import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';
import 'package:intl/intl.dart';
import 'package:mileograph_flutter/objects/objects.dart';
import 'package:mileograph_flutter/services/data_service.dart';
import 'package:provider/provider.dart';

part 'loco_timeline/timeline_grid.dart';
part 'loco_timeline/event_editor.dart';

class LocoTimelinePage extends StatefulWidget {
  const LocoTimelinePage({
    super.key,
    required this.locoId,
    required this.locoLabel,
  });

  final int locoId;
  final String locoLabel;

  @override
  State<LocoTimelinePage> createState() => _LocoTimelinePageState();
}

class _LocoTimelinePageState extends State<LocoTimelinePage> {
  final List<_EventDraft> _draftEvents = [];
  bool _isSaving = false;
  bool _isDeleting = false;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) => _load());
  }

  @override
  void dispose() {
    _disposeDrafts(_draftEvents);
    super.dispose();
  }

  Future<void> _load() {
    final data = context.read<DataService>();
    data.fetchEventFields();
    return data.fetchLocoTimeline(widget.locoId);
  }

  void _addDraftEvent() {
    setState(() {
      _draftEvents.add(_EventDraft());
    });
  }

  String? _eventDateForEntry(LocoAttrVersion entry) {
    final masked = entry.maskedValidFrom?.trim();
    if (masked != null && masked.isNotEmpty) return masked;
    final from = entry.validFrom ?? entry.txnFrom;
    if (from == null) return null;
    return DateFormat('yyyy-MM-dd').format(from);
  }

  EventField? _fieldForAttr(String attrCode, List<EventField> fields) {
    final normalized = attrCode.trim().toLowerCase();
    for (final field in fields) {
      if (field.name.trim().toLowerCase() == normalized) return field;
    }
    return null;
  }

  dynamic _valueForEntry(LocoAttrVersion entry) {
    if (entry.valueInt != null) return entry.valueInt;
    if (entry.valueBool != null) return entry.valueBool;
    if (entry.valueEnum != null && entry.valueEnum!.isNotEmpty) {
      return entry.valueEnum;
    }
    if (entry.valueStr != null && entry.valueStr!.isNotEmpty) {
      return entry.valueStr;
    }
    if (entry.valueDate != null) {
      return DateFormat('yyyy-MM-dd').format(entry.valueDate!);
    }
    if (entry.valueNorm != null && entry.valueNorm.toString().isNotEmpty) {
      return entry.valueNorm;
    }
    final label = entry.valueLabel;
    return label == '—' ? '' : label;
  }

  void _prefillDraftFromEntry(LocoAttrVersion entry, List<EventField> fields) {
    final dateStr = _eventDateForEntry(entry);
    if (dateStr == null || dateStr.isEmpty) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Cannot edit: timeline block date unknown.')),
      );
      return;
    }
    final field = _fieldForAttr(entry.attrCode, fields);
    if (field == null) {
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(
          content: Text(
            'Cannot edit: no event field found for ${_formatAttrLabel(entry.attrCode)}.',
          ),
        ),
      );
      return;
    }

    final draft = _EventDraft();
    draft.dateController.text = dateStr;
    draft.detailsController.text = '';
    draft.details = '';
    draft.fields.add(
      _FieldEntry(field: field)
        ..value = _valueForEntry(entry),
    );

    setState(() {
      _draftEvents.add(draft);
    });
  }

  Future<void> _deleteEntry(LocoAttrVersion entry) async {
    if (_isDeleting) return;
    final blockId = entry.versionId;
    if (blockId == null) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Cannot delete: timeline block has no ID.')),
      );
      return;
    }

    final data = context.read<DataService>();
    final messenger = ScaffoldMessenger.of(context);

    final dateStr = _eventDateForEntry(entry);
    final ok = await showDialog<bool>(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: const Text('Delete timeline block?'),
          content: Text(
            dateStr == null || dateStr.isEmpty
                ? 'This will delete the selected block for ${_formatAttrLabel(entry.attrCode)}.'
                : 'This will delete the block for ${_formatAttrLabel(entry.attrCode)} starting at $dateStr.',
          ),
          actions: [
            TextButton(
              onPressed: () => Navigator.of(context).pop(false),
              child: const Text('Cancel'),
            ),
            FilledButton(
              onPressed: () => Navigator.of(context).pop(true),
              child: const Text('Delete'),
            ),
          ],
        );
      },
    );
    if (ok != true) return;
    if (!mounted) return;

    setState(() {
      _isDeleting = true;
    });
    try {
      await data.deleteTimelineBlock(
        blockId: blockId,
      );
      await _load();
      if (mounted) {
        messenger.showSnackBar(
          const SnackBar(content: Text('Timeline block deleted')),
        );
      }
    } catch (e) {
      if (mounted) {
        messenger.showSnackBar(
          SnackBar(content: Text('Failed to delete timeline block: $e')),
        );
      }
    } finally {
      if (mounted) {
        setState(() {
          _isDeleting = false;
        });
      }
    }
  }

  void _removeDraftAt(int index) {
    if (index < 0 || index >= _draftEvents.length) return;
    final draft = _draftEvents.removeAt(index);
    _disposeDraft(draft);
    setState(() {});
  }

  void _disposeDraft(_EventDraft draft) {
    draft.dateController.dispose();
    draft.detailsController.dispose();
  }

  void _disposeDrafts(List<_EventDraft> drafts) {
    for (final draft in drafts) {
      _disposeDraft(draft);
    }
  }

  Future<void> _saveEvents() async {
    if (_isSaving) return;
    if (!_canSaveDrafts()) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Please fix validation issues before saving.')),
      );
      return;
    }
    final data = context.read<DataService>();
    setState(() {
      _isSaving = true;
    });
    try {
      final invalid = <String>[];
      for (final draft in _draftEvents) {
        final dateStr = draft.dateController.text.trim();
        if (!_isValidDateString(dateStr)) {
          invalid.add('Date is invalid (${dateStr.isEmpty ? 'empty' : dateStr})');
          continue;
        }
        if (draft.fields.isEmpty) {
          invalid.add('Add at least one field for each event');
          continue;
        }
        final values = <String, dynamic>{};
        for (final field in draft.fields) {
          final val = field.value;
          final isBlankString = val is String && val.trim().isEmpty;
          if (val == null || isBlankString) {
            invalid.add('Field ${field.field.display} is empty');
            break;
          }
          values[field.field.name] = val;
        }
        if (invalid.isNotEmpty) continue;
        if (values.isEmpty) {
          invalid.add('Add at least one value');
          continue;
        }
        await data.createLocoEvent(
          locoId: widget.locoId,
          eventDate: dateStr,
          values: values,
          details: draft.details,
        );
      }
      if (invalid.isNotEmpty) {
        if (mounted) {
          ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(content: Text(invalid.first)),
          );
        }
        return;
      }
      _disposeDrafts(_draftEvents);
      _draftEvents.clear();
      await _load();
      if (mounted) {
        ScaffoldMessenger.of(context).showSnackBar(
          const SnackBar(content: Text('Events saved')),
        );
      }
    } catch (e) {
      if (mounted) {
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: Text('Failed to save events: $e')),
        );
      }
    } finally {
      if (mounted) {
        setState(() {
          _isSaving = false;
        });
      }
    }
  }

  bool _isValidDateString(String input) {
    final trimmed = input.trim();
    final regex = RegExp(r'^\d{4}-(\d{2}|xx|XX)-(\d{2}|xx|XX)$');
    if (!regex.hasMatch(trimmed)) return false;
    final parts = trimmed.split('-');
    final monthPart = parts[1];
    final dayPart = parts[2];
    final monthUnknown = monthPart.toLowerCase() == 'xx';
    final dayUnknown = dayPart.toLowerCase() == 'xx';
    if (monthUnknown && !dayUnknown) return false;
    if (!monthUnknown) {
      final month = int.tryParse(monthPart);
      if (month == null || month < 1 || month > 12) return false;
    }
    if (!dayUnknown) {
      final day = int.tryParse(dayPart);
      if (day == null || day < 1 || day > 31) return false;
    }
    return true;
  }

  bool _draftIsValid(_EventDraft draft) {
    final dateStr = draft.dateController.text.trim();
    if (!_isValidDateString(dateStr)) return false;
    if (draft.fields.isEmpty) return false;
    for (final field in draft.fields) {
      final val = field.value;
      if (val == null) return false;
      if (val is String && val.trim().isEmpty) return false;
    }
    return true;
  }

  bool _canSaveDrafts() {
    if (_draftEvents.isEmpty) return false;
    return _draftEvents.every(_draftIsValid);
  }

  @override
  Widget build(BuildContext context) {
    final data = context.watch<DataService>();
    final timeline = data.timelineForLoco(widget.locoId);
    final isLoading = data.isLocoTimelineLoading(widget.locoId);

    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: const Icon(Icons.arrow_back),
          onPressed: () => Navigator.of(context).maybePop(),
        ),
        title: Text('Timeline · ${widget.locoLabel}'),
      ),
      body: RefreshIndicator(
        onRefresh: _load,
        child: LayoutBuilder(
          builder: (context, constraints) {
            if (isLoading && timeline.isEmpty) {
              return const Center(child: CircularProgressIndicator());
            }
            if (timeline.isEmpty) {
              return Padding(
                padding: const EdgeInsets.all(16.0),
                child: Card(
                  child: Padding(
                    padding: const EdgeInsets.all(16.0),
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: [
                        Text(
                          'No timeline data yet',
                          style: Theme.of(context).textTheme.titleMedium?.copyWith(
                                fontWeight: FontWeight.w700,
                              ),
                        ),
                        const SizedBox(height: 8),
                        const Text(
                          'This locomotive does not have any attribute history to show right now.',
                        ),
                        const SizedBox(height: 12),
                        OutlinedButton.icon(
                          onPressed: _load,
                          icon: const Icon(Icons.refresh),
                          label: const Text('Try again'),
                        ),
                      ],
                    ),
                  ),
                ),
              );
            }
            return ListView(
              padding: const EdgeInsets.all(16),
              children: [
                _TimelineGrid(
                  entries: timeline,
                  onEditEntry: (entry) => _prefillDraftFromEntry(
                    entry,
                    data.eventFields,
                  ),
                  onDeleteEntry: _deleteEntry,
                ),
                const SizedBox(height: 16),
                _EventEditor(
                  eventFields: data.eventFields,
                  drafts: _draftEvents,
                  onAddEvent: _addDraftEvent,
                  onChange: () => setState(() {}),
                  onSave: _saveEvents,
                  onRemoveDraft: _removeDraftAt,
                  isSaving: _isSaving,
                  canSave: _canSaveDrafts(),
                ),
              ],
            );
          },
        ),
      ),
    );
  }
}