import { Inject, Injectable, InjectionToken } from '@angular/core';
import { UrlNormalizer } from './url-normalizer';
import { ApiMapper } from './api-mapper';


/**
 * Prefix for the URL. Can be base-relative, host-relative or absolute.
 * Always should end with slash '/'.
 */
export const APP_API_PREFIX = new InjectionToken<string>('APP_API_PREFIX');


/**
 * It maps view URLs to API and vice versa.
 */
@Injectable()
export class SingleApiMapper extends ApiMapper {

  /**
   * API URL prefix. It's absolute URL, includes base href (if applicable).
   */
  readonly prefix: string;
  private readonly endsWithSlash: boolean;

  constructor(private readonly urlNormalizer: UrlNormalizer,
              @Inject(APP_API_PREFIX) prefix: string) {
    super();

    // Normalize prefix
    this.prefix = urlNormalizer.normalize(prefix);
    this.endsWithSlash = this.prefix.endsWith('/');
  }

  mapViewToApi(path: string): string {
    // This is for diagnostics only, but might be useful
    if (/^\w+:/.test(path)) {
      throw new Error('path must be relative');
    }

    // Strip leading slash
    path = path.replace(/^\//, '');

    // Join
    // Note: API prefix MUST end with a slash, otherwise it will work as configured, which is most likely wrong.
    return (this.prefix + path).replace(/\/$/, '');
  }

  mapApiToView(url: string): string | null {
    // Normalize relative URLs
    if (url[0] === '/') {
      url = this.urlNormalizer.normalize(url);
    }

    // Remove prefix
    if (url.startsWith(this.prefix)) {
      // Strip prefix, prepend /, remove trailing /
      return '/' + url.substring(this.prefix.length).replace(/\/$/, '');
    } else if (this.endsWithSlash && url.length + 1 === this.prefix.length && this.prefix.startsWith(url)) {
      // Home
      // Note: url is missing trailing slash, but otherwise is equal to prefix
      // Example: prefix='http://.../v1/', url='http://.../v1'
      return '/';
    }

    // Unable to map
    return null;
  }
}