import 'dart:convert';
import 'dart:io';

import 'package:flutter/foundation.dart';

import '../models/channel_details.dart';

/// Robust public channel metadata fallback for Windows.
///
/// youtube_explode_dart currently returns enough metadata for some channels,
/// but on current YouTube layouts subscriber/about fields may be null. The
/// project already ships a current yt-dlp nightly for HD playback, so Windows
/// can reuse it without adding another dependency or a Google login.
class WindowsChannelMetadataService {
  WindowsChannelMetadataService._();

  static final WindowsChannelMetadataService instance =
      WindowsChannelMetadataService._();

  final Map<String, Future<ChannelDetails?>> _cache =
      <String, Future<ChannelDetails?>>{};

  Future<ChannelDetails?> getDetails(
    String channelId,
  ) {
    if (!Platform.isWindows || channelId.trim().isEmpty) {
      return Future<ChannelDetails?>.value(null);
    }

    return _cache.putIfAbsent(
      channelId,
      () => _load(channelId),
    );
  }

  void invalidate(String channelId) {
    _cache.remove(channelId);
  }

  Future<ChannelDetails?> _load(
    String channelId,
  ) async {
    final ytDlp = _resolveYtDlp();

    if (!await ytDlp.exists()) {
      debugPrint(
        '[CHANNEL-YTDLP][18.5.2] yt-dlp introuvable: ${ytDlp.path}',
      );
      return null;
    }

    Map<String, dynamic>? videosData;
    Map<String, dynamic>? aboutData;

    try {
      videosData = await _extract(
        ytDlp,
        'https://www.youtube.com/channel/$channelId/videos',
      );
    } catch (error) {
      debugPrint(
        '[CHANNEL-YTDLP][18.5.2] /videos échoué: $error',
      );
    }

    // Current yt-dlp channel extraction normally provides followers on the
    // channel URL. The About route can additionally expose channel views and
    // description on layouts where /videos omits them. It is intentionally
    // best-effort because YouTube has changed the About page several times.
    if (_intValue(videosData?['view_count']) == null ||
        _stringValue(videosData?['description']) == null) {
      try {
        aboutData = await _extract(
          ytDlp,
          'https://www.youtube.com/channel/$channelId/about',
        );
      } catch (error) {
        debugPrint(
          '[CHANNEL-YTDLP][18.5.2] /about ignoré: $error',
        );
      }
    }

    final data = _mergeMaps(
      primary: videosData,
      secondary: aboutData,
    );

    if (data == null) {
      return null;
    }

    final subscribers =
        _intValue(data['channel_follower_count']);
    final views = _intValue(data['view_count']);
    final rawVideoCount =
        _intValue(data['playlist_count']);
    final videoCount =
        rawVideoCount != null && rawVideoCount > 0
            ? rawVideoCount
            : null;

    final title =
        _stringValue(data['channel']) ??
        _stringValue(data['uploader']) ??
        _stringValue(data['title']) ??
        '';

    final description =
        _stringValue(data['description']) ?? '';

    final thumbnail = _bestThumbnail(
      data['thumbnails'],
    );

    debugPrint(
      '[CHANNEL-YTDLP][18.5.2] channel=$channelId '
      'subs=${subscribers ?? 'NA'} '
      'views=${views ?? 'NA'} '
      'videos=${videoCount ?? 'NA'} '
      'title=${title.isEmpty ? 'NA' : title}',
    );

    if (subscribers == null &&
        views == null &&
        videoCount == null &&
        title.isEmpty &&
        description.isEmpty) {
      return null;
    }

    return ChannelDetails(
      channelId: channelId,
      title: title,
      description: description,
      thumbnailUrl: thumbnail ?? '',
      viewCount: views,
      subscriberCount: subscribers,
      hiddenSubscriberCount: subscribers == null,
      videoCount: videoCount,
    );
  }

  Future<Map<String, dynamic>?> _extract(
    File ytDlp,
    String url,
  ) async {
    final args = <String>[
      '--ignore-config',
      '--quiet',
      '--no-warnings',
      '--encoding',
      'utf-8',
      '--socket-timeout',
      '15',
      '--retries',
      '2',
      '--flat-playlist',
      '--playlist-items',
      '0',
      '--skip-download',
      '--dump-single-json',
      url,
    ];

    final result = await Process.run(
      ytDlp.path,
      args,
      workingDirectory: ytDlp.parent.path,
      runInShell: false,
      stdoutEncoding: utf8,
      stderrEncoding: utf8,
    ).timeout(
      const Duration(seconds: 25),
    );

    if (result.exitCode != 0) {
      throw StateError(
        _compactError(result.stderr?.toString() ?? ''),
      );
    }

    final stdout = result.stdout?.toString().trim() ?? '';

    if (stdout.isEmpty) {
      return null;
    }

    // Normally --dump-single-json produces one JSON document. If yt-dlp ever
    // prints a harmless prefix, recover from the first opening brace.
    final jsonStart = stdout.indexOf('{');
    final jsonText = jsonStart >= 0
        ? stdout.substring(jsonStart)
        : stdout;

    final decoded = jsonDecode(jsonText);

    if (decoded is Map) {
      return Map<String, dynamic>.from(decoded);
    }

    return null;
  }

  Map<String, dynamic>? _mergeMaps({
    required Map<String, dynamic>? primary,
    required Map<String, dynamic>? secondary,
  }) {
    if (primary == null && secondary == null) {
      return null;
    }

    final merged = <String, dynamic>{};

    if (secondary != null) {
      merged.addAll(secondary);
    }

    if (primary != null) {
      // Prefer non-null values from /videos, but don't overwrite useful
      // About metadata with nulls.
      for (final entry in primary.entries) {
        if (entry.value != null) {
          merged[entry.key] = entry.value;
        }
      }
    }

    return merged;
  }

  File _resolveYtDlp() {
    final executableDirectory =
        File(Platform.resolvedExecutable).parent;

    final bundled = File(
      '${executableDirectory.path}'
      '${Platform.pathSeparator}data'
      '${Platform.pathSeparator}flutter_assets'
      '${Platform.pathSeparator}assets'
      '${Platform.pathSeparator}windows_hd'
      '${Platform.pathSeparator}yt-dlp.exe',
    );

    if (bundled.existsSync()) {
      return bundled;
    }

    return File(
      '${Directory.current.path}'
      '${Platform.pathSeparator}assets'
      '${Platform.pathSeparator}windows_hd'
      '${Platform.pathSeparator}yt-dlp.exe',
    );
  }

  int? _intValue(dynamic value) {
    if (value is int) {
      return value;
    }

    if (value is num) {
      return value.toInt();
    }

    if (value is String) {
      return int.tryParse(value);
    }

    return null;
  }

  String? _stringValue(dynamic value) {
    if (value == null) {
      return null;
    }

    final text = value.toString().trim();
    return text.isEmpty ? null : text;
  }

  String? _bestThumbnail(dynamic raw) {
    if (raw is! List || raw.isEmpty) {
      return null;
    }

    String? bestUrl;
    int bestArea = -1;

    for (final item in raw) {
      if (item is! Map) {
        continue;
      }

      final url = _stringValue(item['url']);
      if (url == null) {
        continue;
      }

      final width = _intValue(item['width']) ?? 0;
      final height = _intValue(item['height']) ?? 0;
      final area = width * height;

      if (bestUrl == null || area > bestArea) {
        bestUrl = url;
        bestArea = area;
      }
    }

    return bestUrl;
  }

  String _compactError(String value) {
    final normalized = value
        .replaceAll(RegExp(r'\s+'), ' ')
        .trim();

    if (normalized.length <= 350) {
      return normalized;
    }

    return '${normalized.substring(0, 350)}…';
  }
}