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

import 'package:path_provider/path_provider.dart';

import '../models/message.dart';

/// Per-session JSON file persistence with debounced saves.
class MessageStore {
  MessageStore._();

  static Directory? _baseDir;
  static Timer? _debounceTimer;
  static final Map<String, List<Message>> _pendingSaves = {};

  /// Initialize the base directory for message storage.
  static Future<Directory> _getBaseDir() async {
    if (_baseDir != null) return _baseDir!;
    final appDir = await getApplicationDocumentsDirectory();
    _baseDir = Directory('${appDir.path}/messages');
    if (!await _baseDir!.exists()) {
      await _baseDir!.create(recursive: true);
    }
    return _baseDir!;
  }

  static String _fileForSession(String sessionId) {
    // Sanitize session ID for filename
    final safe = sessionId.replaceAll(RegExp(r'[^\w\-]'), '_');
    return 'session_$safe.json';
  }

  /// Save messages for a session with 1-second debounce.
  static void save(String sessionId, List<Message> messages) {
    _pendingSaves[sessionId] = messages;
    _debounceTimer?.cancel();
    _debounceTimer = Timer(const Duration(seconds: 1), _flushAll);
  }

  /// Immediately flush all pending saves.
  static Future<void> flush() async {
    _debounceTimer?.cancel();
    await _flushAll();
  }

  static Future<void> _flushAll() async {
    final entries = Map<String, List<Message>>.from(_pendingSaves);
    _pendingSaves.clear();

    for (final entry in entries.entries) {
      await _writeSession(entry.key, entry.value);
    }
  }

  static Future<void> _writeSession(
      String sessionId, List<Message> messages) async {
    try {
      final dir = await _getBaseDir();
      final file = File('${dir.path}/${_fileForSession(sessionId)}');
      // Strip heavy fields for persistence
      final lightMessages = messages.map((m) => m.toJsonLight()).toList();
      await file.writeAsString(jsonEncode(lightMessages));
    } catch (e) {
      // Silently fail - message persistence is best-effort
    }
  }

  /// Load messages for a session.
  /// [limit] controls how many recent messages to return (default: 50).
  /// [offset] is the number of messages to skip from the end (for pagination).
  static Future<List<Message>> load(
    String sessionId, {
    int limit = 50,
    int offset = 0,
  }) async {
    try {
      final dir = await _getBaseDir();
      final file = File('${dir.path}/${_fileForSession(sessionId)}');
      if (!await file.exists()) return [];

      final jsonStr = await file.readAsString();
      final List<dynamic> jsonList = jsonDecode(jsonStr) as List<dynamic>;
      final allMessages = jsonList
          .map((j) => _messageFromJson(j as Map<String, dynamic>))
          .where((m) => !m.isEmptyVoice && !m.isEmptyText)
          .toList();

      // Paginate from the end (newest messages first in storage)
      if (offset >= allMessages.length) return [];
      final end = allMessages.length - offset;
      final start = (end - limit).clamp(0, end);
      return allMessages.sublist(start, end);
    } catch (e) {
      return [];
    }
  }

  /// Load all messages for a session (no pagination).
  static Future<List<Message>> loadAll(String sessionId) async {
    try {
      final dir = await _getBaseDir();
      final file = File('${dir.path}/${_fileForSession(sessionId)}');
      if (!await file.exists()) return [];

      final jsonStr = await file.readAsString();
      final List<dynamic> jsonList = jsonDecode(jsonStr) as List<dynamic>;
      return jsonList
          .map((j) => _messageFromJson(j as Map<String, dynamic>))
          .where((m) => !m.isEmptyVoice && !m.isEmptyText)
          .toList();
    } catch (e) {
      return [];
    }
  }

  /// Deserialize a message from JSON, applying migration rules:
  /// - Voice messages without audioUri are downgraded to text (transcript only).
  ///   This handles messages saved before a restart, where the temp audio file
  ///   is no longer available. The transcript (content) is preserved.
  static Message _messageFromJson(Map<String, dynamic> json) {
    final raw = Message.fromJson(json);
    if (raw.type == MessageType.voice &&
        (raw.audioUri == null || raw.audioUri!.isEmpty)) {
      // Downgrade to text so the bubble shows the transcript instead of a
      // broken play button.
      return Message(
        id: raw.id,
        role: raw.role,
        type: MessageType.text,
        content: raw.content,
        timestamp: raw.timestamp,
        status: raw.status,
        duration: raw.duration,
      );
    }
    return raw;
  }

  /// Delete stored messages for a session.
  static Future<void> delete(String sessionId) async {
    try {
      final dir = await _getBaseDir();
      final file = File('${dir.path}/${_fileForSession(sessionId)}');
      if (await file.exists()) {
        await file.delete();
      }
    } catch (_) {}
  }

  /// Clear all stored messages.
  static Future<void> clearAll() async {
    try {
      final dir = await _getBaseDir();
      if (await dir.exists()) {
        await dir.delete(recursive: true);
        await dir.create(recursive: true);
      }
    } catch (_) {}
  }
}