import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import 'rxjs/Rx';
import { Http } from '@angular/http';
import { environment } from '../../environments/environment';

/**
 * Service for fetching weather forecast data from Openweathermap API
 */
@Injectable()
export class WeatherService {
  /**
   * Creates an instance of WeatherService.
   * @param {Http} http HttpModule
   */
  constructor(private http: Http) {}

  /**
   * Call openweathermap api
   *
   * @returns {Observable<any[]>} the http promise
   */
  getWeatherForecast(): Observable<any[]> {
    return this.http
      .get(
        environment.baseUrl +
          '?id=' +
          environment.cityId +
          '&appid=' +
          environment.appId +
          '&units=metric'
      )
      .map(response => this.extractData(response))
      .catch(this.handleError);
  }

  /**
   * Callback function for catching AJAX call error
   *
   * @param {any} error error object
   * @returns throws error message
   */
  private handleError(error: any) {
    let errMsg: string;
    errMsg = error.message ? error.message : error.toString();
    return Observable.throw(errMsg);
  }

  /**
   * Group openweathermap api response to date
   *
   * @param {any} arr array to group
   * @param {string} key key to group
   * @returns {any} datewise grouped array
   */
  private groupBy(arr: any, key: string) {
    return arr.reduce((rv, x) => {
      const cDate = new Date(x[key] * 1000);
      const monthFormat = `${cDate.getMonth() +
        1}/${cDate.getDate()}/${cDate.getFullYear()}`;
      (rv[monthFormat] = rv[monthFormat] || []).push(x);
      return rv;
    }, {});
  }

  /**
   * Extract 5 days weatherforecast grouped by date
   *
   * @param {any} res openweathermap api response object
   * @returns {any} grouped forecast array for 5 days
   */
  private extractData(res: any): any {
    let body = res.json();
    body = body.list || {};
    body = this.groupBy(body, 'dt');
    body = Object.values(body);
    return body.slice(0, 5);
  }
}