# Architecture Decision Records — Task & Habit Tracker

## ADR-001: State Management
**Date:** 2026-08-08  **Status:** Accepted

**Context:** The app has complex async state (network + local DB), needs dependency injection, and will be maintained long-term.

**Options:**
- Provider: Simple, official, but lacks code gen and async patterns
- BLoC: Battle-tested, verbose, steep learning curve
- Riverpod 2.x: Modern, code generation, excellent async support, testable

**Decision:** Riverpod 2.x with code generation (@riverpod annotation)

**Consequences:**
+ Excellent separation of concerns
+ Compile-time safety with code gen
+ Easy to test with provider overrides
- Requires `build_runner` in workflow
- Team must learn Riverpod-specific patterns

---

## ADR-002: Backend / Persistence
**Date:** 2026-08-08  **Status:** Accepted

**Context:** Need auth, real-time sync, and offline-first capability.

**Options:**
- Firebase: Excellent offline support, real-time, proprietary lock-in
- Supabase: Open source, PostgreSQL, REST + realtime
- Custom REST: Full control, requires backend team

**Decision:** Supabase for backend + Drift (SQLite) for local persistence

**Consequences:**
+ Open source, can self-host
+ Drift provides type-safe SQL with code gen
+ Offline-first: write to Drift, sync to Supabase on connectivity
- Two data layers to maintain
- Conflict resolution needed for sync

---

## ADR-003: Local Persistence
**Decision:** Drift (SQLite wrapper)

**Why not Hive:** Hive is a key-value store — no relational queries. Can't efficiently query "all habits due today".
**Why not SharedPreferences:** Only for simple key-value settings (theme, onboarding status).
**Why Drift:** Type-safe, reactive (returns Streams), supports complex SQL queries, integrates with Riverpod's AsyncNotifier.

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// ─── Domain Models ─────────────────────────────────────────────
class Task {
  final String id, title, description;
  final bool completed;
  final DateTime dueDate;
  Task({required this.id, required this.title, this.description = '', this.completed = false, required this.dueDate});
  Task copyWith({bool? completed}) => Task(id: id, title: title, description: description, completed: completed ?? this.completed, dueDate: dueDate);
}

class Habit {
  final String id, name, emoji;
  final List completedDates;
  Habit({required this.id, required this.name, required this.emoji, this.completedDates = const []});
  int get streak {
    int s = 0;
    var d = DateTime.now();
    for (int i = 0; i < 365; i++) {
      final check = DateTime(d.year, d.month, d.day - i);
      if (completedDates.any((c) => c.year == check.year && c.month == check.month && c.day == check.day)) s++;
      else break;
    }
    return s;
  }
}

// ─── Fake Repository (swap for real in Stage 4) ────────────────
class TaskRepository {
  final List _tasks = [
    Task(id: '1', title: 'Review pull request', description: 'Review Tarun\'s PR #42', dueDate: DateTime.now()),
    Task(id: '2', title: 'Write unit tests', description: 'Cover the auth service', completed: true, dueDate: DateTime.now()),
    Task(id: '3', title: 'Deploy to staging', dueDate: DateTime.now()),
  ];
  List getToday() => _tasks.where((t) => t.dueDate.day == DateTime.now().day).toList();
  void toggle(String id) {
    final i = _tasks.indexWhere((t) => t.id == id);
    if (i != -1) _tasks[i] = _tasks[i].copyWith(completed: !_tasks[i].completed);
  }
  void add(String title) => _tasks.add(Task(id: DateTime.now().millisecondsSinceEpoch.toString(), title: title, dueDate: DateTime.now()));
}

// ─── Riverpod Providers ────────────────────────────────────────
final taskRepoProvider = Provider((_) => TaskRepository());
final tasksProvider = StateNotifierProvider<_TasksNotifier, List>((ref) => _TasksNotifier(ref.read(taskRepoProvider)));

class _TasksNotifier extends StateNotifier> {
  final TaskRepository _repo;
  _TasksNotifier(this._repo) : super([]) { _load(); }
  void _load() => state = _repo.getToday();
  void toggle(String id) { _repo.toggle(id); _load(); }
  void add(String title) { _repo.add(title); _load(); }
}

// ─── Main App ──────────────────────────────────────────────────
void main() => runApp(const ProviderScope(child: MaterialApp(home: HomeScreen())));

class HomeScreen extends ConsumerWidget {
  const HomeScreen({super.key});
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final tasks = ref.watch(tasksProvider);
    final done = tasks.where((t) => t.completed).length;
    return Scaffold(
      appBar: AppBar(
        title: const Text('Today'),
        subtitle: Text('$done/${tasks.length} complete'),
      ),
      body: ListView.builder(
        itemCount: tasks.length,
        itemBuilder: (_, i) => ListTile(
          leading: Checkbox(value: tasks[i].completed, onChanged: (_) => ref.read(tasksProvider.notifier).toggle(tasks[i].id)),
          title: Text(tasks[i].title, style: tasks[i].completed ? const TextStyle(decoration: TextDecoration.lineThrough, color: Colors.grey) : null),
          subtitle: tasks[i].description.isNotEmpty ? Text(tasks[i].description) : null,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => showModalBottomSheet(
          context: context,
          builder: (_) => AddTaskSheet(onAdd: (title) => ref.read(tasksProvider.notifier).add(title)),
        ),
        child: const Icon(Icons.add),
      ),
    );
  }
}

class AddTaskSheet extends StatelessWidget {
  final void Function(String) onAdd;
  const AddTaskSheet({super.key, required this.onAdd});
  @override
  Widget build(BuildContext context) {
    final ctrl = TextEditingController();
    return Padding(
      padding: EdgeInsets.only(bottom: MediaQuery.viewInsetsOf(context).bottom, left: 24, right: 24, top: 24),
      child: Column(mainAxisSize: MainAxisSize.min, children: [
        TextField(controller: ctrl, autofocus: true, decoration: const InputDecoration(labelText: 'New task', border: OutlineInputBorder())),
        const SizedBox(height: 16),
        FilledButton(onPressed: () { onAdd(ctrl.text); Navigator.pop(context); }, child: const Text('Add Task')),
        const SizedBox(height: 16),
      ]),
    );
  }
}