feat: animate goal progress indicator

lib/ui/widgets/goal_progress_indicator.dart

@@ -5,20 +5,41 @@ import 'package:financial_dashboard/ui/ui.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 
-class GoalProgressIndicator extends StatelessWidget {
+class GoalProgressIndicator extends StatefulWidget {
   const GoalProgressIndicator({
     super.key,
     this.size = AppSpacing.xxxlg,
-    this.value = 0,
     this.isGradient = false,
   });
 
   final double size;
 
-  /// Value as a percentage between 0.0 and 1.0.
-  final double value;
   final bool isGradient;
 
+  @override
+  State<GoalProgressIndicator> createState() => _GoalProgressIndicatorState();
+}
+
+class _GoalProgressIndicatorState extends State<GoalProgressIndicator>
+    with TickerProviderStateMixin {
+  late AnimationController _controller;
+  late Animation<double> _animation;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      duration: const Duration(seconds: 1),
+      vsync: this,
+    );
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
@@ -35,28 +56,45 @@ class GoalProgressIndicator extends StatelessWidget {
     if (monthlySpendingLimitGoal != 0) {
       value = transactions.spent.abs() / monthlySpendingLimitGoal;
     }
-    final displayValue = (value * 100).toInt();
 
+    var begin = 0.0;
+    if (_controller.isCompleted) {
+      begin = _animation.value;
+      _controller.reset();
+    }
+
+    _animation = Tween<double>(begin: begin, end: value).animate(
+      _controller,
+    );
+
+    _controller.forward();
     return SizedBox(
-      height: size,
-      width: size,
-      child: CustomPaint(
-        painter: CircleProgressPainter(
-          colorScheme: coloScheme,
-          isGradient: isGradient,
-          value: value,
-        ),
-        child: Center(
-          child: DefaultTextStyle(
-            style: textTheme.titleMedium!,
-            textHeightBehavior: const TextHeightBehavior(
-              applyHeightToFirstAscent: false,
+      height: widget.size,
+      width: widget.size,
+      child: AnimatedBuilder(
+        animation: _animation,
+        builder: (context, child) {
+          final value = _animation.value;
+          final displayValue = (value * 100).toInt();
+          return CustomPaint(
+            painter: CircleProgressPainter(
+              colorScheme: coloScheme,
+              isGradient: widget.isGradient,
+              value: value,
             ),
-            child: Text(
-              '$displayValue%',
+            child: Center(
+              child: DefaultTextStyle(
+                style: textTheme.titleMedium!,
+                textHeightBehavior: const TextHeightBehavior(
+                  applyHeightToFirstAscent: false,
+                ),
+                child: Text(
+                  '$displayValue%',
+                ),
+              ),
             ),
-          ),
-        ),
+          );
+        },
       ),
     );
   }
@@ -133,6 +171,7 @@ class CircleProgressPainter extends CustomPainter {
   @override
   bool shouldRepaint(covariant CircleProgressPainter oldDelegate) {
     return colorScheme != oldDelegate.colorScheme ||
-        isGradient != oldDelegate.isGradient;
+        isGradient != oldDelegate.isGradient ||
+        value != oldDelegate.value;
   }
 }

test/src/ui/widgets/goal_progress_indicator_test.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:bloc_test/bloc_test.dart';
 import 'package:financial_dashboard/financial_data/financial_data.dart';
 import 'package:financial_dashboard/ui/ui.dart';
@@ -19,6 +21,59 @@ class _MockFinancialDataBloc
     implements FinancialDataBloc {}
 
 void main() {
+  group('$GoalProgressIndicator', () {
+    late FinancialDataBloc financialDataBloc;
+
+    setUp(() {
+      financialDataBloc = _MockFinancialDataBloc();
+    });
+
+    testWidgets('animates from last value if present', (tester) async {
+      final streamController = StreamController<FinancialDataState>();
+      final beginState = FinancialDataState(
+        currentSavings: 12456,
+        savingsDataPoints: createSampleData(),
+        monthlySpendingLimitGoal: 100,
+        transactions: createSampleTransactions(),
+      );
+      final endState = FinancialDataState(
+        currentSavings: 12456,
+        savingsDataPoints: createSampleData(),
+        monthlySpendingLimitGoal: 1000,
+        transactions: createSampleTransactions(),
+      );
+      whenListen(
+        financialDataBloc,
+        streamController.stream,
+        initialState: beginState,
+      );
+
+      var value = beginState.transactions.spent.abs() /
+          beginState.monthlySpendingLimitGoal;
+      var displayValue = (value * 100).toInt();
+
+      await tester.pumpExperience(
+        GoalProgressIndicator(),
+        financialDataBloc: financialDataBloc,
+      );
+
+      await tester.pumpAndSettle();
+      expect(find.text('$displayValue%'), findsOneWidget);
+
+      streamController.add(endState);
+
+      await tester.pump();
+      expect(find.text('$displayValue%'), findsOneWidget);
+
+      await tester.pumpAndSettle();
+
+      value =
+          endState.transactions.spent.abs() / endState.monthlySpendingLimitGoal;
+      displayValue = (value * 100).toInt();
+      expect(find.text('$displayValue%'), findsOneWidget);
+    });
+  });
+
   group('CircleProgressPainter', () {
     late FinancialDataBloc financialDataBloc;
 
@@ -36,7 +91,7 @@ void main() {
     group('$GoalProgressIndicator', () {
       testWidgets('renders without gradient', (tester) async {
         await tester.pumpExperience(
-          GoalProgressIndicator(value: 1),
+          GoalProgressIndicator(),
           financialDataBloc: financialDataBloc,
         );
         await tester.pumpAndSettle();