import { HttpError } from "@nestia/fetcher";
import { HttpException } from "@nestjs/common";

import { Creator } from "../typings/Creator";

/**
 * Exception manager for HTTP server.
 *
 * `ExceptionManager` is an utility class who can insert or erase custom error
 * class with its conversion method to a regular {@link nest.HttpException}
 * instance.
 *
 * If you define an API function through {@link TypedRoute} or
 * {@link EncryptedRoute} instead of the basic router decorator functions like
 * {@link nest.Get} or {@link nest.Post} and the API function throws a custom
 * error whose class has been {@link ExceptionManager.insert inserted} in this
 * `EntityManager`, the error would be automatically converted to the regular
 * {@link nest.HttpException} instance by the {@link ExceptionManager.Closure}
 * function.
 *
 * Therefore, with this `ExceptionManager` and {@link TypedRoute} or
 * {@link EncryptedRoute}, you can manage your custom error classes much
 * systemtically. You can avoid 500 internal server error or hard coding
 * implementation about the custom error classes.
 *
 * Below error classes are defaultly configured in this `ExceptionManager`
 *
 * - `typia.TypeGuardError`
 * - `@nestia/fetcher.HttpError`
 *
 * @author Jeongho Nam - https://github.com/samchon
 */
export namespace ExceptionManager {
  /**
   * Insert an error class with converter.
   *
   * If you've inserted an duplicated error class, the closure would be
   * overwritten.
   *
   * @param creator Target error class
   * @param closure A closure function converting to the `HttpException` class
   */
  export function insert<T extends Error>(
    creator: Creator<T>,
    closure: Closure<T>,
  ): void {
    const index: number = tuples.findIndex((tuple) => tuple[0] === creator);
    if (index !== -1) tuples.splice(index, 1);

    tuples.push([creator, closure]);
    tuples.sort(([x], [y]) => (x.prototype instanceof y ? -1 : 1));
  }

  /**
   * Erase an error class.
   *
   * @param creator Target error class
   * @returns Whether be erased or not
   */
  export function erase<T extends Error>(creator: Creator<T>): boolean {
    const index: number = tuples.findIndex((tuple) => tuple[0] === creator);
    if (index === -1) return false;

    tuples.splice(index, 1);
    return true;
  }

  export function on(closure: (error: any) => any): void {
    listeners.add(closure);
  }

  export function off(closure: (error: any) => any): void {
    listeners.delete(closure);
  }

  /**
   * Type of a closure function converting to the regular
   * {@link nest.HttpException}.
   *
   * `ExceptionManager.Closure` is a type of closure function who are converting
   * from custom error to the regular {@link nest.HttpException} instance. It
   * would be used in the {@link ExceptionManager} with {@link TypedRoute} or
   * {@link EncryptedRoute}.
   */
  export interface Closure<T extends Error> {
    /**
     * Error converter.
     *
     * Convert from custom error to the regular {@link nest.HttpException}
     * instance.
     *
     * @param exception Custom error instance
     * @returns Regular {@link nest.HttpException} instance
     */
    (exception: T): HttpException;
  }

  /** @internal */
  export const tuples: Array<[Creator<any>, Closure<any>]> = [];

  /** @internal */
  export const listeners: Set<(error: any) => any> = new Set();
}

ExceptionManager.insert(
  HttpError,
  (error) =>
    new HttpException(
      {
        path: error.path,
        message: error.message,
      },
      error.status,
    ),
);