<?php

declare(strict_types=1);

namespace App\Service;

use Symfony\Component\HttpFoundation\RequestStack;

/**
 * Generates and tracks error reference codes for user-facing error messages.
 *
 * Produces deterministic codes based on the current request ID, allowing users
 * to report error codes to support staff who can then search logs by the code.
 * The code format is E-XXXXXXXX (8 uppercase alphanumeric characters in base36).
 */
class ErrorCodeGenerator
{
    private ?string $errorCode = null;
    private bool $hasError = false;

    public function __construct(
        private readonly RequestStack $requestStack,
    ) {
    }

    /**
     * Returns the error code for the current request.
     *
     * Generates a deterministic code from the request ID on first call and
     * caches it for subsequent calls. Sequence suffixes like _1, _2 are
     * stripped before hashing to ensure all requests in a sequence share
     * the same error code.
     *
     * @return string|null The error code or null if no request context exists
     */
    public function getErrorCode(): ?string
    {
        if (null !== $this->errorCode) {
            return $this->errorCode;
        }

        $request = $this->requestStack->getMainRequest();
        if (null === $request) {
            return null;
        }

        $requestId = $request->attributes->get('request_id');
        if (null === $requestId) {
            return null;
        }

        $this->errorCode = $this->generateCode((string) $requestId);

        return $this->errorCode;
    }

    /**
     * Marks that an error has occurred during this request.
     *
     * Called by the ErrorCodeProcessor when a log entry with ERROR level
     * or higher is created.
     */
    public function markErrorOccurred(): void
    {
        $this->hasError = true;
    }

    /**
     * Checks whether an error has been logged during this request.
     *
     * @return bool True if an error has been logged, false otherwise
     */
    public function hasError(): bool
    {
        return $this->hasError;
    }

    /**
     * Generates an error code from a request ID.
     *
     * Strips sequence suffixes, hashes the normalized ID, and converts
     * to a base36 representation prefixed with E-.
     *
     * @param string $requestId The request ID to generate a code from
     *
     * @return string The generated error code in format E-XXXXXXXX
     */
    private function generateCode(string $requestId): string
    {
        $normalizedId = preg_replace('/_\d+$/', '', $requestId);
        $hash = md5((string) $normalizedId);
        $hexPart = substr($hash, 0, 12);
        $decimal = hexdec($hexPart);
        $base36 = strtoupper(base_convert((string) $decimal, 10, 36));
        $padded = str_pad($base36, 8, '0', STR_PAD_LEFT);

        return 'E-'.substr($padded, 0, 8);
    }
}