mnemo_cards/mnemo_cards_backend/lib/packs/voice_storage.dart

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

import 'package:mnemo_cards_backend/packs/pack_manager.dart'
    show PackManagerUtils;

/// Utilities for storing and serving voice audio files.
///
/// **Invariant**: `voice_models.voice_url` should store a **path-like reference**
/// (usually a file name inside `data/voice/`) or a remote URL, never raw base64.
class VoiceStorage {
  const VoiceStorage();

  static final _base64Regex = RegExp(r'^[A-Za-z0-9+/]*={0,2}$');

  static bool isRemoteUrl(String value) {
    final v = value.trim();
    return v.startsWith('http://') || v.startsWith('https://');
  }

  /// Accepts:
  /// - `file.mp3`
  /// - `voice/file.mp3`
  /// - `/voice/file.mp3`
  ///
  /// Returns sanitized file name (without any directories) or `null`.
  static String? sanitizeVoiceFileName(String value) {
    final normalized = value
        .trim()
        .replaceAll('\\', '/')
        .replaceFirst(RegExp('^/'), '');
    if (normalized.isEmpty) return null;
    if (normalized.contains('..')) return null;

    final withoutPrefix = normalized.startsWith('voice/')
        ? normalized.substring('voice/'.length)
        : normalized;

    // We only allow a plain file name here.
    if (withoutPrefix.contains('/')) return null;

    return withoutPrefix.isEmpty ? null : withoutPrefix;
  }

  static ParsedVoiceAudio? tryParseBase64Audio(String value) {
    final v = value.trim();
    if (v.isEmpty) return null;

    if (v.startsWith('data:')) {
      final commaIndex = v.indexOf(',');
      if (commaIndex <= 0) return null;
      final header = v.substring(0, commaIndex);
      final payload = v.substring(commaIndex + 1);

      if (!header.contains(';base64')) return null;

      final bytes = _decodeBase64(payload);
      if (bytes == null) return null;

      final contentType =
          _contentTypeFromDataUrlHeader(header) ??
          _detectContentType(bytes) ??
          'audio/mpeg';
      final ext = _extensionFromContentType(contentType) ?? 'mp3';

      return ParsedVoiceAudio(bytes: bytes, contentType: contentType, ext: ext);
    }

    // Plain base64 (no data URL header)
    if (v.length < 50) return null;
    if (!_base64Regex.hasMatch(v)) return null;

    final bytes = _decodeBase64(v);
    if (bytes == null) return null;

    final contentType = _detectContentType(bytes) ?? 'audio/mpeg';
    final ext = _extensionFromContentType(contentType) ?? 'mp3';
    return ParsedVoiceAudio(bytes: bytes, contentType: contentType, ext: ext);
  }

  static Uint8List? _decodeBase64(String input) {
    try {
      // normalize() fixes missing padding (=) and whitespace issues.
      final normalized = base64.normalize(input.trim());
      return base64Decode(normalized);
    } catch (_) {
      return null;
    }
  }

  static String? _contentTypeFromDataUrlHeader(String header) {
    // Example: data:audio/mpeg;base64
    final match = RegExp(r'^data:([^;]+);base64$').firstMatch(header);
    return match?.group(1);
  }

  static String? _detectContentType(Uint8List bytes) {
    if (bytes.length >= 12) {
      // MP3: "ID3" tag or frame sync (0xFF 0xFB / 0xF3 / 0xF2)
      if (bytes[0] == 0x49 && bytes[1] == 0x44 && bytes[2] == 0x33) {
        return 'audio/mpeg';
      }
      if (bytes[0] == 0xFF &&
          (bytes[1] == 0xFB || bytes[1] == 0xF3 || bytes[1] == 0xF2)) {
        return 'audio/mpeg';
      }

      // WAV: "RIFF....WAVE"
      if (bytes[0] == 0x52 &&
          bytes[1] == 0x49 &&
          bytes[2] == 0x46 &&
          bytes[3] == 0x46 &&
          bytes[8] == 0x57 &&
          bytes[9] == 0x41 &&
          bytes[10] == 0x56 &&
          bytes[11] == 0x45) {
        return 'audio/wav';
      }

      // OGG: "OggS"
      if (bytes[0] == 0x4F &&
          bytes[1] == 0x67 &&
          bytes[2] == 0x67 &&
          bytes[3] == 0x53) {
        return 'audio/ogg';
      }

      // FLAC: "fLaC"
      if (bytes[0] == 0x66 &&
          bytes[1] == 0x4C &&
          bytes[2] == 0x61 &&
          bytes[3] == 0x43) {
        return 'audio/flac';
      }
    }

    return null;
  }

  static String? _extensionFromContentType(String contentType) {
    return switch (contentType) {
      'audio/mpeg' => 'mp3',
      'audio/mp3' => 'mp3',
      'audio/wav' => 'wav',
      'audio/x-wav' => 'wav',
      'audio/ogg' => 'ogg',
      'audio/flac' => 'flac',
      _ => null,
    };
  }

  static String _defaultFileName({
    required String voiceId,
    required String ext,
  }) {
    return '$voiceId.$ext';
  }

  static Directory _assetsDirectory(Directory? override) {
    return override ?? PackManagerUtils.assetsDirectory;
  }

  static Future<void> _ensureVoiceDirExists(Directory assetsDirectory) async {
    final dir = Directory('${assetsDirectory.path}/voice');
    if (!dir.existsSync()) {
      await dir.create(recursive: true);
    }
  }

  /// Stores `voiceValue` (base64 or data URL) into `data/voice/` and returns
  /// the file name that should be stored in DB.
  static Future<StoredVoiceAudio?> persistFromBase64({
    required String voiceId,
    required String voiceValue,
    Directory? assetsDirectory,
  }) async {
    final parsed = tryParseBase64Audio(voiceValue);
    if (parsed == null) return null;

    final assetsDir = _assetsDirectory(assetsDirectory);
    await _ensureVoiceDirExists(assetsDir);

    final fileName = _defaultFileName(voiceId: voiceId, ext: parsed.ext);
    final file = File('${assetsDir.path}/voice/$fileName');
    await file.writeAsBytes(parsed.bytes, flush: true);

    return StoredVoiceAudio(
      fileName: fileName,
      contentType: parsed.contentType,
    );
  }

  /// Tries to resolve a local voice file from a DB value.
  ///
  /// Returns the resolved file if it exists, otherwise `null`.
  static Future<ResolvedVoiceAudio?> tryResolveLocalFile({
    required String voiceValue,
    Directory? assetsDirectory,
  }) async {
    final assetsDir = _assetsDirectory(assetsDirectory);
    final v = voiceValue.trim();
    if (v.isEmpty) return null;

    final sanitized = sanitizeVoiceFileName(v);
    if (sanitized == null) return null;

    final file = File('${assetsDir.path}/voice/$sanitized');
    if (!file.existsSync()) return null;

    final bytes = await file.readAsBytes();
    final contentType =
        _detectContentType(bytes) ?? _contentTypeFromFileName(sanitized);

    return ResolvedVoiceAudio(
      fileName: sanitized,
      bytes: bytes,
      contentType: contentType,
    );
  }

  static String _contentTypeFromFileName(String fileName) {
    final lower = fileName.toLowerCase();
    if (lower.endsWith('.mp3')) return 'audio/mpeg';
    if (lower.endsWith('.wav')) return 'audio/wav';
    if (lower.endsWith('.ogg')) return 'audio/ogg';
    if (lower.endsWith('.flac')) return 'audio/flac';
    return 'application/octet-stream';
  }
}

class ParsedVoiceAudio {
  final Uint8List bytes;
  final String contentType;
  final String ext;

  const ParsedVoiceAudio({
    required this.bytes,
    required this.contentType,
    required this.ext,
  });
}

class StoredVoiceAudio {
  final String fileName;
  final String contentType;

  const StoredVoiceAudio({required this.fileName, required this.contentType});
}

class ResolvedVoiceAudio {
  final String fileName;
  final Uint8List bytes;
  final String contentType;

  const ResolvedVoiceAudio({
    required this.fileName,
    required this.bytes,
    required this.contentType,
  });
}