import {Injectable} from 'angular2/di';
import {isBlank, isPresent, BaseException, stringify} from 'angular2/src/facade/lang';
import {Map, MapWrapper, StringMapWrapper, StringMap} from 'angular2/src/facade/collection';
import {PromiseWrapper, Promise} from 'angular2/src/facade/async';
import {DOM} from 'angular2/src/dom/dom_adapter';

import {XHR} from 'angular2/src/render/xhr';

import {ViewDefinition} from '../../api';
import {UrlResolver} from 'angular2/src/services/url_resolver';

/**
 * Strategy to load component templates.
 * TODO: Make public API once we are more confident in this approach.
 */
@Injectable()
export class TemplateLoader {
  _htmlCache: StringMap<string, /*element*/ any> = StringMapWrapper.create();

  constructor(public _xhr: XHR, urlResolver: UrlResolver) {}

  load(template: ViewDefinition): Promise</*element*/ any> {
    if (isPresent(template.template)) {
      return PromiseWrapper.resolve(DOM.createTemplate(template.template));
    }
    var url = template.absUrl;
    if (isPresent(url)) {
      var promise = StringMapWrapper.get(this._htmlCache, url);

      if (isBlank(promise)) {
        // TODO(vicb): change error when TS gets fixed
        // https://github.com/angular/angular/issues/2280
        // throw new BaseException(`Failed to fetch url "${url}"`);
        promise = PromiseWrapper.then(this._xhr.get(url), html => {
          var template = DOM.createTemplate(html);
          return template;
        }, _ => PromiseWrapper.reject(new BaseException(`Failed to fetch url "${url}"`), null));

        StringMapWrapper.set(this._htmlCache, url, promise);
      }

      // We need to clone the result as others might change it
      // (e.g. the compiler).
      return promise.then((tplElement) => DOM.clone(tplElement));
    }

    throw new BaseException('View should have either the url or template property set');
  }
}