feat: add CalendarNotifier and calendarProvider

lib/providers/calendar_provider.dart

@@ -0,0 +1,151 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../data/models/calendar_event.dart';
+import 'api_client_provider.dart';
+
+// ─── CalendarState ────────────────────────────────────────────────────────────
+
+class CalendarState {
+  final Map<DateTime, List<CalendarEvent>> eventsByDay;
+  final DateTime selectedDay;
+  final DateTime focusedMonth;
+  final DateTimeRange loadedRange;
+
+  const CalendarState({
+    required this.eventsByDay,
+    required this.selectedDay,
+    required this.focusedMonth,
+    required this.loadedRange,
+  });
+
+  CalendarState copyWith({
+    Map<DateTime, List<CalendarEvent>>? eventsByDay,
+    DateTime? selectedDay,
+    DateTime? focusedMonth,
+    DateTimeRange? loadedRange,
+  }) {
+    return CalendarState(
+      eventsByDay: eventsByDay ?? this.eventsByDay,
+      selectedDay: selectedDay ?? this.selectedDay,
+      focusedMonth: focusedMonth ?? this.focusedMonth,
+      loadedRange: loadedRange ?? this.loadedRange,
+    );
+  }
+}
+
+// ─── CalendarNotifier ─────────────────────────────────────────────────────────
+
+final calendarProvider =
+    AsyncNotifierProvider<CalendarNotifier, CalendarState>(CalendarNotifier.new);
+
+class CalendarNotifier extends AsyncNotifier<CalendarState> {
+  @override
+  Future<CalendarState> build() async {
+    final now = DateTime.now();
+    final today = dateOnly(now);
+    // Fetch current month ± 1 month as the initial window.
+    final from = DateTime(now.year, now.month - 1, 1);
+    final to = DateTime(now.year, now.month + 2, 0, 23, 59, 59);
+    final events = await ref.watch(eventsApiProvider).getEvents(from, to);
+    return CalendarState(
+      eventsByDay: _groupByDay(events),
+      selectedDay: today,
+      focusedMonth: DateTime(now.year, now.month),
+      loadedRange: DateTimeRange(start: from, end: to),
+    );
+  }
+
+  /// Synchronously updates selectedDay and focusedMonth. No API call.
+  void selectDay(DateTime day) {
+    final current = state.value;
+    if (current == null) return;
+    state = AsyncData(current.copyWith(
+      selectedDay: dateOnly(day),
+      focusedMonth: DateTime(day.year, day.month),
+    ));
+  }
+
+  /// Updates focusedMonth. Fetches events for [month] if not already loaded.
+  Future<void> loadMonth(DateTime month) async {
+    final current = state.value;
+    if (current == null) return;
+    final focused = DateTime(month.year, month.month);
+    // Always update focusedMonth so TableCalendar shows the right page.
+    state = AsyncData(current.copyWith(focusedMonth: focused));
+    // Skip fetch if the first day of [month] is within the already-loaded range.
+    final monthStart = DateTime(month.year, month.month, 1);
+    if (!monthStart.isBefore(current.loadedRange.start) &&
+        !monthStart.isAfter(current.loadedRange.end)) {
+      return;
+    }
+    try {
+      final from = DateTime(month.year, month.month, 1);
+      final to = DateTime(month.year, month.month + 1, 0, 23, 59, 59);
+      final events = await ref.read(eventsApiProvider).getEvents(from, to);
+      final s = state.value!;
+      final merged = Map<DateTime, List<CalendarEvent>>.from(s.eventsByDay);
+      for (final e in events) {
+        final key = dateOnly(e.startDt);
+        (merged[key] ??= []).add(e);
+      }
+      final newStart =
+          from.isBefore(s.loadedRange.start) ? from : s.loadedRange.start;
+      final newEnd =
+          to.isAfter(s.loadedRange.end) ? to : s.loadedRange.end;
+      state = AsyncData(s.copyWith(
+        eventsByDay: merged,
+        loadedRange: DateTimeRange(start: newStart, end: newEnd),
+      ));
+    } catch (_) {
+      // Failures are silent — already-loaded months remain visible.
+    }
+  }
+
+  /// Inserts [event] into eventsByDay after a successful createEvent API call.
+  void addEvent(CalendarEvent event) {
+    final current = state.value;
+    if (current == null) return;
+    final key = dateOnly(event.startDt);
+    final updated =
+        Map<DateTime, List<CalendarEvent>>.from(current.eventsByDay);
+    (updated[key] ??= []).add(event);
+    state = AsyncData(current.copyWith(eventsByDay: updated));
+  }
+
+  /// Replaces the old entry for [updated.id] with [updated] after a successful
+  /// updateEvent API call. Scans all buckets to handle date changes.
+  void updateEvent(CalendarEvent updated) {
+    final current = state.value;
+    if (current == null) return;
+    final byDay =
+        Map<DateTime, List<CalendarEvent>>.from(current.eventsByDay);
+    for (final key in byDay.keys) {
+      byDay[key] = byDay[key]!.where((e) => e.id != updated.id).toList();
+    }
+    final newKey = dateOnly(updated.startDt);
+    (byDay[newKey] ??= []).add(updated);
+    state = AsyncData(current.copyWith(eventsByDay: byDay));
+  }
+
+  /// Removes event [id] from [date]'s bucket after a successful deleteEvent
+  /// API call.
+  void removeEvent(int id, DateTime date) {
+    final current = state.value;
+    if (current == null) return;
+    final key = dateOnly(date);
+    final byDay =
+        Map<DateTime, List<CalendarEvent>>.from(current.eventsByDay);
+    byDay[key] = (byDay[key] ?? []).where((e) => e.id != id).toList();
+    state = AsyncData(current.copyWith(eventsByDay: byDay));
+  }
+}
+
+Map<DateTime, List<CalendarEvent>> _groupByDay(List<CalendarEvent> events) {
+  final byDay = <DateTime, List<CalendarEvent>>{};
+  for (final e in events) {
+    final key = dateOnly(e.startDt);
+    (byDay[key] ??= []).add(e);
+  }
+  return byDay;
+}