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

import '../../../../core/database/app_database.dart';
import '../../../../core/platform/health_gateway.dart';
import '../../../../core/utils/date_time_utils.dart';
import '../../data/repositories/health_sync_repository.dart';
import '../../domain/entities/biometric_entry.dart';
import '../../domain/repositories/health_sync_repository.dart';

/// Application-wide biometric repository (drift-backed).
///
/// Overridable in widget/unit tests with an in-memory fake.
final healthSyncRepositoryProvider = Provider<IHealthSyncRepository>(
  (ref) => HealthSyncRepository(ref.watch(appDatabaseProvider)),
);

/// Cross-platform health boundary (HealthKit / Health Connect on mobile,
/// manual-entry fallback on Web/Windows/macOS).
///
/// Overridable in tests with a fake gateway.
final healthGatewayProvider = Provider<IHealthGateway>(
  (ref) => createHealthGateway(),
);

/// Immutable snapshot of the weight/biometric tracking state.
class BiometricState {
  const BiometricState({
    required this.history,
    required this.evaluatedAt,
    this.isSyncing = false,
    this.statusMessage,
    this.error,
  });

  /// Full biometric history, newest first.
  final List<BiometricEntry> history;

  /// Timestamp at which the trend deltas were evaluated.
  final DateTime evaluatedAt;

  /// Whether a native health sync is currently in flight.
  final bool isSyncing;

  /// Human-readable outcome of the last sync/manual action (snackbar text).
  final String? statusMessage;

  /// Most recent persistence/gateway failure, cleared on the next success.
  final Object? error;

  /// Most recent biometric sample, or `null` on an empty history.
  BiometricEntry? get latest => history.isEmpty ? null : history.first;

  /// Most recent recorded weight, or `null` on an empty history.
  double? get latestWeightLbs => latest?.weightLbs;

  /// Most recent active-energy sample (kcal), or `null` when none exists.
  double? get latestActiveCaloriesBurned {
    for (final entry in history) {
      final calories = entry.activeCaloriesBurned;
      if (calories != null) return calories;
    }
    return null;
  }

  /// Weight change (lbs) between the newest sample and the most recent
  /// sample at least [days] old; `null` when the history does not reach back
  /// that far. Negative values mean weight loss.
  double? weightDeltaOver(int days, {DateTime? now}) {
    final newest = latestWeightLbs;
    if (newest == null) return null;

    final cutoff = (now ?? evaluatedAt).subtract(Duration(days: days));
    double? baseline;
    for (final entry in history) {
      if (!entry.timestamp.isAfter(cutoff)) {
        // Newest-first ordering: the first entry at/before the cutoff is the
        // closest baseline to it.
        baseline = entry.weightLbs;
        break;
      }
    }
    if (baseline == null) return null;
    return newest - baseline;
  }

  /// Weight change over the trailing 7 days.
  double? get weight7DayDelta => weightDeltaOver(7);

  /// Weight change over the trailing 30 days.
  double? get weight30DayDelta => weightDeltaOver(30);

  BiometricState copyWith({
    List<BiometricEntry>? history,
    DateTime? evaluatedAt,
    bool? isSyncing,
    String? statusMessage,
    Object? error,
    bool clearError = false,
    bool clearStatus = false,
  }) =>
      BiometricState(
        history: history ?? this.history,
        evaluatedAt: evaluatedAt ?? this.evaluatedAt,
        isSyncing: isSyncing ?? this.isSyncing,
        statusMessage: clearStatus ? null : statusMessage ?? this.statusMessage,
        error: clearError ? null : error ?? this.error,
      );
}

/// Orchestrates the health-sync feature: persists manual biometric entries,
/// derives 7/30-day weight trends, and imports weight + active-energy data
/// through the platform [IHealthGateway] (HealthKit / Health Connect) with a
/// graceful manual-entry fallback on Web/Windows/macOS.
class BiometricController extends AsyncNotifier<BiometricState> {
  /// How far back a native sync imports samples.
  static const Duration syncWindow = Duration(days: 90);

  /// Maximum number of history rows kept in the presentation state.
  static const int historyLimit = 365;

  @override
  Future<BiometricState> build() => _load();

  /// Persists a manually entered weight sample and refreshes trends.
  Future<bool> logWeight({
    required double weightLbs,
    DateTime? timestamp,
  }) async {
    if (weightLbs <= 0) return false;

    try {
      final saved = await ref.read(healthSyncRepositoryProvider).saveBiometric(
            BiometricEntry(
              timestamp: timestamp ?? DateTime.now(),
              weightLbs: weightLbs,
              source: BiometricSource.manual,
            ),
          );
      await _refresh(
        statusMessage: 'Logged ${saved.weightLbs.toStringAsFixed(1)} lb',
      );
      return true;
    } catch (error, stackTrace) {
      _recordError(error, stackTrace, 'saveBiometric failed');
      return false;
    }
  }

  /// Removes a biometric sample by database [id].
  Future<bool> deleteEntry(int id) async {
    try {
      await ref.read(healthSyncRepositoryProvider).deleteBiometric(id);
      await _refresh();
      return true;
    } catch (error, stackTrace) {
      _recordError(error, stackTrace, 'deleteBiometric failed');
      return false;
    }
  }

  /// Imports weight and active-energy samples from the native health store
  /// over the trailing [window] and persists them idempotently (the previous
  /// import for the same source/window is replaced, not duplicated).
  ///
  /// Returns `false` when the platform is unsupported (Web/Windows/macOS —
  /// callers should open the manual-entry dialog instead), when permission
  /// is denied, or when the sync throws; the reason is reflected in
  /// [BiometricState.statusMessage].
  Future<bool> syncFromHealth({Duration window = syncWindow}) async {
    final gateway = ref.read(healthGatewayProvider);
    if (!gateway.supportsNativeHealth) {
      await _refresh(
        statusMessage:
            'Native health sync is unavailable here - use manual entry.',
      );
      return false;
    }

    _setState(
      AsyncData(
        state.valueOrNull?.copyWith(isSyncing: true) ??
            BiometricState(
              history: const [],
              evaluatedAt: DateTime.now(),
              isSyncing: true,
            ),
      ),
    );

    try {
      final granted = await gateway.requestPermissions();
      if (!granted) {
        await _refresh(
          statusMessage: 'Health permissions were denied.',
          error: StateError('Health permissions denied'),
        );
        return false;
      }

      final now = DateTime.now();
      final start = now.subtract(window);
      final weights = await gateway.fetchWeightHistory(start: start, end: now);
      final energies =
          await gateway.fetchActiveEnergyBurned(start: start, end: now);

      final source = switch (gateway.nativePlatform) {
        NativeHealthPlatform.appleHealth => BiometricSource.appleHealth,
        NativeHealthPlatform.healthConnect => BiometricSource.healthConnect,
        null => BiometricSource.cloudSync,
      };

      final repository = ref.read(healthSyncRepositoryProvider);
      // Idempotent re-sync: drop the previous import for this source/window.
      await repository.clearSyncedRange(
        source: source,
        start: start,
        end: now,
      );

      final savedWeights = <BiometricEntry>[];
      for (final metric in weights) {
        savedWeights.add(
          await repository.saveBiometric(
            BiometricEntry(
              timestamp: metric.timestamp,
              weightLbs: metric.value,
              source: source,
            ),
          ),
        );
      }

      final energyDays = _groupEnergyByDay(energies);
      var energyDaysStored = 0;
      for (final day in energyDays.entries) {
        final entry = _buildEnergyEntry(
          dayStart: day.key,
          kcal: day.value,
          energies: energies,
          savedWeights: savedWeights,
          fallbackHistory: state.valueOrNull?.history ?? const [],
          source: source,
        );
        if (entry == null) continue;
        await repository.saveBiometric(entry);
        energyDaysStored++;
      }

      await _refresh(
        statusMessage: 'Synced ${weights.length} weight sample(s), '
            '$energyDaysStored day(s) of active energy.',
      );
      return true;
    } catch (error, stackTrace) {
      _recordError(error, stackTrace, 'syncFromHealth failed');
      return false;
    }
  }

  /// Reloads the snapshot after a failed build (error-state retry action).
  Future<void> retry() async {
    _setState(const AsyncLoading());
    try {
      _setState(AsyncData(await _load()));
    } catch (error, stackTrace) {
      _setState(AsyncError(error, stackTrace));
    }
  }

  /// Reloads the biometric history from the repository.
  Future<BiometricState> _load({String? statusMessage, Object? error}) async {
    final history = await ref
        .read(healthSyncRepositoryProvider)
        .getBiometrics(limit: historyLimit);
    return BiometricState(
      history: history,
      evaluatedAt: DateTime.now(),
      statusMessage: statusMessage,
      error: error,
    );
  }

  /// Replaces the current state with a fresh snapshot; failures keep the
  /// previous data so the UI never flashes empty after a rejected write.
  Future<void> _refresh({String? statusMessage, Object? error}) async {
    try {
      _setState(AsyncData(
        await _load(statusMessage: statusMessage, error: error),
      ));
    } catch (loadError, stackTrace) {
      _recordError(loadError, stackTrace, 'biometric snapshot refresh failed');
    }
  }

  /// Attaches a non-destructive error to the last known good state (or as an
  /// [AsyncError] when nothing has loaded yet).
  void _recordError(Object error, StackTrace stackTrace, String label) {
    debugPrintStack(stackTrace: stackTrace, label: '$label failed');
    final current = state.valueOrNull;
    if (current == null) {
      _setState(AsyncError(error, stackTrace));
    } else {
      _setState(AsyncData(current.copyWith(error: error)));
    }
  }

  void _setState(AsyncValue<BiometricState> next) => state = next;

  /// Sums active-energy samples per local calendar day (day-start anchors),
  /// returned in chronological order.
  Map<DateTime, double> _groupEnergyByDay(List<HealthMetric> energies) {
    final perDay = <DateTime, double>{};
    for (final metric in energies) {
      final day = startOfDay(metric.timestamp);
      perDay[day] = (perDay[day] ?? 0) + metric.value;
    }
    final entries = perDay.entries.toList()
      ..sort((a, b) => a.key.compareTo(b.key));
    return Map.fromEntries(entries);
  }

  /// Builds the entry carrying [kcal] for one day: attaches the total to
  /// that day's synced weight sample when one exists, otherwise creates a
  /// standalone sample anchored to the day's last energy reading using the
  /// nearest prior known weight. Returns `null` when no weight is known yet.
  BiometricEntry? _buildEnergyEntry({
    required DateTime dayStart,
    required double kcal,
    required List<HealthMetric> energies,
    required List<BiometricEntry> savedWeights,
    required List<BiometricEntry> fallbackHistory,
    required BiometricSource source,
  }) {
    // Weight recorded on the same day (lists are newest-first).
    BiometricEntry? sameDay;
    for (final weight in savedWeights) {
      if (startOfDay(weight.timestamp) == dayStart) {
        sameDay ??= weight;
      }
    }
    if (sameDay != null) {
      return sameDay.copyWith(activeCaloriesBurned: kcal);
    }

    // Nearest prior weight within the synced window.
    final dayEnd = endOfDay(dayStart);
    BiometricEntry? prior;
    for (final weight in savedWeights) {
      if (weight.timestamp.isBefore(dayEnd) &&
          (prior == null || weight.timestamp.isAfter(prior.timestamp))) {
        prior = weight;
      }
    }
    // Fall back to the cached local history (entries older than the window).
    if (prior == null) {
      for (final entry in fallbackHistory) {
        if (entry.timestamp.isBefore(dayEnd) &&
            (prior == null || entry.timestamp.isAfter(prior.timestamp))) {
          prior = entry;
        }
      }
    }
    if (prior == null) return null;

    // Anchor the sample to the day's last energy reading inside the window.
    DateTime? anchor;
    for (final metric in energies) {
      if (startOfDay(metric.timestamp) == dayStart &&
          (anchor == null || metric.timestamp.isAfter(anchor))) {
        anchor = metric.timestamp;
      }
    }

    return BiometricEntry(
      timestamp: anchor ?? dayStart,
      weightLbs: prior.weightLbs,
      activeCaloriesBurned: kcal,
      source: source,
    );
  }
}

/// Exposes the [BiometricController] to the widget tree.
final biometricControllerProvider =
    AsyncNotifierProvider<BiometricController, BiometricState>(
  BiometricController.new,
);