tokens by the filling amount of makerAsset tokens in order:
 *      priceEnd - priceStart
 * y = ----------------------- * x + priceStart
 *           totalAmount
 */
contract RangeAmountCalculator is IAmountGetter {
    error IncorrectRange();

    modifier correctPrices(uint256 priceStart, uint256 priceEnd) {
        if (priceEnd <= priceStart) revert IncorrectRange();
        _;
    }

    function getTakingAmount(
        IOrderMixin.Order calldata order,
        bytes calldata /* extension */,
        bytes32 /* orderHash */,
        address /* taker */,
        uint256 makingAmount,
        uint256 remainingMakingAmount,
        bytes calldata extraData
    ) external pure returns (uint256) {
        (
            uint256 priceStart,
            uint256 priceEnd
        ) = abi.decode(extraData, (uint256, uint256));
        return getRangeTakerAmount(priceStart, priceEnd, order.makingAmount, makingAmount, remainingMakingAmount);
    }

    function getMakingAmount(
        IOrderMixin.Order calldata order,
        bytes calldata /* extension */,
        bytes32 /* orderHash */,
        address /* taker */,
        uint256 takingAmount,
        uint256 remainingMakingAmount,
        bytes calldata extraData
    ) external pure returns (uint256) {
        (
            uint256 priceStart,
            uint256 priceEnd
        ) = abi.decode(extraData, (uint256, uint256));
        return getRangeMakerAmount(priceStart, priceEnd, order.makingAmount, takingAmount, remainingMakingAmount);
    }

    function getRangeTakerAmount(
        uint256 priceStart,
        uint256 priceEnd,
        uint256 orderMakingAmount,
        uint256 makingAmount,
        uint256 remainingMakingAmount
    ) public correctPrices(priceStart, priceEnd) pure returns(uint256) {
        uint256 alreadyFilledMakingAmount = orderMakingAmount - remainingMakingAmount;
        /**
         * rangeTakerAmount = (
         *       f(makerAmountFilled) + f(makerAmountFilled + fillAmount)
         *   ) * fillAmount / 2 / 1e18
         *
         *  scaling to 1e18 happens to have better price accuracy
         */
        return (
            (priceEnd - priceStart) * (2 * alreadyFilledMakingAmount + makingAmount) / orderMakingAmount +
            2 * priceStart
        ) * makingAmount / 2e18;
    }

    function getRangeMakerAmount(
        uint256 priceStart,
        uint256 priceEnd,
        uint256 orderMakingAmount,
        uint256 takingAmount,
        uint256 remainingMakingAmount
    ) public correctPrices(priceStart, priceEnd) pure returns(uint256) {
        uint256 alreadyFilledMakingAmount = orderMakingAmount - remainingMakingAmount;
        uint256 b = priceStart;
        uint256 k = (priceEnd - priceStart) * 1e18 / orderMakingAmount;
        uint256 bDivK = priceStart * orderMakingAmount / (priceEnd - priceStart);
        return (Math.sqrt(
            (
                b * bDivK +
                alreadyFilledMakingAmount * (2 * b + k * alreadyFilledMakingAmount / 1e18) +
                2 * takingAmount * 1e18
            ) / k * 1e18
        ) - bDivK) - alreadyFilledMakingAmount;
    }
}