// SPDX-License-Identifier: MIT

pragma solidity =0.8.18;

import "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import "@openzeppelin/contracts-upgradeable/metatx/ERC2771ContextUpgradeable.sol";

import "../../SomaGuard/utils/GuardHelper.sol";
import "../../SecurityTokens/ERC20/utils/ERC20Helper.sol";
import "../../SecurityTokens/extensions/ERC20Security.sol";

import "./interfaces/ISomaSwapPair.sol";
import "./libraries/Math.sol";
import "./libraries/UQ112x112.sol";
import "./interfaces/ISomaSwapFactory.sol";
import "./interfaces/ISomaSwapCallee.sol";

/**
 * @notice Implementation of the {ISomaSwapPair} interface.
 */
contract SomaSwapPair is ISomaSwapPair, ERC20Security {
    using SafeMath for uint256;
    using UQ112x112 for uint224;

    /**
     * @inheritdoc ISomaSwapPair
     */
    uint256 public constant override MINIMUM_LIQUIDITY = 10 ** 3;

    bytes4 private constant SELECTOR = bytes4(keccak256(bytes("transfer(address,uint256)")));

    /**
     * @inheritdoc ISomaSwapPair
     */
    address public override factory;

    /**
     * @inheritdoc ISomaSwapPair
     */
    address public override token0;

    /**
     * @inheritdoc ISomaSwapPair
     */
    address public override token1;

    uint112 private reserve0; // uses single storage slot, accessible via getReserves
    uint112 private reserve1; // uses single storage slot, accessible via getReserves
    uint32 private blockTimestampLast; // uses single storage slot, accessible via getReserves

    /**
     * @inheritdoc ISomaSwapPair
     */
    uint256 public override price0CumulativeLast;

    /**
     * @inheritdoc ISomaSwapPair
     */
    uint256 public override price1CumulativeLast;

    /**
     * @inheritdoc ISomaSwapPair
     */
    uint256 public override kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event

    uint256 private locked;

    /**
     * @notice Swap Data structure. Helper structure to save variable space.
     * @param balance0 The pair address' balance of token0 before reserves are updated.
     * @param balance1 The pair address' balance of token1 before reserves are updated.
     * @param amount0In The amount of token0 swapped.
     * @param amount1In The amount of token1 swapped.
     */
    struct SwapData {
        uint256 balance0;
        uint256 balance1;
        uint256 amount0In;
        uint256 amount1In;
    }

    /**
     * @notice Modifier to ensure the contract is not locked upon a function call.
     */
    modifier lock() {
        require(locked == 0, "SomaSwap: LOCKED");
        locked = 1;
        _;
        locked = 0;
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev Called once by the factory at time of deployment
     */
    function initialize(address _token0, address _token1) external override initializer {
        // need to avoid _msgSender here so that we define the factory and _msgSender can be used
        factory = msg.sender;
        token0 = _token0;
        token1 = _token1;

        string memory _name = "SOMASwap";
        string memory _symbol;

        {
            string memory token0Name = IERC20Metadata(token0).name();
            string memory token1Name = IERC20Metadata(token1).name();
            _name = string(
                abi.encodePacked(
                    _name,
                    bytes(token0Name).length > 0 || bytes(token1Name).length > 0 ? ": " : "",
                    bytes(token0Name).length > 0 ? token0Name : "",
                    bytes(token0Name).length > 0 && bytes(token1Name).length > 0 ? " - " : "",
                    bytes(token1Name).length > 0 ? token1Name : ""
                )
            );
        }

        {
            string memory token0Symbol = IERC20Metadata(token0).symbol();
            string memory token1Symbol = IERC20Metadata(token1).symbol();
            _symbol = string(
                abi.encodePacked(
                    bytes(token0Symbol).length > 0 ? token0Symbol : "",
                    bytes(token0Symbol).length > 0 && bytes(token1Symbol).length > 0 ? "-" : "",
                    bytes(token1Symbol).length > 0 ? token1Symbol : ""
                )
            );
        }

        __ERC20Security_init("SOMAswap", _name, _symbol);
    }

    /**
     * @notice Checks if SomaSwapPair inherits a given contract interface.
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(ISomaSwapPair).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @notice Returns the required privileges.
     */
    function requiredPrivileges() public view virtual override returns (bytes32) {
        bytes32 token0Privileges = GuardHelper.requiredPrivileges(token0);
        bytes32 token1Privileges = GuardHelper.requiredPrivileges(token1);
        return GuardHelper.mergePrivileges(token0Privileges, token1Privileges, super.requiredPrivileges());
    }

    /**
     * @inheritdoc ISomaSwapPair
     */
    function getReserves()
        public
        view
        override
        returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast)
    {
        _reserve0 = reserve0;
        _reserve1 = reserve1;
        _blockTimestampLast = blockTimestampLast;
    }

    function _safeTransfer(address token, address to, uint256 value) private {
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "SomaSwap: TRANSFER_FAILED");
    }

    // update reserves and, on the first call per block, price accumulators
    function _update(uint256 balance0, uint256 balance1, uint112 _reserve0, uint112 _reserve1) private {
        require(balance0 <= type(uint112).max && balance1 <= type(uint112).max, "SomaSwap: OVERFLOW");
        // slither-disable-next-line weak-prng
        uint32 blockTimestamp = uint32(block.timestamp % 2 ** 32);
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
        if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
            // * never overflows, and + overflow is desired
            price0CumulativeLast += uint256(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) * timeElapsed;
            price1CumulativeLast += uint256(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) * timeElapsed;
        }
        reserve0 = uint112(balance0);
        reserve1 = uint112(balance1);
        blockTimestampLast = blockTimestamp;
        emit Sync(reserve0, reserve1);
    }

    // if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
    function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
        address feeTo = ISomaSwapFactory(factory).feeTo();
        feeOn = feeTo != address(0);
        uint256 _kLast = kLast; // gas savings
        if (feeOn) {
            if (_kLast != 0) {
                uint256 rootK = Math.sqrt(uint256(_reserve0).mul(_reserve1));
                uint256 rootKLast = Math.sqrt(_kLast);
                if (rootK > rootKLast) {
                    uint256 numerator = totalSupply().mul(rootK.sub(rootKLast));
                    uint256 denominator = rootK.mul(5).add(rootKLast);
                    uint256 liquidity = numerator / denominator;
                    if (liquidity > 0) _mint(feeTo, liquidity);
                }
            }
        } else if (_kLast != 0) {
            kLast = 0;
        }
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev This low-level function should be called from a contract which performs important safety checks
     */
    function mint(address to) external override lock returns (uint256 liquidity) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        uint256 balance0 = IERC20(token0).balanceOf(address(this));
        uint256 balance1 = IERC20(token1).balanceOf(address(this));
        uint256 amount0 = balance0.sub(_reserve0);
        uint256 amount1 = balance1.sub(_reserve1);

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint256 _totalSupply = totalSupply(); // gas savings, must be defined here since totalSupply can update in _mintFee
        if (_totalSupply == 0) {
            liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
            // Here we mint to the factory instead of self, because the burn requires burning all of tokens on self
            _mint(factory, MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
        } else {
            liquidity = Math.min(amount0.mul(_totalSupply) / _reserve0, amount1.mul(_totalSupply) / _reserve1);
        }
        require(liquidity > 0, "SomaSwap: INSUFFICIENT_LIQUIDITY_MINTED");
        _mint(to, liquidity);

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Mint(msg.sender, amount0, amount1);
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev This low-level function should be called from a contract which performs important safety checks
     */
    function burn(address to) external override lock returns (uint256 amount0, uint256 amount1) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        address _token0 = token0; // gas savings
        address _token1 = token1; // gas savings
        uint256 balance0 = IERC20(_token0).balanceOf(address(this));
        uint256 balance1 = IERC20(_token1).balanceOf(address(this));
        uint256 liquidity = balanceOf(address(this));

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint256 _totalSupply = totalSupply(); // gas savings, must be defined here since totalSupply can update in _mintFee
        amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
        amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
        require(amount0 > 0 && amount1 > 0, "SomaSwap: INSUFFICIENT_LIQUIDITY_BURNED");
        _burn(address(this), liquidity);
        // slither-disable-next-line reentrancy-no-eth
        _safeTransfer(_token0, to, amount0);
        // slither-disable-next-line reentrancy-no-eth
        _safeTransfer(_token1, to, amount1);
        balance0 = IERC20(_token0).balanceOf(address(this));
        balance1 = IERC20(_token1).balanceOf(address(this));

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Burn(msg.sender, amount0, amount1, to);
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev This low-level function should be called from a contract which performs important safety checks
     */
    //slither-disable-next-line external-function
    function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data)
        external
        override
        lock
        onlyApprovedPrivileges(_forwardSender())
    {
        require(amount0Out > 0 || amount1Out > 0, "SomaSwap: INSUFFICIENT_OUTPUT_AMOUNT");
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        require(amount0Out < _reserve0 && amount1Out < _reserve1, "SomaSwap: INSUFFICIENT_LIQUIDITY");

        SwapData memory _data;
        {
            // scope for _token{0,1}, avoids stack too deep errors
            address _token0 = token0;
            address _token1 = token1;
            require(to != _token0 && to != _token1, "SomaSwap: INVALID_TO");
            // slither-disable-next-line reentrancy-no-eth
            if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
            // slither-disable-next-line reentrancy-no-eth
            if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
            // slither-disable-next-line reentrancy-no-eth
            if (data.length > 0) ISomaSwapCallee(to).somaSwapCall(msg.sender, amount0Out, amount1Out, data);
            _data.balance0 = IERC20(_token0).balanceOf(address(this));
            _data.balance1 = IERC20(_token1).balanceOf(address(this));
        }
        _data.amount0In = _data.balance0 > _reserve0 - amount0Out ? _data.balance0 - (_reserve0 - amount0Out) : 0;
        _data.amount1In = _data.balance1 > _reserve1 - amount1Out ? _data.balance1 - (_reserve1 - amount1Out) : 0;
        require(_data.amount0In > 0 || _data.amount1In > 0, "SomaSwap: INSUFFICIENT_INPUT_AMOUNT");
        {
            // scope for reserve{0,1}Adjusted, avoids stack too deep errors
            uint256 balance0Adjusted = _data.balance0.mul(1000).sub(_data.amount0In.mul(3));
            uint256 balance1Adjusted = _data.balance1.mul(1000).sub(_data.amount1In.mul(3));
            require(
                balance0Adjusted.mul(balance1Adjusted) >= uint256(_reserve0).mul(_reserve1).mul(1000 ** 2),
                "SomaSwap: K"
            );
        }

        _update(_data.balance0, _data.balance1, _reserve0, _reserve1);
        emit Swap(msg.sender, _data.amount0In, _data.amount1In, amount0Out, amount1Out, to);
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev Force balances to match reserves
     */
    function skim(address to) external override lock {
        address _token0 = token0; // gas savings
        address _token1 = token1; // gas savings
        _safeTransfer(_token0, to, IERC20(_token0).balanceOf(address(this)).sub(reserve0));
        _safeTransfer(_token1, to, IERC20(_token1).balanceOf(address(this)).sub(reserve1));
    }

    /**
     * @inheritdoc ISomaSwapPair
     * @dev Force reserves to match balances
     */
    function sync() external override lock {
        _update(IERC20(token0).balanceOf(address(this)), IERC20(token1).balanceOf(address(this)), reserve0, reserve1);
    }

    function _forwardSender() private view returns (address sender) {
        if (ISomaSwapFactory(factory).isRouter(msg.sender)) {
            // The assembly code is more direct than the Solidity version using `abi.decode`.
            assembly {
                sender := shr(96, calldataload(sub(calldatasize(), 20)))
            }
        } else {
            sender = msg.sender;
        }
    }
}