import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';
import 'package:intl/intl.dart';

import '../../../../app/di/injection.dart';
import '../../../../features/calendar/data/repositories/calendar_repository.dart';
import '../../../../features/calendar/data/models/schedule_item_model.dart';
import '../../../../core/l10n/l10n.dart';
import '../../../../core/theme/design_tokens.dart';
import '../../../../shared/widgets/app_button.dart';
import '../../../../shared/widgets/app_pressable.dart';
import '../../../../shared/widgets/app_sheet_input_field.dart';
import '../../../../shared/widgets/back_title_page_header.dart';
import '../../../../shared/widgets/error_retry_surface.dart';
import '../../../../shared/widgets/full_screen_loading.dart';
import '../../../../shared/widgets/toast/toast.dart';
import '../../../../shared/widgets/toast/toast_type.dart';
import '../../data/apis/todo_api.dart';

class TodoEditScreen extends StatefulWidget {
  final String? todoId;

  const TodoEditScreen({super.key, required this.todoId});

  const TodoEditScreen.create({super.key}) : todoId = null;

  bool get isCreateMode => todoId == null;

  @override
  State<TodoEditScreen> createState() => _TodoEditScreenState();
}

class _TodoEditScreenState extends State<TodoEditScreen> {
  final TodoApi _todoApi = sl<TodoApi>();
  final CalendarRepository _calendarRepository = sl<CalendarRepository>();

  final TextEditingController _titleController = TextEditingController();
  final TextEditingController _descriptionController = TextEditingController();

  TodoResponse? _todo;
  bool _loading = true;
  bool _saving = false;
  String? _error;

  int _priority = 1;
  final Set<String> _selectedScheduleItemIds = <String>{};
  List<_ScheduleItemSimple> _scheduleItems = const <_ScheduleItemSimple>[];

  ColorScheme get _colorScheme => Theme.of(context).colorScheme;

  @override
  void initState() {
    super.initState();
    _loadPage();
  }

  @override
  void dispose() {
    _titleController.dispose();
    _descriptionController.dispose();
    super.dispose();
  }

  Future<void> _loadPage() async {
    setState(() {
      _loading = true;
      _error = null;
    });

    try {
      final now = DateTime.now();
      final start = now.subtract(const Duration(days: 30));
      final end = now.add(const Duration(days: 90));
      final scheduleItems = await _calendarRepository.listByRange(
        startAt: start,
        endAt: end,
      );

      TodoResponse? todo;
      if (!widget.isCreateMode) {
        todo = await _todoApi.getTodo(widget.todoId!);
      }

      if (!mounted) {
        return;
      }

      _todo = todo;
      _titleController.text = todo?.title ?? '';
      _descriptionController.text = todo?.description ?? '';
      _priority = todo?.priority ?? 1;
      _selectedScheduleItemIds
        ..clear()
        ..addAll(todo?.scheduleItems.map((item) => item.id) ?? const []);
      _scheduleItems = scheduleItems
          .where((item) => item.status == ScheduleStatus.active)
          .map(
            (item) => _ScheduleItemSimple(
              id: item.id,
              title: item.title,
              startAt: item.startAt,
            ),
          )
          .toList();

      setState(() {
        _loading = false;
      });
    } catch (error) {
      if (!mounted) {
        return;
      }
      setState(() {
        _loading = false;
        _error = error.toString();
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: _colorScheme.surface,
      resizeToAvoidBottomInset: false,
      body: SafeArea(
        child: GestureDetector(
          behavior: HitTestBehavior.translucent,
          onTap: () => FocusScope.of(context).unfocus(),
          child: Container(
            decoration: BoxDecoration(
              gradient: LinearGradient(
                begin: Alignment.topCenter,
                end: Alignment.bottomCenter,
                colors: [
                  _colorScheme.surfaceContainerLow,
                  _colorScheme.surface,
                ],
              ),
            ),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.stretch,
              children: [
                BackTitlePageHeader(
                  title: widget.isCreateMode
                      ? context.l10n.todoCreateTitle
                      : context.l10n.todoEditTitle,
                ),
                Expanded(child: _buildBody()),
                _buildBottomAction(),
              ],
            ),
          ),
        ),
      ),
    );
  }

  Widget _buildBody() {
    if (_loading) {
      return const FullScreenLoading();
    }

    if (_error != null) {
      return ErrorRetrySurface(
        message: context.l10n.commonLoadFailed(_error!),
        onRetry: _loadPage,
      );
    }

    if (!widget.isCreateMode && _todo == null) {
      return Center(child: Text(context.l10n.todoNotFound));
    }

    return ListView(
      padding: const EdgeInsets.fromLTRB(
        AppSpacing.lg,
        AppSpacing.sm,
        AppSpacing.lg,
        AppSpacing.lg,
      ),
      children: [
        _buildHeaderCard(),
        const SizedBox(height: AppSpacing.md),
        _buildFormCard(),
        const SizedBox(height: AppSpacing.md),
        _buildScheduleCard(),
      ],
    );
  }

  Widget _buildHeaderCard() {
    final headerDesc = widget.isCreateMode
        ? context.l10n.todoInfoDescCreate
        : _todo?.status == 'done'
        ? context.l10n.todoInfoDescDone
        : context.l10n.todoInfoDescDefault;

    return Container(
      padding: const EdgeInsets.all(AppSpacing.lg),
      decoration: BoxDecoration(
        color: _colorScheme.surface,
        borderRadius: BorderRadius.circular(AppRadius.xl),
        border: Border.all(color: _colorScheme.outlineVariant),
        boxShadow: [
          BoxShadow(
            color: _colorScheme.shadow.withValues(alpha: 0.18),
            blurRadius: AppRadius.lg,
            offset: const Offset(0, AppSpacing.xs),
          ),
        ],
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Text(
            context.l10n.todoInfoTitle,
            style: TextStyle(
              fontSize: 18,
              fontWeight: FontWeight.w700,
              color: _colorScheme.onSurface,
            ),
          ),
          const SizedBox(height: AppSpacing.xs),
          Text(
            headerDesc,
            style: TextStyle(
              fontSize: 13,
              color: _colorScheme.onSurfaceVariant,
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildFormCard() {
    return Container(
      padding: const EdgeInsets.all(AppSpacing.lg),
      decoration: BoxDecoration(
        color: _colorScheme.surface,
        borderRadius: BorderRadius.circular(AppRadius.xl),
        border: Border.all(color: _colorScheme.outlineVariant),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          AppSheetInputField(
            controller: _titleController,
            label: context.l10n.todoFieldTitle,
            hint: context.l10n.todoFieldTitleHint,
          ),
          const SizedBox(height: AppSpacing.lg),
          AppSheetInputField(
            controller: _descriptionController,
            label: context.l10n.todoFieldDescriptionOptional,
            hint: context.l10n.todoFieldDescriptionHint,
            maxLines: 2,
          ),
          const SizedBox(height: AppSpacing.lg),
          Text(
            context.l10n.todoPriority,
            style: TextStyle(
              fontSize: 14,
              fontWeight: FontWeight.w600,
              color: _colorScheme.onSurface,
            ),
          ),
          const SizedBox(height: AppSpacing.sm),
          Wrap(
            spacing: AppSpacing.sm,
            runSpacing: AppSpacing.sm,
            children: [
              _PriorityPill(
                label: context.l10n.todoQuadrantImportantUrgent,
                selected: _priority == 1,
                borderColor: _colorScheme.error,
                activeColor: _colorScheme.error,
                onTap: () => setState(() => _priority = 1),
              ),
              _PriorityPill(
                label: context.l10n.todoQuadrantUrgentNotImportant,
                selected: _priority == 3,
                borderColor: _colorScheme.primary,
                activeColor: _colorScheme.primary,
                onTap: () => setState(() => _priority = 3),
              ),
              _PriorityPill(
                label: context.l10n.todoQuadrantImportantNotUrgent,
                selected: _priority == 2,
                borderColor: _colorScheme.tertiary,
                activeColor: _colorScheme.tertiary,
                onTap: () => setState(() => _priority = 2),
              ),
            ],
          ),
        ],
      ),
    );
  }

  Widget _buildScheduleCard() {
    return Container(
      padding: const EdgeInsets.all(AppSpacing.lg),
      decoration: BoxDecoration(
        color: _colorScheme.surfaceContainerLow,
        borderRadius: BorderRadius.circular(AppRadius.xl),
        border: Border.all(color: _colorScheme.outlineVariant),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Row(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              Text(
                context.l10n.todoLinkedCalendarEvents,
                style: TextStyle(
                  fontSize: 14,
                  fontWeight: FontWeight.w600,
                  color: _colorScheme.onSurface,
                ),
              ),
              const Spacer(),
              Text(
                context.l10n.todoItemCount(_selectedScheduleItemIds.length),
                style: TextStyle(
                  fontSize: 12,
                  fontWeight: FontWeight.w600,
                  color: _colorScheme.onSurfaceVariant,
                ),
              ),
            ],
          ),
          const SizedBox(height: AppSpacing.sm),
          if (_scheduleItems.isEmpty)
            Padding(
              padding: EdgeInsets.symmetric(vertical: AppSpacing.xl),
              child: Center(
                child: Text(
                  context.l10n.todoNoSelectableCalendarEvents,
                  style: TextStyle(color: _colorScheme.onSurfaceVariant),
                ),
              ),
            )
          else
            ConstrainedBox(
              constraints: const BoxConstraints(maxHeight: 280),
              child: ListView.separated(
                shrinkWrap: true,
                itemCount: _scheduleItems.length,
                separatorBuilder: (context, index) =>
                    const SizedBox(height: AppSpacing.sm),
                itemBuilder: (context, index) {
                  final item = _scheduleItems[index];
                  final selected = _selectedScheduleItemIds.contains(item.id);
                  return _ScheduleSelectableTile(
                    title: item.title,
                    subtitle: _formatDate(item.startAt),
                    selected: selected,
                    onTap: () {
                      setState(() {
                        if (selected) {
                          _selectedScheduleItemIds.remove(item.id);
                        } else {
                          _selectedScheduleItemIds.add(item.id);
                        }
                      });
                    },
                  );
                },
              ),
            ),
        ],
      ),
    );
  }

  Widget _buildBottomAction() {
    final canSave = !_loading && !_saving;
    return Container(
      padding: const EdgeInsets.fromLTRB(
        AppSpacing.lg,
        AppSpacing.sm,
        AppSpacing.lg,
        AppSpacing.lg,
      ),
      decoration: BoxDecoration(
        color: _colorScheme.surface.withValues(alpha: 0.9),
        border: Border(top: BorderSide(color: _colorScheme.outlineVariant)),
      ),
      child: AppButton(
        text: _saving
            ? context.l10n.todoSaveInProgress
            : (widget.isCreateMode
                  ? context.l10n.todoCreateButton
                  : context.l10n.todoSaveChanges),
        onPressed: canSave ? _save : null,
      ),
    );
  }

  Future<void> _save() async {
    if (_saving) {
      return;
    }
    final title = _titleController.text.trim();
    if (title.isEmpty) {
      Toast.show(context, context.l10n.todoEnterTitle, type: ToastType.warning);
      return;
    }

    setState(() {
      _saving = true;
    });

    try {
      final description = _descriptionController.text.trim().isEmpty
          ? null
          : _descriptionController.text.trim();
      if (widget.isCreateMode) {
        await _todoApi.createTodo(
          title: title,
          description: description,
          priority: _priority,
          scheduleItemIds: _selectedScheduleItemIds.toList(),
        );
      } else {
        await _todoApi.updateTodo(
          widget.todoId!,
          title: title,
          description: description,
          priority: _priority,
          scheduleItemIds: _selectedScheduleItemIds.toList(),
        );
      }
      if (!mounted) {
        return;
      }
      context.pop(true);
    } catch (error) {
      if (!mounted) {
        return;
      }
      Toast.show(
        context,
        context.l10n.todoSaveFailed(error.toString()),
        type: ToastType.error,
      );
    } finally {
      if (mounted) {
        setState(() {
          _saving = false;
        });
      }
    }
  }

  String _formatDate(DateTime dt) {
    return DateFormat.yMd(context.l10n.localeName).add_Hm().format(dt);
  }
}

class _ScheduleItemSimple {
  final String id;
  final String title;
  final DateTime startAt;

  const _ScheduleItemSimple({
    required this.id,
    required this.title,
    required this.startAt,
  });
}

class _PriorityPill extends StatelessWidget {
  final String label;
  final bool selected;
  final Color borderColor;
  final Color activeColor;
  final VoidCallback onTap;

  const _PriorityPill({
    required this.label,
    required this.selected,
    required this.borderColor,
    required this.activeColor,
    required this.onTap,
  });

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

    return AppPressable(
      onTap: onTap,
      borderRadius: BorderRadius.circular(AppRadius.full),
      child: AnimatedContainer(
        duration: const Duration(milliseconds: 140),
        curve: Curves.easeOut,
        padding: const EdgeInsets.symmetric(
          horizontal: AppSpacing.md,
          vertical: AppSpacing.sm,
        ),
        decoration: BoxDecoration(
          color: selected
              ? borderColor.withValues(alpha: 0.28)
              : colorScheme.surface,
          borderRadius: BorderRadius.circular(AppRadius.full),
          border: Border.all(
            color: selected ? borderColor : colorScheme.outlineVariant,
            width: selected ? 1.5 : 1,
          ),
        ),
        child: Text(
          label,
          style: TextStyle(
            fontSize: 12,
            fontWeight: selected ? FontWeight.w600 : FontWeight.w500,
            color: selected ? activeColor : colorScheme.onSurfaceVariant,
          ),
        ),
      ),
    );
  }
}

class _ScheduleSelectableTile extends StatelessWidget {
  final String title;
  final String subtitle;
  final bool selected;
  final VoidCallback onTap;

  const _ScheduleSelectableTile({
    required this.title,
    required this.subtitle,
    required this.selected,
    required this.onTap,
  });

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

    return AppPressable(
      onTap: onTap,
      borderRadius: BorderRadius.circular(AppRadius.lg),
      child: AnimatedContainer(
        duration: const Duration(milliseconds: 120),
        curve: Curves.easeOut,
        padding: const EdgeInsets.all(AppSpacing.md),
        decoration: BoxDecoration(
          color: selected ? colorScheme.primaryContainer : colorScheme.surface,
          borderRadius: BorderRadius.circular(AppRadius.lg),
          border: Border.all(
            color: selected ? colorScheme.primary : colorScheme.outlineVariant,
          ),
        ),
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            Expanded(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(
                    title,
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                    style: TextStyle(
                      fontSize: 13,
                      fontWeight: FontWeight.w600,
                      color: colorScheme.onSurface,
                    ),
                  ),
                  const SizedBox(height: AppSpacing.xs),
                  Text(
                    subtitle,
                    style: TextStyle(
                      fontSize: 12,
                      color: colorScheme.onSurfaceVariant,
                    ),
                  ),
                ],
              ),
            ),
            const SizedBox(width: AppSpacing.md),
            AnimatedContainer(
              duration: const Duration(milliseconds: 120),
              width: AppSpacing.lg,
              height: AppSpacing.lg,
              decoration: BoxDecoration(
                color: selected ? colorScheme.primary : colorScheme.surface,
                borderRadius: BorderRadius.circular(AppRadius.full),
                border: Border.all(
                  color: selected
                      ? colorScheme.primary
                      : colorScheme.outlineVariant,
                ),
              ),
              child: selected
                  ? Icon(Icons.check, size: 12, color: colorScheme.onPrimary)
                  : null,
            ),
          ],
        ),
      ),
    );
  }
}