refractor: core module (#289)

* Shift services into their own folders.
* Add comments.

Fixes #288

src/app/core/progress-bar/progress-bar.service.ts

@@ -1,29 +1,48 @@
+/** Angular Imports */
 import { Injectable, EventEmitter } from '@angular/core';
 
-@Injectable({
-  providedIn: 'root'
-})
+/**
+ * Progress bar service.
+ */
+@Injectable()
 export class ProgressBarService {
 
+  /** Progress bar update event. */
   public updateProgressBar: EventEmitter<any>;
+  /** Denotes the number of requests currently running. */
   private requestsRunning = 0;
 
+  /**
+   * Initializes progress bar update event.
+   */
   constructor() {
     this.updateProgressBar = new EventEmitter();
   }
 
+  /**
+   * Returns the number of Http requests currently running.
+   * @returns {number} Number of Http requests currently running.
+   */
   public getRequestsRunning(): number {
     return this.requestsRunning;
   }
 
-  public increase(): void {
+  /**
+   * Increments the number of Http requests currently running
+   * and emits a progress bar update event `indeterminate` when the first request is run.
+   */
+  public increase() {
     this.requestsRunning++;
     if (this.requestsRunning === 1) {
       this.updateProgressBar.emit('indeterminate');
     }
   }
 
-  public decrease(): void {
+  /**
+   * Decrements the number of Http requests currently running
+   * and emits a progress bar update event `none` when no request is running.
+   */
+  public decrease() {
     if (this.requestsRunning > 0) {
       this.requestsRunning--;
       if (this.requestsRunning === 0) {

src/app/core/progress-bar/progress.interceptor.ts

@@ -1,16 +1,29 @@
+/** Angular Imports */
 import { Injectable } from '@angular/core';
 import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse} from '@angular/common/http';
 
+/** rxjs Imports */
 import { Observable } from 'rxjs';
 import { tap, catchError } from 'rxjs/operators';
 
+/** Custom Services */
 import { ProgressBarService } from './progress-bar.service';
 
+/**
+ * Http Request interceptor to start/stop loading the progress bar.
+ */
 @Injectable()
 export class ProgressInterceptor implements HttpInterceptor {
 
+  /**
+   * @param {ProgressBarService} progressBarService Progress Bar Service.
+   */
   constructor(private progressBarService: ProgressBarService) { }
 
+  /**
+   * Intercepts a Http request to start loading the progress bar for a pending request
+   * and stop when a response or error is received.
+   */
   intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
     this.progressBarService.increase();
     return next.handle(request)