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

import 'package:crypto/crypto.dart' show sha256;
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';

import '../config/app_config.dart';

/// 模型目录条目（GET /api/v1/app/update 响应 data.models[]）。
/// 服务器发布模型后随版本检查一同下发，App 按目录逐数据集下载/更新。
class ModelCatalogItem {
  final int datasetId;
  final String datasetName;
  final String version;
  final List<String> labels;
  final int sizeBytes;
  final String sha256;
  final String downloadUrl;

  const ModelCatalogItem({
    required this.datasetId,
    required this.datasetName,
    required this.version,
    required this.labels,
    required this.sizeBytes,
    required this.sha256,
    required this.downloadUrl,
  });

  factory ModelCatalogItem.fromJson(Map<String, dynamic> j) =>
      ModelCatalogItem(
        datasetId: (j['datasetId'] as num?)?.toInt() ?? 0,
        datasetName: j['datasetName'] as String? ?? '',
        version: j['version'] as String? ?? '',
        labels: (j['labels'] as List? ?? const [])
            .map((e) => e.toString())
            .toList(),
        sizeBytes: (j['sizeBytes'] as num?)?.toInt() ?? 0,
        sha256: j['sha256'] as String? ?? '',
        downloadUrl: j['downloadUrl'] as String? ?? '',
      );
}

/// 已就绪模型（字节 + 标签，供推理 worker 加载；含内置资产回退模型）
class ModelBundle {
  final int datasetId;
  final String datasetName;
  final String version;
  final List<String> labels;
  final Uint8List bytes;

  const ModelBundle({
    required this.datasetId,
    required this.datasetName,
    required this.version,
    required this.labels,
    required this.bytes,
  });
}

/// 模型热更新管理：启动时拉取模型目录（随 /app/update 公开接口下发，无需登录态），
/// 按需下载/校验/持久化各数据集模型，供相机页多模型并行推理。
///
/// 存储：应用私有目录 `models/<datasetId>/`（model.tflite + labels.json + meta.json），
/// meta 记录 {version, sha256}，服务器发布新版本时按版本+摘要重下，不重复下载旧模型。
class ModelManager extends ChangeNotifier {
  static final ModelManager instance = ModelManager._();

  final String baseUrl;
  final http.Client _client;
  final Future<Directory> Function()? _rootDirOverride;

  List<ModelBundle> _models = const [];
  bool _ready = false;
  bool _refreshing = false;
  String? _error;
  Future<void>? _inFlight;

  ModelManager._({String? baseUrl, http.Client? client})
      : this(baseUrl: baseUrl, client: client);

  /// 可注入 baseUrl / client / 存储根目录（单测用）
  @visibleForTesting
  ModelManager({
    String? baseUrl,
    http.Client? client,
    Future<Directory> Function()? rootDir,
  })  : baseUrl = baseUrl ?? AppConfig.apiBaseUrl,
        _client = client ?? http.Client(),
        _rootDirOverride = rootDir;

  /// 已就绪模型列表（空 = 无服务器模型，回退内置资产）
  List<ModelBundle> get models => _models;

  /// 是否成功拉取过目录（即使下载失败也为 true，用于区分"从未联网"与"目录为空"）
  bool get ready => _ready;

  /// 最近一次同步的错误信息（下载失败/校验失败等；目录为空不算错误）
  String? get error => _error;

  bool get refreshing => _refreshing;

  /// 模型名摘要（诊断行展示）：内置 / 数据集名×n
  String get modelsLabel {
    if (_models.isEmpty) return '内置';
    return _models.map((m) => m.datasetName).join(',');
  }

  /// 拉取目录并同步本地模型；并发调用共享同一进行中的刷新。
  Future<void> refresh() {
    if (_refreshing) return _inFlight ?? Future.value();
    _refreshing = true;
    _inFlight = _doRefresh().whenComplete(() {
      _refreshing = false;
      _inFlight = null;
      notifyListeners();
    });
    return _inFlight!;
  }

  Future<void> _doRefresh() async {
    try {
      final res = await _client
          .get(Uri.parse('$baseUrl/api/v1/app/update'))
          .timeout(const Duration(seconds: 8));
      // 服务器 Content-Type 无 charset，http 包默认按 latin1 解码会乱码 → 显式 utf8
      final body =
          jsonDecode(utf8.decode(res.bodyBytes)) as Map<String, dynamic>;
      final data = body['data'] as Map<String, dynamic>? ?? const {};
      final list = data['models'] as List? ?? const [];
      final catalog = list
          .map((e) => ModelCatalogItem.fromJson(e as Map<String, dynamic>))
          .toList();

      final failed = <String>[];
      for (final item in catalog) {
        if (!await _ensureLocal(item)) failed.add(item.datasetName);
      }
      await _prune(catalog);
      _models = await _loadBundles(catalog);
      _ready = true;
      _error = failed.isEmpty
          ? null
          : '模型下载失败:${failed.join(',')}（重试旧模型或稍后再试）';
    } catch (e) {
      if (!_ready) _error = '模型目录拉取失败:$e';
      // 已就绪过则保留旧模型，不覆盖 error（下载级错误优先展示）
    }
  }

  /// 保证目录条目在本地可用：meta 匹配且文件在 → 跳过；否则下载并校验 sha256。
  Future<bool> _ensureLocal(ModelCatalogItem item) async {
    final dir = await _modelDir(item.datasetId);
    try {
      final meta = await _readMeta(dir);
      final file = File('${dir.path}/model.tflite');
      if (meta != null &&
          meta['version'] == item.version &&
          meta['sha256'] == item.sha256 &&
          await file.exists()) {
        return true;
      }
      // 版本更新或文件缺失：下载校验（失败重试一次）
      for (var attempt = 0; attempt < 2; attempt++) {
        final ok = await _downloadAndVerify(item, dir, file);
        if (ok) return true;
        await file.delete().catchError((_) => file);
        await File('${dir.path}/model.tflite.part')
            .delete()
            .catchError((_) => file);
      }
      debugPrint('[ModelManager] 下载失败: ${item.datasetName} ${item.version}');
      return false;
    } catch (e) {
      debugPrint('[ModelManager] _ensureLocal ${item.datasetName}: $e');
      return false;
    }
  }

  Future<bool> _downloadAndVerify(
      ModelCatalogItem item, Directory dir, File file) async {
    final part = File('${file.path}.part');
    final sink = part.openWrite();
    try {
      final res = await _client
          .send(http.Request('GET', Uri.parse('$baseUrl${item.downloadUrl}')))
          .timeout(const Duration(minutes: 3));
      if (res.statusCode != 200) return false;
      await res.stream.pipe(sink);
      await sink.close();
      final bytes = await part.readAsBytes();
      final hex = sha256.convert(bytes).toString();
      if (item.sha256.isNotEmpty && hex != item.sha256) {
        debugPrint('[ModelManager] sha256 不匹配: ${item.datasetName} '
            'want=${item.sha256} got=$hex');
        return false;
      }
      await part.rename(file.path);
      await dir.create(recursive: true);
      await File('${dir.path}/labels.json')
          .writeAsString(jsonEncode(item.labels));
      await File('${dir.path}/meta.json').writeAsString(jsonEncode({
        'version': item.version,
        'sha256': item.sha256,
      }));
      debugPrint('[ModelManager] 已下载 ${item.datasetName} '
          '${bytes.length}B -> ${file.path}');
      return true;
    } catch (e) {
      await sink.close().catchError((_) {});
      debugPrint('[ModelManager] 下载异常 ${item.datasetName}: $e');
      return false;
    }
  }

  /// 清理服务器目录中已下线的数据集模型（不再发布则删本地）
  Future<void> _prune(List<ModelCatalogItem> catalog) async {
    final root = await _rootDir();
    if (!await root.exists()) return;
    final keep = catalog.map((c) => '${c.datasetId}').toSet();
    await for (final e in root.list()) {
      if (e is Directory) {
        // 目录 URI 末尾带 '/'，pathSegments 末位为空串 → 过滤后取目录名
        final name = e.uri.pathSegments.where((s) => s.isNotEmpty).last;
        if (!keep.contains(name)) {
          await e.delete(recursive: true).catchError((_) => e);
        }
      }
    }
  }

  Future<List<ModelBundle>> _loadBundles(
      List<ModelCatalogItem> catalog) async {
    final bundles = <ModelBundle>[];
    for (final item in catalog) {
      try {
        final dir = await _modelDir(item.datasetId);
        final file = File('${dir.path}/model.tflite');
        if (!await file.exists()) continue;
        final labels = await File('${dir.path}/labels.json').exists()
            ? (jsonDecode(
                    await File('${dir.path}/labels.json').readAsString())
                as List)
                .map((e) => e.toString())
                .toList()
            : item.labels;
        bundles.add(ModelBundle(
          datasetId: item.datasetId,
          datasetName: item.datasetName,
          version: item.version,
          labels: labels,
          bytes: await file.readAsBytes(),
        ));
      } catch (e) {
        debugPrint('[ModelManager] 读取 ${item.datasetName} 失败: $e');
      }
    }
    return bundles;
  }

  Future<Map<String, dynamic>?> _readMeta(Directory dir) async {
    final f = File('${dir.path}/meta.json');
    if (!await f.exists()) return null;
    try {
      return jsonDecode(await f.readAsString()) as Map<String, dynamic>;
    } catch (_) {
      return null;
    }
  }

  Future<Directory> _rootDir() async {
    if (_rootDirOverride != null) return _rootDirOverride();
    final support = await getApplicationSupportDirectory();
    return Directory('${support.path}/models');
  }

  Future<Directory> _modelDir(int datasetId) async {
    final root = await _rootDir();
    final dir = Directory('${root.path}/$datasetId');
    await dir.create(recursive: true);
    return dir;
  }
}