// Base interface.
interface IChecker {
    function check(address passerby, bytes memory data) external view;
}

// Simple Checker for base use cases.
abstract contract SimpleChecker is IChecker {
    function check(address passerby, bytes memory data) external view virtual {
        _check(passerby, data);
    }
   
    function _check(address passerby, bytes memory data) internal view virtual;
}

// Advanced Checker for complex flows
// Used MAIN instead of CONTINUE for
// PRE-MAIN-POST and main check can be done >= 1 times.
abstract contract AdvancedChecker is IChecker {
    enum Phase { PRE, MAIN, POST }
    
    struct CheckStatus {
        bool preExecuted;
        bool mainExecuted;
        bool postExecuted;
    }
    
    mapping(address => CheckStatus) public checkStatus;
    uint8 public configFlags;
    
    function check(address passerby, bytes memory data) external view override {
        if (!_shouldSkipPhase(Phase.PRE)) {
            _checkPre(passerby, data);
        }
        _checkMain(passerby, data);
        if (!_shouldSkipPhase(Phase.POST)) {
            _checkPost(passerby, data);
        }
    }
    
    function _checkPre(address passerby, bytes memory data) internal view virtual {}
    function _checkMain(address passerby, bytes memory data) internal view virtual;
    function _checkPost(address passerby, bytes memory data) internal view virtual {}
}

// Factory pattern for checker creation.
contract CheckerFactory {
    function createSimpleChecker() external returns (address);
    function createAdvancedChecker(uint8 configFlags) external returns (address);
}

// Modified Excubia base.
abstract contract Excubia is IExcubia {
    IChecker public immutable checker;
    
    constructor(IChecker _checker) {
        checker = _checker;
    }
    
    function pass(address passerby, bytes calldata data) external virtual onlyGate {
        checker.check(passerby, data);
        emit GatePassed(passerby, gate);
    }
}