import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../plants/data/plants_provider.dart';
import '../../plants/domain/plant.dart';
import '../domain/due_task.dart';

DateTime _dateOnly(DateTime dt) => DateTime(dt.year, dt.month, dt.day);

DateTime? _nextDue(DateTime? lastDone, int intervalDays, DateTime today) {
  // Noch nie erledigt → sofort fällig.
  if (lastDone == null) return today;
  return _dateOnly(lastDone).add(Duration(days: intervalDays));
}

Iterable<DueTask> _tasksForPlant(Plant plant, DateTime today) sync* {
  final watering = _nextDue(plant.lastWatered, plant.wateringIntervalDays, today);
  if (watering != null && !watering.isAfter(today)) {
    yield DueTask(plant: plant, type: CareTaskType.watering, dueDate: watering);
  }
  final fertilizing =
      _nextDue(plant.lastFertilized, plant.fertilizingIntervalDays, today);
  if (fertilizing != null && !fertilizing.isAfter(today)) {
    yield DueTask(
        plant: plant, type: CareTaskType.fertilizing, dueDate: fertilizing);
  }
}

/// Alle heute fälligen und überfälligen Aufgaben, Überfälliges zuerst.
final dueTasksProvider = Provider<List<DueTask>>((ref) {
  final plants = ref.watch(plantsProvider);
  final today = _dateOnly(DateTime.now());

  final tasks = [
    for (final plant in plants) ..._tasksForPlant(plant, today),
  ];
  tasks.sort((a, b) {
    final byDate = a.dueDate.compareTo(b.dueDate);
    if (byDate != 0) return byDate;
    return a.plant.nickname.compareTo(b.plant.nickname);
  });
  return tasks;
});

/// Das nächste zukünftige Fälligkeitsdatum – für den "Alles versorgt"-Screen
/// ("Nächste Aufgabe: Freitag").
final nextDueDateProvider = Provider<DateTime?>((ref) {
  final plants = ref.watch(plantsProvider);
  final today = _dateOnly(DateTime.now());

  DateTime? next;
  for (final plant in plants) {
    for (final candidate in [
      _nextDue(plant.lastWatered, plant.wateringIntervalDays, today),
      _nextDue(plant.lastFertilized, plant.fertilizingIntervalDays, today),
    ]) {
      if (candidate == null || !candidate.isAfter(today)) continue;
      if (next == null || candidate.isBefore(next)) next = candidate;
    }
  }
  return next;
});