Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract Core {
    event Swap(
        address indexed sender,
        address tokenIn,
        address tokenOut,
        uint256 amountIn,
        uint256 amountOut,
        uint256 buyPrice,
        uint256 sellPrice
    );
    event LiquidityAdded(
        address indexed provider,
        address token,
        uint256 amount
    );
    event LiquidityRemoved(
        address indexed provider,
        address token,
        uint256 amount
    );
    event PriceUpdated(
        address indexed token,
        uint256 newPrice,
        uint256 newLiquidity
    );

    mapping(address => uint256) public liquidity;
    mapping(address => uint256) public tokenPrices;

    function addLiquidity(address token, uint256 amount) external {
        require(amount > 0, "Amount must be greater than zero");
        require(
            IERC20(token).transferFrom(msg.sender, address(this), amount),
            "Transfer failed"
        );
        liquidity[token] += amount;
        emit LiquidityAdded(msg.sender, token, amount);
    }

    function removeLiquidity(address token, uint256 amount) external {
        require(liquidity[token] >= amount, "Insufficient liquidity");
        liquidity[token] -= amount;
        require(IERC20(token).transfer(msg.sender, amount), "Transfer failed");
        emit LiquidityRemoved(msg.sender, token, amount);
    }

    function getLiquidity(address token) external view returns (uint256) {
        return liquidity[token];
    }

    function setPriceAndLiquidity(address token, uint256 newPrice, uint256 newLiquidity) external {
        require(newLiquidity > 0, "Liquidity must be greater than zero");
        tokenPrices[token] = newPrice;
        liquidity[token] = newLiquidity;
        emit PriceUpdated(token, newPrice, newLiquidity);
    }

    function setPriceAndAutoSetLiquidity(address token, uint256 newPrice) external {
        require(newPrice > 0, "Price must be greater than zero");
        tokenPrices[token] = newPrice;
        uint256 newLiquidity = 1e18 / newPrice;
        liquidity[token] = newLiquidity;
        emit PriceUpdated(token, newPrice, newLiquidity);
    }

    function swap(
        address tokenIn,
        address tokenOut,
        uint256 amountIn
    ) external returns (uint256 amountOut) {
        require(
            tokenIn != address(0) && tokenOut != address(0),
            "Invalid token address"
        );
        require(amountIn > 0, "Amount must be greater than zero");
        require(
            liquidity[tokenIn] > 0 && liquidity[tokenOut] > 0,
            "Insufficient liquidity"
        );

        uint256 reserveIn = liquidity[tokenIn];
        uint256 reserveOut = liquidity[tokenOut];
        require(reserveIn > 0 && reserveOut > 0, "Invalid reserves");

        // Calculate buy price and sell price before the swap
        uint256 buyPrice = (reserveOut * 1e18) / reserveIn;
        uint256 sellPrice = (reserveIn * 1e18) / reserveOut;

        // Swap formula: x * y = k
        uint256 amountInWithFee = (amountIn * 997) / 1000; // 0.3% fee
        amountOut = (amountInWithFee * reserveOut) / (reserveIn + amountInWithFee);
        require(amountOut > 0, "Swap amount must be greater than zero");

        // Update liquidity
        liquidity[tokenIn] += amountIn;
        liquidity[tokenOut] -= amountOut;

        require(
            IERC20(tokenIn).transferFrom(msg.sender, address(this), amountIn),
            "Token transfer failed"
        );
        require(
            IERC20(tokenOut).transfer(msg.sender, amountOut),
            "Token transfer failed"
        );

        emit Swap(msg.sender, tokenIn, tokenOut, amountIn, amountOut, buyPrice, sellPrice);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.1.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.20;

/**
 * @dev Interface of the ERC-20 standard as defined in the ERC.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the value of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the value of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves a `value` amount of tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 value) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets a `value` amount of tokens as the allowance of `spender` over the
     * caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 value) external returns (bool);

    /**
     * @dev Moves a `value` amount of tokens from `from` to `to` using the
     * allowance mechanism. `value` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 value) external returns (bool);
}