import 'dart:async';

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

import '../../../../core/utils/date_time_utils.dart';
import '../../domain/entities/dose_entry.dart';
import '../../domain/entities/injection_site.dart';
import '../../domain/value_objects/glp1_compound.dart';
import '../controllers/medication_controller.dart';
import '../widgets/log_injection_dialog.dart';

/// GLP-1 tracking dashboard.
///
/// Renders the pharmacokinetic serum estimate, the least-recently-used
/// injection-site suggestion, an interactive logging flow, and the persisted
/// injection history. A periodic ticker keeps the decaying serum value fresh
/// while the screen is visible.
class MedicationScreen extends ConsumerStatefulWidget {
  const MedicationScreen({super.key});

  @override
  ConsumerState<MedicationScreen> createState() => _MedicationScreenState();
}

class _MedicationScreenState extends ConsumerState<MedicationScreen> {
  Timer? _serumTicker;

  @override
  void initState() {
    super.initState();
    // Serum concentration decays continuously; refresh the estimate once a
    // minute so the displayed mg value tracks the pharmacokinetic model.
    _serumTicker = Timer.periodic(
      const Duration(minutes: 1),
      (_) => ref.read(medicationControllerProvider.notifier).refreshSerumLevel(),
    );
  }

  @override
  void dispose() {
    _serumTicker?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final state = ref.watch(medicationControllerProvider);

    return Scaffold(
      appBar: AppBar(title: const Text('Medication Tracker')),
      body: Center(
        child: ConstrainedBox(
          constraints: const BoxConstraints(maxWidth: 720),
          child: _buildBody(context, state),
        ),
      ),
    );
  }

  Widget _buildBody(BuildContext context, MedicationState state) {
    if (state.isLoading && state.entries.isEmpty) {
      return const Center(child: CircularProgressIndicator());
    }

    if (state.error != null && state.entries.isEmpty) {
      return _ErrorView(
        error: state.error!,
        onRetry: () =>
            ref.read(medicationControllerProvider.notifier).retry(),
      );
    }

    return ListView(
      padding: const EdgeInsets.all(16),
      children: [
        _SerumLevelCard(state: state),
        const SizedBox(height: 16),
        _SiteRotationCard(state: state),
        const SizedBox(height: 16),
        if (state.error != null) ...[
          _InlineErrorBanner(error: state.error!),
          const SizedBox(height: 16),
        ],
        FilledButton.icon(
          onPressed: () => _logInjection(state),
          icon: const Icon(Icons.add_circle_outline),
          label: const Text('Log Injection'),
        ),
        const SizedBox(height: 24),
        if (state.entries.isNotEmpty) ...[
          Text(
            'Recent Injections',
            style: Theme.of(context)
                .textTheme
                .titleMedium
                ?.copyWith(fontWeight: FontWeight.bold),
          ),
          const SizedBox(height: 8),
          for (final entry in state.entries.take(20)) _HistoryTile(entry: entry),
        ] else
          const Card(
            child: Padding(
              padding: EdgeInsets.all(16),
              child: Text(
                'No injections logged yet. Tap "Log Injection" to start '
                'tracking your doses and site rotation.',
              ),
            ),
          ),
      ],
    );
  }

  /// Opens the logging dialog pre-filled with the rotation suggestion and the
  /// latest compound, then surfaces the outcome.
  Future<void> _logInjection(MedicationState state) async {
    final result = await showLogInjectionDialog(
      context,
      initialCompound: Glp1Compound.tryParse(state.latestDose?.compoundName),
      initialSite: state.suggestedSite,
    );
    if (!mounted || result == null) return;

    ScaffoldMessenger.of(context)
      ..hideCurrentSnackBar()
      ..showSnackBar(
        SnackBar(
          content: Text(
            result
                ? 'Injection logged. Next reminder scheduled for your next dose.'
                : 'Could not log the injection. Please try again.',
          ),
          backgroundColor: result ? null : Theme.of(context).colorScheme.error,
        ),
      );
  }
}

/// Displays the current estimated serum concentration with the active
/// compound's half-life context and next dose due time.
class _SerumLevelCard extends StatelessWidget {
  const _SerumLevelCard({required this.state});

  final MedicationState state;

  @override
  Widget build(BuildContext context) {
    final latest = state.latestDose;
    final compound = Glp1Compound.tryParse(latest?.compoundName);

    return Card(
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              'Estimated Active Serum Level',
              style: Theme.of(context)
                  .textTheme
                  .titleMedium
                  ?.copyWith(fontWeight: FontWeight.bold),
            ),
            const SizedBox(height: 8),
            Text(
              '${state.serumLevelMg.toStringAsFixed(3)} mg',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
            const SizedBox(height: 4),
            if (compound != null)
              Text(
                '${compound.displayName} · half-life '
                '${compound.halfLifeHours.toStringAsFixed(0)} h',
              )
            else if (latest != null)
              Text(latest.compoundName)
            else
              const Text('No injections logged yet.'),
            Text('Evaluated ${formatDateTime(state.evaluatedAt)}'),
            if (state.nextDoseDueAt != null) ...[
              const SizedBox(height: 8),
              Text(
                'Next dose due ${formatDateTime(state.nextDoseDueAt!)}',
                style: const TextStyle(fontWeight: FontWeight.w600),
              ),
            ],
          ],
        ),
      ),
    );
  }
}

/// Shows the least-recently-used quadrant recommended for the next
/// injection, including how long ago that site was last used.
class _SiteRotationCard extends StatelessWidget {
  const _SiteRotationCard({required this.state});

  final MedicationState state;

  @override
  Widget build(BuildContext context) {
    final site = state.suggestedSite;
    final lastUsed = state.lastUsedAt(site);

    return Card(
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              'Suggested Next Injection Site',
              style: Theme.of(context)
                  .textTheme
                  .titleMedium
                  ?.copyWith(fontWeight: FontWeight.bold),
            ),
            const SizedBox(height: 8),
            ListTile(
              contentPadding: EdgeInsets.zero,
              leading: const Icon(Icons.my_location, color: Colors.teal),
              title: Text(site.displayName),
              subtitle: Text(
                '${site.region.displayName} · '
                '${lastUsed == null ? 'never used' : 'last used ${formatRelativeTime(lastUsed)}'}',
              ),
            ),
          ],
        ),
      ),
    );
  }
}

/// A single persisted injection row with an optional delete action.
class _HistoryTile extends ConsumerWidget {
  const _HistoryTile({required this.entry});

  final DoseEntry entry;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return ListTile(
      leading: Icon(_regionIcon(entry.injectionSite?.region)),
      title: Text(
        '${entry.compoundName} · ${entry.doseMg.toStringAsFixed(2)} mg',
      ),
      subtitle: Text(
        '${formatDateTime(entry.administeredAt)} · '
        '${entry.injectionSite?.displayName ?? 'Site not recorded'}',
      ),
      trailing: entry.id == null
          ? null
          : PopupMenuButton<String>(
              onSelected: (value) {
                if (value == 'delete') _confirmDelete(context, ref);
              },
              itemBuilder: (context) => const [
                PopupMenuItem(value: 'delete', child: Text('Delete')),
              ],
            ),
    );
  }

  Future<void> _confirmDelete(BuildContext context, WidgetRef ref) async {
    final confirmed = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('Delete injection?'),
        content: Text(
          '${entry.compoundName} · ${formatDateTime(entry.administeredAt)}',
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: const Text('Cancel'),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: const Text('Delete'),
          ),
        ],
      ),
    );
    if (confirmed != true) return;

    await ref
        .read(medicationControllerProvider.notifier)
        .deleteInjection(entry.id!);
  }

  IconData _regionIcon(InjectionBodyRegion? region) {
    switch (region) {
      case InjectionBodyRegion.abdomen:
        return Icons.album;
      case InjectionBodyRegion.thigh:
        return Icons.directions_walk;
      case InjectionBodyRegion.upperArm:
        return Icons.accessibility_new;
      case null:
        return Icons.help_outline;
    }
  }
}

/// Full-screen failure state shown when no history could be loaded at all.
class _ErrorView extends StatelessWidget {
  const _ErrorView({required this.error, required this.onRetry});

  final Object error;
  final VoidCallback onRetry;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(24),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Icon(Icons.error_outline, size: 48, color: Colors.red),
            const SizedBox(height: 12),
            Text(
              'Could not load your injection history.',
              style: Theme.of(context).textTheme.titleMedium,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 4),
            Text('$error', textAlign: TextAlign.center),
            const SizedBox(height: 16),
            FilledButton.icon(
              onPressed: onRetry,
              icon: const Icon(Icons.refresh),
              label: const Text('Retry'),
            ),
          ],
        ),
      ),
    );
  }
}

/// Non-blocking warning shown when a write failed while history is visible.
class _InlineErrorBanner extends StatelessWidget {
  const _InlineErrorBanner({required this.error});

  final Object error;

  @override
  Widget build(BuildContext context) {
    return Card(
      color: Theme.of(context).colorScheme.errorContainer,
      child: Padding(
        padding: const EdgeInsets.all(12),
        child: Row(
          children: [
            const Icon(Icons.warning_amber_rounded),
            const SizedBox(width: 8),
            Expanded(child: Text('$error')),
          ],
        ),
      ),
    );
  }
}