Created the [FirestoreProvider], added the id attribute to the user, event and task models

lib/src/resources/firestore_provider.dart

@@ -0,0 +1,91 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:rxdart/rxdart.dart';
+
+import '../models/event_model.dart';
+import '../models/user_model.dart';
+import '../models/task_model.dart';
+
+/// A connection to the Cloud Firestore database
+class FirestoreProvider {
+  final Firestore firestore = Firestore.instance;
+
+  FirestoreProvider() {
+    firestore.settings(timestampsInSnapshotsEnabled: true);
+  }
+
+  /// Returns a stream of [UserModel].
+  Observable<UserModel> getUser(String username) {
+    final mappedStream = firestore
+        .collection('users')
+        .where('username', isEqualTo: username)
+        .snapshots()
+        .map(
+      (QuerySnapshot snapshot) {
+        if (snapshot.documents.isEmpty) {
+          return null;
+        }
+        final userSnapshot = snapshot.documents.first;
+        return UserModel.fromFirestore(
+            userSnapshot.data, userSnapshot.documentID);
+      },
+    );
+    return Observable(mappedStream);
+  }
+
+  /// Returns a stream of [List<Task>]
+  ///
+  /// The [event] parameter is used to query tasks that only are part of a
+  /// certain event.
+  Observable<List<TaskModel>> getUserTasks(String username, {String event}) {
+    Query query = firestore
+        .collection('tasks')
+        .where('ownerUsername', isEqualTo: username)
+        .where('done', isEqualTo: false);
+
+    if (event != null) {
+      query = query.where('event', isEqualTo: event);
+    }
+
+    final mappedStream = query.snapshots().map(
+      (QuerySnapshot snapshot) {
+        return snapshot.documents.map(
+          (DocumentSnapshot document) {
+            return TaskModel.fromFirestore(document.data, document.documentID);
+          },
+        ).toList();
+      },
+    );
+
+    return Observable(mappedStream);
+  }
+
+  Observable<TaskModel> getTask(String id) {
+    final mappedStream =
+        firestore.collection('tasks').document(id).snapshots().map(
+      (DocumentSnapshot snapshot) {
+        return TaskModel.fromFirestore(snapshot.data, snapshot.documentID);
+      },
+    );
+
+    return Observable(mappedStream);
+  }
+
+  // TODO: Change the Events collction name to 'events'
+  Observable<List<EventModel>> getUserEvents(String userDocumentId) {
+    final mappedStream = firestore
+        .collection('users')
+        .document(userDocumentId)
+        .collection('Events')
+        .snapshots()
+        .map(
+      (QuerySnapshot snapshot) {
+        return snapshot.documents.map((DocumentSnapshot documentSnapshot) {
+          return EventModel.fromFirestore(
+              documentSnapshot.data, documentSnapshot.documentID);
+        }).toList();
+      },
+    );
+
+    return Observable(mappedStream);
+  }
+}