/**
 * @fileoverview Structured errors and Express helpers.
 * @module errors
 */

import { createDebugger } from './debug/logger.js';
import { getTraceId } from './debug/trace-context.js';

const log = createDebugger('app');

/**
 * Operational error with HTTP status and machine-readable code.
 */
export class AppError extends Error {
  /**
   * @param {string} message - Human-readable error.
   * @param {object} [options]
   * @param {number} [options.status=500] - HTTP status code.
   * @param {string} [options.code='INTERNAL_ERROR'] - Machine code.
   * @param {unknown} [options.details] - Optional structured details (safe for clients).
   */
  constructor(message, { status = 500, code = 'INTERNAL_ERROR', details } = {}) {
    super(message);
    this.name = 'AppError';
    this.status = status;
    this.code = code;
    this.details = details;
  }
}

/**
 * Wrap an async Express handler so rejected promises reach the error middleware.
 *
 * @param {(req: import('express').Request, res: import('express').Response, next: import('express').NextFunction) => Promise<unknown>} fn
 * @returns {import('express').RequestHandler}
 */
export function asyncHandler(fn) {
  return (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
}

/**
 * Send a JSON error response. Logs server errors when debug is enabled.
 *
 * @param {import('express').Response} res
 * @param {Error|AppError} err
 * @returns {void}
 */
export function sendError(res, err) {
  const status = err instanceof AppError ? err.status : 500;
  const code = err instanceof AppError ? err.code : 'INTERNAL_ERROR';
  const message = err?.message || 'Internal server error';
  const details = err instanceof AppError ? err.details : undefined;
  const traceId = getTraceId();

  if (status >= 500) {
    log.error('request failed', {
      status,
      code,
      message,
      traceId,
      stack: err?.stack,
    });
  } else {
    log.debug('client error', { status, code, message, traceId });
  }

  res.status(status).json({
    error: message,
    code,
    ...(details !== undefined ? { details } : {}),
    ...(traceId ? { traceId } : {}),
  });
}