/// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

using AllowanceLib for AllowanceMap global;

struct AllowanceMap {
    // no direct access
    uint256 placeholder;
}

library AllowanceLib {
    function slot(
        AllowanceMap storage self,
        address account,
        address spender
    )
        internal
        pure
        returns (uint256 _slot)
    {
        assembly ("memory-safe") {
            mstore(0, account)
            mstore(0x20, self.slot)
            mstore(0x20, keccak256(0, 0x40))
            mstore(0, spender)
            _slot := keccak256(0, 0x40)
        }
    }

    function get(
        AllowanceMap storage self,
        address account,
        address spender
    )
        internal
        view
        returns (uint256 allowance)
    {
        uint256 _slot = self.slot(account, spender);
        assembly ("memory-safe") {
            allowance := sload(_slot)
        }
    }

    function set(
        AllowanceMap storage self,
        address account,
        address spender,
        uint256 allowance
    )
        internal
    {
        uint256 _slot = self.slot(account, spender);
        assembly ("memory-safe") {
            sstore(_slot, allowance)
        }
    }
}