file upload

src/app/songs/services/file-data.service.ts

@@ -0,0 +1,19 @@
+import {Injectable} from '@angular/core';
+import {SongDataService} from './song-data.service';
+import {File} from './file';
+
+@Injectable({
+  providedIn: 'root'
+})
+export class FileDataService {
+
+  constructor(private songDataService: SongDataService) {
+  }
+
+  public async put(songId: string, file: File): Promise<string> {
+    const songRef = this.songDataService.getSongRef(songId);
+    const fileCollection = songRef.collection('files');
+    const id = await fileCollection.add(file);
+    return id.id;
+  }
+}