// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @title IPermit2
 * @dev Interface for a flexible permit system that extends ERC20 tokens to support permits in tokens lacking native permit functionality.
 */
interface IPermit2 {
    /**
     * @dev Struct for holding permit details.
     * @param token ERC20 token address for which the permit is issued.
     * @param amount The maximum amount allowed to spend.
     * @param expiration Timestamp until which the permit is valid.
     * @param nonce An incrementing value for each signature, unique per owner, token, and spender.
     */
    struct PermitDetails {
        address token;
        uint160 amount;
        uint48 expiration;
        uint48 nonce;
    }

    /**
     * @dev Struct for a single token allowance permit.
     * @param details Permit details including token, amount, expiration, and nonce.
     * @param spender Address authorized to spend the tokens.
     * @param sigDeadline Deadline for the permit signature, ensuring timeliness of the permit.
     */
    struct PermitSingle {
        PermitDetails details;
        address spender;
        uint256 sigDeadline;
    }

    /**
     * @dev Struct for packed allowance data to optimize storage.
     * @param amount Amount allowed.
     * @param expiration Permission expiry timestamp.
     * @param nonce Unique incrementing value for tracking allowances.
     */
    struct PackedAllowance {
        uint160 amount;
        uint48 expiration;
        uint48 nonce;
    }

    /**
     * @notice Executes a token transfer from one address to another.
     * @param user The token owner's address.
     * @param spender The address authorized to spend the tokens.
     * @param amount The amount of tokens to transfer.
     * @param token The address of the token being transferred.
     */
    function transferFrom(address user, address spender, uint160 amount, address token) external;

    /**
     * @notice Issues a permit for spending tokens via a signed authorization.
     * @param owner The token owner's address.
     * @param permitSingle Struct containing the permit details.
     * @param signature The signature proving the owner authorized the permit.
     */
    function permit(address owner, PermitSingle memory permitSingle, bytes calldata signature) external;

    /**
     * @notice Retrieves the allowance details between a token owner and spender.
     * @param user The token owner's address.
     * @param token The token address.
     * @param spender The spender's address.
     * @return The packed allowance details.
     */
    function allowance(address user, address token, address spender) external view returns (PackedAllowance memory);

    /**
     * @notice Approves the spender to use up to amount of the specified token up until the expiration
     * @param token The token to approve
     * @param spender The spender address to approve
     * @param amount The approved amount of the token
     * @param expiration The timestamp at which the approval is no longer valid
     * @dev The packed allowance also holds a nonce, which will stay unchanged in approve
     * @dev Setting amount to type(uint160).max sets an unlimited approval
     */
    function approve(address token, address spender, uint160 amount, uint48 expiration) external;
}