import 'dart:async';
import 'dart:collection';
import 'dart:io';
import 'dart:typed_data';

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:just_audio/just_audio.dart';
import 'package:path_provider/path_provider.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:record/record.dart';

import 'api_client_provider.dart';

// ── Public helpers (also used by tests) ──────────────────────────────────────

class SentenceResult {
  final List<String> sentences;
  final String remainder;
  const SentenceResult({required this.sentences, required this.remainder});
}

/// Extract completed sentences from [text] at `.`, `!`, `?` boundaries.
/// Returns the completed sentences and the unconsumed remainder.
SentenceResult extractSentences(String text) {
  final boundary = RegExp(r'[.!?]+(?=\s|$)');
  final sentences = <String>[];
  var remaining = text;
  RegExpMatch? match;
  while ((match = boundary.firstMatch(remaining)) != null) {
    final end = match!.end;
    final sentence = remaining.substring(0, end).trim();
    if (sentence.isNotEmpty) sentences.add(sentence);
    remaining = remaining.substring(end).trimLeft();
  }
  return SentenceResult(sentences: sentences, remainder: remaining);
}

/// Strip markdown formatting before sending text to TTS.
String stripMarkdownForTts(String text) {
  return text
      .replaceAll(RegExp(r'```[\s\S]*?```'), '') // fenced code blocks
      .replaceAllMapped(RegExp(r'`([^`]+)`'), (m) => m[1]!) // inline code
      .replaceAll(RegExp(r'#{1,6}\s+'), '') // headings
      .replaceAllMapped(RegExp(r'\*\*([^*]+)\*\*'), (m) => m[1]!) // bold
      .replaceAllMapped(RegExp(r'\*([^*]+)\*'), (m) => m[1]!) // italic
      .replaceAllMapped(
          RegExp(r'\[([^\]]+)\]\([^)]+\)'), (m) => m[1]!) // links → text
      .replaceAll(RegExp(r'^\s*[-*+]\s+', multiLine: true), '') // list markers
      .replaceAll(RegExp(r'\n{2,}'), ' ') // multiple newlines → space
      .replaceAll('\n', ' ')
      .trim();
}

// ── State ─────────────────────────────────────────────────────────────────────

enum VoiceMode { idle, recording, transcribing, playing }

class VoiceState {
  final VoiceMode mode;
  final bool voiceModeActive;
  final bool available;

  const VoiceState({
    this.mode = VoiceMode.idle,
    this.voiceModeActive = false,
    this.available = true,
  });

  VoiceState copyWith({
    VoiceMode? mode,
    bool? voiceModeActive,
    bool? available,
  }) =>
      VoiceState(
        mode: mode ?? this.mode,
        voiceModeActive: voiceModeActive ?? this.voiceModeActive,
        available: available ?? this.available,
      );
}

// ── Provider ──────────────────────────────────────────────────────────────────

final voiceProvider =
    NotifierProvider<VoiceNotifier, VoiceState>(VoiceNotifier.new);

// ── Notifier ──────────────────────────────────────────────────────────────────

class VoiceNotifier extends Notifier<VoiceState> {
  // Audio I/O
  AudioRecorder? _recorder;
  AudioPlayer? _player;
  StreamSubscription<Amplitude>? _amplitudeSubscription;

  // Recording / silence detection
  int _recordingStartMs = 0;
  int _silenceMs = 0;
  static const _silenceThresholdDb = -40.0;
  static const _silenceDurationMs = 1500;
  static const _minRecordingMs = 300;

  // Voice mode callbacks
  Future<void> Function(String transcript)? _onTranscript;
  void Function(String message)? _onError;
  bool _enableTts = false;

  // Streaming TTS state
  String _sentenceBuffer = '';
  int _lastSeenLength = 0;
  bool _streamComplete = false;

  // Last complete assistant response — passed to Whisper as initial_prompt
  // to reduce STT mishearings of domain-specific words.
  String _lastAssistantContent = '';

  // TTS playback queue
  final _ttsQueue = Queue<Uint8List>();
  bool _ttsPlaying = false;
  int _ttsCounter = 0;
  Directory? _tempDir;

  @override
  VoiceState build() {
    _recorder = AudioRecorder();
    _player = AudioPlayer();
    ref.onDispose(() {
      _amplitudeSubscription?.cancel();
      _recorder?.dispose();
      _player?.dispose();
    });
    return const VoiceState();
  }

  // ── Public API ──────────────────────────────────────────────────────────────

  /// Enter voice mode. Checks server availability and mic permission first.
  /// [onTranscript] is called with the transcript when a recording completes.
  /// [enableTts] — if true, TTS plays when [feedContent] is called.
  /// [onError] — called with a human-readable message on failure.
  Future<void> enterVoiceMode({
    required Future<void> Function(String transcript) onTranscript,
    bool enableTts = false,
    required void Function(String message) onError,
  }) async {
    if (state.voiceModeActive) {
      exitVoiceMode();
      return;
    }

    // Check server availability
    try {
      final status = await ref.read(voiceRepositoryProvider).checkStatus();
      if (!status.fullyAvailable) {
        onError('Voice not available on this server');
        return;
      }
    } catch (_) {
      onError('Voice not available on this server');
      return;
    }

    // Check microphone permission
    final permStatus = await Permission.microphone.request();
    if (permStatus == PermissionStatus.denied ||
        permStatus == PermissionStatus.permanentlyDenied) {
      onError('Microphone permission required');
      if (permStatus == PermissionStatus.permanentlyDenied) {
        await openAppSettings();
      }
      return;
    }

    _onTranscript = onTranscript;
    _onError = onError;
    _enableTts = enableTts;
    _tempDir = await getTemporaryDirectory();

    state = state.copyWith(voiceModeActive: true, available: true);
    await _startListening();
  }

  /// Exit voice mode, stop all recording and TTS.
  void exitVoiceMode() {
    _amplitudeSubscription?.cancel();
    _amplitudeSubscription = null;
    _recorder?.stop();
    _player?.stop();
    _ttsQueue.clear();
    _ttsPlaying = false;
    _sentenceBuffer = '';
    _lastSeenLength = 0;
    _streamComplete = false;
    _onTranscript = null;
    _onError = null;
    state = const VoiceState();
  }

  /// Feed streaming assistant content for TTS synthesis.
  /// Call from screens with the full [fullContent] string on each update.
  /// Set [isComplete] to true when the stream has finished.
  void feedContent(String fullContent, {required bool isComplete}) {
    if (!state.voiceModeActive || !_enableTts) return;

    final delta = fullContent.length > _lastSeenLength
        ? fullContent.substring(_lastSeenLength)
        : '';
    _lastSeenLength = fullContent.length;
    _sentenceBuffer += delta;

    _dispatchSentences(flush: isComplete);

    if (isComplete) {
      _lastAssistantContent = fullContent;
      _streamComplete = true;
      _checkRestartListening();
    }
  }

  // ── Internal recording ──────────────────────────────────────────────────────

  Future<void> _startListening() async {
    if (!state.voiceModeActive) return;

    _silenceMs = 0;
    _recordingStartMs = DateTime.now().millisecondsSinceEpoch;
    state = state.copyWith(mode: VoiceMode.recording);

    final dir = _tempDir ?? await getTemporaryDirectory();
    // AAC/M4A is reliably supported on Android (unlike WebM/Opus which can
    // produce OGG bytes in a .webm file, confusing server-side decoders).
    final path =
        '${dir.path}/voice_rec_${DateTime.now().millisecondsSinceEpoch}.m4a';

    try {
      await _recorder!.start(
        const RecordConfig(encoder: AudioEncoder.aacLc, sampleRate: 16000),
        path: path,
      );

      _amplitudeSubscription?.cancel();
      _amplitudeSubscription = _recorder!
          .onAmplitudeChanged(const Duration(milliseconds: 200))
          .listen(_onAmplitude);
    } catch (e) {
      _onError?.call('Microphone error: could not start recording');
      exitVoiceMode();
    }
  }

  void _onAmplitude(Amplitude event) {
    if (!state.voiceModeActive) return;

    final elapsed =
        DateTime.now().millisecondsSinceEpoch - _recordingStartMs;
    if (elapsed < _minRecordingMs) return;

    final db = event.current;
    // Guard against NaN / ±Infinity which can arrive on some Android devices
    // when the recorder is initialising. Treat invalid readings as silence.
    final isSilent = db.isNaN || db.isInfinite || db < _silenceThresholdDb;

    if (isSilent) {
      _silenceMs += 200;
      if (_silenceMs >= _silenceDurationMs) {
        _amplitudeSubscription?.cancel();
        _amplitudeSubscription = null;
        _handleSilence();
      }
    } else {
      _silenceMs = 0;
    }
  }

  Future<void> _handleSilence() async {
    if (!state.voiceModeActive) return;
    state = state.copyWith(mode: VoiceMode.transcribing);

    final path = await _recorder!.stop();
    if (path == null || !state.voiceModeActive) return;

    try {
      final bytes = await File(path).readAsBytes();
      await File(path).delete().catchError((_) => File(path));

      if (!state.voiceModeActive) return;

      final transcript = await ref.read(voiceRepositoryProvider).transcribe(
            bytes,
            context: _lastAssistantContent.isNotEmpty ? _lastAssistantContent : null,
          );

      if (!state.voiceModeActive) return;

      if (transcript.isEmpty) {
        // Empty transcript — restart silently
        await _startListening();
        return;
      }

      // Reset TTS state for this new turn
      _sentenceBuffer = '';
      _lastSeenLength = 0;
      _streamComplete = false;

      if (_enableTts) {
        state = state.copyWith(mode: VoiceMode.playing);
      }

      await _onTranscript?.call(transcript);

      // If TTS is not enabled, loop immediately
      if (!_enableTts && state.voiceModeActive) {
        await _startListening();
      }
    } catch (e) {
      _onError?.call('Voice error: transcription failed');
      exitVoiceMode();
    }
  }

  // ── Internal TTS ────────────────────────────────────────────────────────────

  void _dispatchSentences({required bool flush}) {
    final result = extractSentences(_sentenceBuffer);
    _sentenceBuffer = flush ? '' : result.remainder;

    for (final sentence in result.sentences) {
      _enqueueSentence(sentence);
    }
    if (flush && result.remainder.trim().length >= 3) {
      _enqueueSentence(result.remainder.trim());
    }
  }

  void _enqueueSentence(String sentence) {
    final stripped = stripMarkdownForTts(sentence);
    if (stripped.length < 3) return;
    _synthesiseSentence(stripped);
  }

  Future<void> _synthesiseSentence(String text) async {
    try {
      final wavBytes =
          await ref.read(voiceRepositoryProvider).synthesise(text);
      if (!state.voiceModeActive) return;
      _ttsQueue.add(wavBytes);
      if (!_ttsPlaying) _drainTtsQueue();
    } catch (_) {
      // Skip failed sentence — TTS errors are non-fatal
    }
  }

  Future<void> _drainTtsQueue() async {
    if (_ttsPlaying) return;
    _ttsPlaying = true;
    final dir = _tempDir ?? await getTemporaryDirectory();

    try {
      while (_ttsQueue.isNotEmpty && state.voiceModeActive) {
        final wavBytes = _ttsQueue.removeFirst();
        final path = '${dir.path}/tts_${_ttsCounter++}.wav';
        final file = File(path);
        await file.writeAsBytes(wavBytes);

        try {
          await _player!.setFilePath(path);
          await _player!.play();
          await _player!.processingStateStream.firstWhere(
            (s) =>
                s == ProcessingState.completed || s == ProcessingState.idle,
          );
        } finally {
          await file.delete().catchError((_) => file);
        }
      }
    } finally {
      _ttsPlaying = false;
    }

    _checkRestartListening();
  }

  void _checkRestartListening() {
    if (_streamComplete &&
        _ttsQueue.isEmpty &&
        !_ttsPlaying &&
        state.voiceModeActive) {
      _streamComplete = false;
      _lastSeenLength = 0;
      _sentenceBuffer = '';
      _startListening();
    }
  }
}