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

import '../../core/constants.dart';
import '../../data/local/database.dart';
import '../../data/models/milestone.dart';
import '../../data/models/project.dart';
import '../../data/models/task.dart';
import '../../providers/api_client_provider.dart';
import '../../providers/milestones_provider.dart';
import '../../providers/projects_provider.dart';
import '../../providers/tasks_provider.dart';
import '../../widgets/pending_sync_badge.dart';

class ProjectTasksScreen extends ConsumerStatefulWidget {
  final int projectId;
  const ProjectTasksScreen({super.key, required this.projectId});

  @override
  ConsumerState<ProjectTasksScreen> createState() => _ProjectTasksScreenState();
}

class _ProjectTasksScreenState extends ConsumerState<ProjectTasksScreen> {
  // Local optimistic status overrides — avoids a reload flash on every cycle tap.
  final Map<int, TaskStatus> _pendingStatus = {};

  TaskStatus _effectiveStatus(Task task) =>
      _pendingStatus[task.id] ?? task.status;

  TaskStatus _nextStatus(TaskStatus s) => switch (s) {
        TaskStatus.todo => TaskStatus.inProgress,
        TaskStatus.inProgress => TaskStatus.done,
        TaskStatus.done => TaskStatus.todo,
      };

  Future<void> _cycleStatus(Task task) async {
    final current = _effectiveStatus(task);
    final next = _nextStatus(current);
    setState(() => _pendingStatus[task.id] = next);
    try {
      await ref
          .read(tasksRepositoryProvider)
          .update(task.id, {'status': next.value});
      // Sync the global tasks list so the library view stays consistent.
      ref.invalidate(tasksProvider);
    } catch (_) {
      // Revert optimistic change on error.
      setState(() => _pendingStatus.remove(task.id));
    }
  }

  void _openTask(int taskId) {
    context
        .push(Routes.taskEdit.replaceFirst(':id', '$taskId'))
        .then((_) => ref.invalidate(projectTasksProvider(widget.projectId)));
  }

  Color _parseColor(String? hex) {
    if (hex == null || hex.isEmpty) return const Color(0xFF5B4A8A);
    try {
      return Color(int.parse(hex.replaceFirst('#', '0xFF')));
    } catch (_) {
      return const Color(0xFF5B4A8A);
    }
  }

  @override
  Widget build(BuildContext context) {
    final tasksAsync = ref.watch(projectTasksProvider(widget.projectId));
    final milestonesAsync = ref.watch(projectMilestonesProvider(widget.projectId));
    final project = ref.watch(projectsProvider).value
        ?.whereType<Project>()
        .where((p) => p.id == widget.projectId)
        .firstOrNull;

    final color = _parseColor(project?.color);

    return Scaffold(
      appBar: AppBar(
        title: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              project?.title ?? 'Project',
              style: Theme.of(context).textTheme.titleLarge,
            ),
            if (project?.description?.isNotEmpty == true)
              Text(
                project!.description!,
                style: Theme.of(context).textTheme.labelSmall?.copyWith(
                      color: Theme.of(context).colorScheme.onSurfaceVariant,
                    ),
                maxLines: 1,
                overflow: TextOverflow.ellipsis,
              ),
          ],
        ),
        actions: [
          IconButton(
            icon: const Icon(LucideIcons.pencil),
            tooltip: 'Edit project',
            onPressed: () =>
                context.push('/projects/${widget.projectId}/edit'),
          ),
        ],
      ),
      body: tasksAsync.when(
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (e, _) => Center(child: Text('Error loading tasks: $e')),
        data: (tasks) => _buildBody(context, tasks, milestonesAsync, color),
      ),
    );
  }

  Widget _buildBody(
    BuildContext context,
    List<Task> tasks,
    AsyncValue<List<Milestone>> milestonesAsync,
    Color color,
  ) {
    final milestones = (milestonesAsync.value ?? []).toList()
      ..sort((a, b) => a.orderIndex.compareTo(b.orderIndex));

    // Group tasks by milestoneId.
    final byMilestone = <int?, List<Task>>{};
    for (final t in tasks) {
      (byMilestone[t.milestoneId] ??= []).add(t);
    }

    final unassigned = byMilestone[null] ?? [];

    if (tasks.isEmpty) {
      return Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Icon(LucideIcons.checkSquare,
                size: 48,
                color: Theme.of(context).colorScheme.onSurfaceVariant),
            const SizedBox(height: 12),
            Text(
              'No tasks in this project yet.',
              style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                    color: Theme.of(context).colorScheme.onSurfaceVariant,
                  ),
            ),
          ],
        ),
      );
    }

    return RefreshIndicator(
      onRefresh: () async {
        setState(() => _pendingStatus.clear());
        await Future.wait([
          ref.refresh(projectTasksProvider(widget.projectId).future),
          ref.refresh(projectMilestonesProvider(widget.projectId).future),
        ]);
      },
      child: CustomScrollView(
        slivers: [
          // Top colour strip.
          SliverToBoxAdapter(child: Container(height: 4, color: color)),

          // Milestone sections.
          for (final ms in milestones) ...[
            SliverToBoxAdapter(
              child: _MilestoneHeader(
                milestone: ms,
                tasks: byMilestone[ms.id] ?? [],
                color: color,
              ),
            ),
            if ((byMilestone[ms.id] ?? []).isNotEmpty)
              SliverList.builder(
                itemCount: byMilestone[ms.id]!.length,
                itemBuilder: (_, i) {
                  final task = byMilestone[ms.id]![i];
                  return _TaskRow(
                    task: task,
                    effectiveStatus: _effectiveStatus(task),
                    onStatusTap: () => _cycleStatus(task),
                    onTap: () => _openTask(task.id),
                  );
                },
              ),
          ],

          // Unassigned tasks.
          if (unassigned.isNotEmpty) ...[
            SliverToBoxAdapter(
              child: Padding(
                padding: const EdgeInsets.fromLTRB(16, 20, 16, 6),
                child: Text(
                  'No milestone',
                  style: Theme.of(context).textTheme.labelMedium?.copyWith(
                        color: Theme.of(context).colorScheme.onSurfaceVariant,
                        letterSpacing: 0.5,
                      ),
                ),
              ),
            ),
            SliverList.builder(
              itemCount: unassigned.length,
              itemBuilder: (_, i) {
                final task = unassigned[i];
                return _TaskRow(
                  task: task,
                  effectiveStatus: _effectiveStatus(task),
                  onStatusTap: () => _cycleStatus(task),
                  onTap: () => _openTask(task.id),
                );
              },
            ),
          ],

          const SliverToBoxAdapter(child: SizedBox(height: 16)),
        ],
      ),
    );
  }
}

// ── Milestone section header ──────────────────────────────────────────────────

class _MilestoneHeader extends StatelessWidget {
  final Milestone milestone;
  final List<Task> tasks;
  final Color color;

  const _MilestoneHeader({
    required this.milestone,
    required this.tasks,
    required this.color,
  });

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final done = tasks.where((t) => t.status == TaskStatus.done).length;
    final total = tasks.length;
    final pct = total > 0 ? done / total : 0.0;

    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 20, 16, 6),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Row(
            children: [
              Container(
                width: 10,
                height: 10,
                decoration: BoxDecoration(color: color, shape: BoxShape.circle),
              ),
              const SizedBox(width: 8),
              Expanded(
                child: Text(
                  milestone.title,
                  style: theme.textTheme.titleSmall,
                  maxLines: 1,
                  overflow: TextOverflow.ellipsis,
                ),
              ),
              const SizedBox(width: 8),
              Text(
                '$done / $total',
                style: theme.textTheme.labelSmall?.copyWith(
                  color: theme.colorScheme.onSurfaceVariant,
                ),
              ),
            ],
          ),
          if (total > 0) ...[
            const SizedBox(height: 4),
            LinearProgressIndicator(
              value: pct,
              minHeight: 2,
              color: color,
              backgroundColor: color.withValues(alpha: 0.15),
              borderRadius: BorderRadius.circular(1),
            ),
          ],
        ],
      ),
    );
  }
}

// ── Task row ──────────────────────────────────────────────────────────────────

class _TaskRow extends StatelessWidget {
  final Task task;
  final TaskStatus effectiveStatus;
  final VoidCallback onStatusTap;
  final VoidCallback onTap;

  const _TaskRow({
    required this.task,
    required this.effectiveStatus,
    required this.onStatusTap,
    required this.onTap,
  });

  IconData get _statusIcon => switch (effectiveStatus) {
        TaskStatus.done => LucideIcons.checkCircle2,
        TaskStatus.inProgress => LucideIcons.loader,
        TaskStatus.todo => LucideIcons.circle,
      };

  Color _statusColor(BuildContext context) {
    final cs = Theme.of(context).colorScheme;
    return switch (effectiveStatus) {
      TaskStatus.done => const Color(0xFF22C55E),
      TaskStatus.inProgress => cs.primary,
      TaskStatus.todo => cs.onSurfaceVariant,
    };
  }

  Color _priorityColor(BuildContext context) => switch (task.priority) {
        TaskPriority.high => const Color(0xFFEF4444),
        TaskPriority.medium => const Color(0xFFF59E0B),
        _ => Colors.transparent,
      };

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);

    return Card(
      margin: const EdgeInsets.symmetric(horizontal: 12, vertical: 3),
      child: InkWell(
        onTap: onTap,
        borderRadius: BorderRadius.circular(14),
        child: Padding(
          padding: const EdgeInsets.fromLTRB(4, 6, 14, 6),
          child: Row(
            children: [
              IconButton(
                icon: Icon(_statusIcon, color: _statusColor(context)),
                onPressed: onStatusTap,
                tooltip: 'Cycle status',
                visualDensity: VisualDensity.compact,
              ),
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Row(
                      children: [
                        Flexible(
                          child: Text(
                            task.title.isNotEmpty ? task.title : 'Untitled',
                            style: theme.textTheme.titleSmall?.copyWith(
                              decoration: effectiveStatus == TaskStatus.done
                                  ? TextDecoration.lineThrough
                                  : null,
                              color: effectiveStatus == TaskStatus.done
                                  ? theme.colorScheme.onSurfaceVariant
                                  : null,
                            ),
                            maxLines: 2,
                            overflow: TextOverflow.ellipsis,
                          ),
                        ),
                        PendingSyncBadge(
                          domain: kSyncDomainTasks,
                          id: task.id,
                        ),
                      ],
                    ),
                    if (task.dueDate != null) ...[
                      const SizedBox(height: 2),
                      Text(
                        'Due ${_formatDate(task.dueDate!)}',
                        style: theme.textTheme.labelSmall?.copyWith(
                          color: task.dueDate!.isBefore(DateTime.now()) &&
                                  effectiveStatus != TaskStatus.done
                              ? const Color(0xFFEF4444)
                              : theme.colorScheme.onSurfaceVariant,
                        ),
                      ),
                    ],
                  ],
                ),
              ),
              if (task.priority == TaskPriority.high ||
                  task.priority == TaskPriority.medium)
                Container(
                  width: 8,
                  height: 8,
                  decoration: BoxDecoration(
                    color: _priorityColor(context),
                    shape: BoxShape.circle,
                  ),
                ),
            ],
          ),
        ),
      ),
    );
  }
}

String _formatDate(DateTime dt) {
  const months = [
    'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
    'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec',
  ];
  return '${months[dt.month - 1]} ${dt.day}';
}