Added the search functionality to the main screen

lib/src/blocs/home_bloc.dart

@@ -25,10 +25,14 @@ class HomeBloc {
   /// A subject of list of task model.
   final _tasks = BehaviorSubject<List<TaskModel>>();
 
+  /// Current text from the search box.
+  String _searchBoxText = '';
+
   // Stream getters.
   /// An observalbe of the taks of a user.
-  Observable<List<TaskModel>> get userTasks =>
-      _tasks.stream.transform(prioritySortTransformer());
+  Observable<List<TaskModel>> get userTasks => _tasks.stream
+      .transform(prioritySortTransformer())
+      .transform(searchBoxTransformer());
 
   /// An observable of the current logged in user.
   Observable<FirebaseUser> get userStream => _auth.userStream;
@@ -43,6 +47,32 @@ class HomeBloc {
     });
   }
 
+  /// Returns a stream transformer that filters the task with the text from
+  /// the search box.
+  StreamTransformer<List<TaskModel>, List<TaskModel>> searchBoxTransformer() {
+    return StreamTransformer.fromHandlers(
+      handleData: (taskList, sink) {
+        sink.add(
+          taskList.where(
+            (TaskModel task) {
+              if (_searchBoxText == '') {
+                return true;
+              }
+              // Return true if the text in the search box matches the title
+              // or the text of the task.
+              return task.event
+                      .toLowerCase()
+                      .contains(_searchBoxText.toLowerCase()) ||
+                  task.text
+                      .toLowerCase()
+                      .contains(_searchBoxText.toLowerCase());
+            },
+          ).toList(),
+        );
+      },
+    );
+  }
+
   /// Fetches the tasks for the current user.
   Future<void> fetchTasks() async {
     final user = await _auth.currentUser;
@@ -74,6 +104,11 @@ class HomeBloc {
     _taskService.setTask(task);
   }
 
+  /// Updates the serach box text.
+  void updateSearchBoxText(String newText) {
+    _searchBoxText = newText;
+  }
+
   void dispose() {
     _tasks.close();
   }

lib/src/screens/home_screen.dart

@@ -68,6 +68,7 @@ class _HomeScreenState extends State<HomeScreen> {
                     color: Theme.of(context).cardColor,
                   ),
                   SearchBox(
+                    onChanged: bloc.updateSearchBoxText,
                     height: 50.0,
                   ),
                 ],

lib/src/widgets/search-box.dart

@@ -10,7 +10,13 @@ class SearchBox extends StatelessWidget {
   /// Height of the sarch box.
   final double height;
 
-  SearchBox({@required this.height}) : assert(height >= 50);
+  /// Function to be called when the text changes.
+  final Function(String) onChanged;
+
+  SearchBox({
+    @required this.height,
+    @required this.onChanged,
+  }) : assert(height >= 50);
 
   Widget build(BuildContext context) {
     return Row(
@@ -41,6 +47,7 @@ class SearchBox extends StatelessWidget {
                 ),
                 Expanded(
                   child: TextField(
+                    onChanged: onChanged,
                     decoration: InputDecoration(
                       border: InputBorder.none,
                       hintText: 'Search...',