github-api.service.ts

import { Injectable } from '@angular/core';
import { HttpClient, HttpParams } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/throw';

export interface User {
  login: string;
}

export interface Issue {}

export interface SearchResults<T> {
  items: T[];
}

@Injectable()
export class GithubApiService {
  readonly API_URL = 'https://api.github.com';
  readonly WHAT = ['repositories', 'commits', 'code', 'issues', 'users'];

  constructor(private http: HttpClient) { }

  getUsers() {
    return this.http.get<User[]>(`${this.API_URL}/users`);
  }

  search<T>(what: string, params: HttpParams): Observable<SearchResults<T>> {
    if (this.WHAT.indexOf(what) === -1) {
      return Observable.throw(`Searching for ${what} is not supported. The available types are: ${this.WHAT.join(', ')}.`);
    }
    return this.http.get<SearchResults<T>>(`${this.API_URL}/search/${what}`, { params });
  }

}