import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:icalendar_parser/icalendar_parser.dart';
import 'package:path_provider/path_provider.dart';
import 'package:open_filex/open_filex.dart';
import 'package:universal_html/html.dart' as html;
import 'package:intl/intl.dart';

import '../models/cycle_entry.dart';

class IcsService {
  static Future<void> generateCycleCalendar(List<CycleEntry> entries) async {
    final iCalendar = ICalendar(
      properties: {
        'prodid': '-//Christian Period Tracker//NONSGML v1.0//EN',
        'version': '2.0',
        'calscale': 'GREGORIAN',
        'x-wr-calname': 'Cycle Tracking',
        'x-wr-timezone': DateTime.now().timeZoneName,
      },
      components: [],
    );

    // Sort entries by date to ensure proper calendar order
    entries.sort((a, b) => a.date.compareTo(b.date));

    for (var entry in entries) {
      if (entry.isPeriodDay) {
        final date = entry.date;
        final formattedDate = DateFormat('yyyyMMdd').format(date);
        final uid = '${date.year}${date.month}${date.day}-${entry.id}@christianperiodtracker.app';

        iCalendar.components.add(
          CalendarEvent(
            properties: {
              'uid': uid,
              'dtstamp': IcsDateTime(dt: DateTime.now()),
              'dtstart': IcsDateTime(dt: date, isUtc: false, date: true), // All-day event
              'dtend': IcsDateTime(dt: date.add(const Duration(days: 1)), isUtc: false, date: true), // End on next day for all-day
              'summary': 'Period Day',
              'description': 'Period tracking for ${DateFormat.yMMMd().format(date)}',
            },
          ),
        );
      }
    }

    final String icsContent = iCalendar.serialize();
    final String fileName = 'cycle_calendar_${DateFormat('yyyyMMdd').format(DateTime.now())}.ics';

    if (kIsWeb) {
      // Web platform
      final bytes = icsContent.codeUnits;
      final blob = html.Blob([bytes], 'text/calendar');
      final url = html.Url.createObjectUrlFromBlob(blob);
      html.AnchorElement(href: url)
        ..setAttribute('download', fileName)
        ..click();
      html.Url.revokeObjectUrl(url);
    } else {
      // Mobile platform
      final directory = await getApplicationDocumentsDirectory();
      final filePath = '${directory.path}/$fileName';
      final file = File(filePath);
      await file.writeAsString(icsContent);
      await OpenFilex.open(filePath);
    }
  }
}