395 lines
11 KiB
Dart
395 lines
11 KiB
Dart
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import 'dart:convert';
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import 'package:dio/dio.dart';
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import 'package:flutter/foundation.dart';
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import '../../shared/utils/app_logger.dart';
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import 'embedded_subtitle_cues.dart';
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const _tag = 'ExternalSubtitleLoader';
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const _backgroundParseThresholdBytes = 256 * 1024;
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class ExternalSubtitleLoadException implements Exception {
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final String message;
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final Object? cause;
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const ExternalSubtitleLoadException(this.message, [this.cause]);
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@override
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String toString() =>
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'ExternalSubtitleLoadException: $message'
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'${cause != null ? ' ($cause)' : ''}';
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}
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class ExternalSubtitleLoader {
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final Dio _dio;
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final Map<String, List<TimedSubtitle>> _cacheByUrl = {};
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final Map<String, Future<List<TimedSubtitle>>> _inflightByUrl = {};
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ExternalSubtitleLoader({Dio? dio})
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: _dio =
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dio ??
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Dio(
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BaseOptions(
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connectTimeout: const Duration(seconds: 10),
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receiveTimeout: const Duration(seconds: 20),
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responseType: ResponseType.bytes,
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),
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);
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Future<List<TimedSubtitle>> load(
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String url, {
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Map<String, String>? headers,
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Duration? receiveTimeout,
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}) {
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final cached = _cacheByUrl[url];
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if (cached != null) return Future.value(cached);
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final inflight = _inflightByUrl[url];
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if (inflight != null) return inflight;
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final future = _download(url, headers, receiveTimeout).whenComplete(() {
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_inflightByUrl.remove(url);
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});
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_inflightByUrl[url] = future;
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return future;
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}
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Future<List<TimedSubtitle>> _download(
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String url,
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Map<String, String>? headers,
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Duration? receiveTimeout,
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) async {
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List<int> bytes;
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try {
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final response = await _dio.get<List<int>>(
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url,
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options: Options(
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headers: headers,
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responseType: ResponseType.bytes,
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receiveTimeout: receiveTimeout,
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),
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);
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bytes = response.data ?? const [];
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} on DioException catch (error) {
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AppLogger.warn(
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_tag,
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'download failed url=$url status=${error.response?.statusCode} '
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'type=${error.type}',
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);
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throw ExternalSubtitleLoadException('外挂字幕下载失败', error);
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}
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if (bytes.isEmpty) {
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AppLogger.warn(_tag, 'download returned empty body url=$url');
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throw const ExternalSubtitleLoadException('外挂字幕内容为空');
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}
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final content = _decodeText(bytes);
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final cues = bytes.length >= _backgroundParseThresholdBytes
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? await compute(parseSubtitleContent, content)
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: parseSubtitleContent(content);
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if (cues.isEmpty) {
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AppLogger.warn(
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_tag,
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'parse produced no cues url=$url bytes=${bytes.length}',
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);
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throw const ExternalSubtitleLoadException('外挂字幕解析结果为空');
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}
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_cacheByUrl[url] = cues;
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AppLogger.debug(_tag, 'loaded url=$url cues=${cues.length}');
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return cues;
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}
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void clear() {
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_cacheByUrl.clear();
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_inflightByUrl.clear();
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}
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static String _decodeText(List<int> bytes) {
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var start = 0;
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if (bytes.length >= 3 &&
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bytes[0] == 0xEF &&
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bytes[1] == 0xBB &&
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bytes[2] == 0xBF) {
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start = 3;
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}
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final body = start == 0 ? bytes : bytes.sublist(start);
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try {
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return utf8.decode(body);
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} on FormatException {
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return latin1.decode(body);
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}
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}
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static List<TimedSubtitle> parseSubtitleContent(String content) {
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final normalized = content.replaceAll('\r\n', '\n').replaceAll('\r', '\n');
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final trimmed = normalized.trimLeft();
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if (trimmed.startsWith('WEBVTT')) {
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return _parseVtt(normalized);
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}
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if (trimmed.startsWith('[Script Info]') ||
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normalized.contains('\nDialogue:') ||
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trimmed.startsWith('Dialogue:')) {
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return _parseAss(normalized);
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}
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return _parseSrt(normalized);
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}
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static final RegExp _srtTimeLine = RegExp(
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r'(\d{1,2}):(\d{2}):(\d{2})[,.](\d{1,3})\s*-->\s*(\d{1,2}):(\d{2}):(\d{2})[,.](\d{1,3})',
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);
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static List<TimedSubtitle> _parseSrt(String content) {
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final cues = <TimedSubtitle>[];
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final blocks = content.split(RegExp(r'\n{2,}'));
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for (final block in blocks) {
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final lines = block
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.split('\n')
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.where((line) => line.trim().isNotEmpty)
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.toList();
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if (lines.isEmpty) continue;
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var timeLineIndex = -1;
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RegExpMatch? timeMatch;
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for (var i = 0; i < lines.length; i++) {
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timeMatch = _srtTimeLine.firstMatch(lines[i]);
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if (timeMatch != null) {
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timeLineIndex = i;
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break;
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}
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}
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if (timeMatch == null) continue;
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final textLines = lines
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.sublist(timeLineIndex + 1)
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.map(_stripHtmlTags)
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.where((line) => line.trim().isNotEmpty)
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.toList();
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if (textLines.isEmpty) continue;
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cues.add(
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TimedSubtitle(
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start: _timeFromMatch(timeMatch, 1),
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end: _timeFromMatch(timeMatch, 5),
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text: textLines.join('\n'),
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),
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);
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}
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return _sortAndValidate(cues);
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}
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static List<TimedSubtitle> _parseVtt(String content) {
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final vttTimeLine = RegExp(
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r'(?:(\d{1,2}):)?(\d{2}):(\d{2})\.(\d{3})\s*-->\s*(?:(\d{1,2}):)?(\d{2}):(\d{2})\.(\d{3})',
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);
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final cues = <TimedSubtitle>[];
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final blocks = content.split(RegExp(r'\n{2,}'));
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for (final block in blocks) {
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final lines = block
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.split('\n')
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.where((line) => line.trim().isNotEmpty)
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.toList();
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if (lines.isEmpty) continue;
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final first = lines.first.trim();
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if (first.startsWith('WEBVTT') ||
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first.startsWith('NOTE') ||
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first.startsWith('STYLE') ||
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first.startsWith('REGION')) {
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continue;
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}
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var timeLineIndex = -1;
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RegExpMatch? timeMatch;
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for (var i = 0; i < lines.length; i++) {
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timeMatch = vttTimeLine.firstMatch(lines[i]);
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if (timeMatch != null) {
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timeLineIndex = i;
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break;
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}
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}
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if (timeMatch == null) continue;
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final textLines = lines
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.sublist(timeLineIndex + 1)
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.map(_stripHtmlTags)
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.where((line) => line.trim().isNotEmpty)
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.toList();
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if (textLines.isEmpty) continue;
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cues.add(
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TimedSubtitle(
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start: _vttTimeFromMatch(timeMatch, 1),
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end: _vttTimeFromMatch(timeMatch, 5),
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text: textLines.join('\n'),
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),
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);
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}
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return _sortAndValidate(cues);
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}
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static final RegExp _assTime = RegExp(r'^(\d+):(\d{2}):(\d{2})\.(\d{2})$');
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static List<TimedSubtitle> _parseAss(String content) {
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final cues = <TimedSubtitle>[];
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var startFieldIndex = 1;
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var endFieldIndex = 2;
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var textFieldIndex = 9;
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for (final rawLine in content.split('\n')) {
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final line = rawLine.trim();
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if (line.startsWith('Format:')) {
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final fields = line
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.substring('Format:'.length)
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.split(',')
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.map((field) => field.trim().toLowerCase())
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.toList();
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final start = fields.indexOf('start');
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final end = fields.indexOf('end');
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final text = fields.indexOf('text');
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if (start >= 0 && end >= 0 && text >= 0) {
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startFieldIndex = start;
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endFieldIndex = end;
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textFieldIndex = text;
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}
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continue;
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}
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if (!line.startsWith('Dialogue:')) continue;
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final payload = line.substring('Dialogue:'.length).trim();
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final parts = payload.split(',');
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if (parts.length <= textFieldIndex) continue;
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final startRaw = parts[startFieldIndex].trim();
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final endRaw = parts[endFieldIndex].trim();
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final textRaw = parts.sublist(textFieldIndex).join(',');
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final start = _parseAssTime(startRaw);
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final end = _parseAssTime(endRaw);
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if (start == null || end == null) continue;
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final text = _cleanAssText(textRaw);
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if (text.isEmpty) continue;
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cues.add(TimedSubtitle(start: start, end: end, text: text));
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}
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return _sortAndValidate(cues);
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}
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static Duration? _parseAssTime(String raw) {
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final match = _assTime.firstMatch(raw);
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if (match == null) return null;
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return Duration(
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hours: int.parse(match.group(1)!),
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minutes: int.parse(match.group(2)!),
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seconds: int.parse(match.group(3)!),
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milliseconds: int.parse(match.group(4)!) * 10,
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);
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}
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static String _cleanAssText(String raw) {
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var text = raw.replaceAll(RegExp(r'\{[^}]*\}'), '');
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text = text
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.replaceAll(r'\N', '\n')
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.replaceAll(r'\n', '\n')
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.replaceAll(r'\h', ' ');
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return text
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.split('\n')
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.map((line) => line.trim())
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.where((line) => line.isNotEmpty)
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.join('\n')
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.trim();
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}
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static String _stripHtmlTags(String line) =>
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line.replaceAll(RegExp(r'</?[^>]+>'), '');
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static Duration _timeFromMatch(RegExpMatch match, int groupOffset) {
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final millisRaw = match.group(groupOffset + 3)!;
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final millis = int.parse(millisRaw.padRight(3, '0'));
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return Duration(
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hours: int.parse(match.group(groupOffset)!),
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minutes: int.parse(match.group(groupOffset + 1)!),
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seconds: int.parse(match.group(groupOffset + 2)!),
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milliseconds: millis,
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);
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}
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static Duration _vttTimeFromMatch(RegExpMatch match, int groupOffset) {
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return Duration(
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hours: int.parse(match.group(groupOffset) ?? '0'),
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minutes: int.parse(match.group(groupOffset + 1)!),
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seconds: int.parse(match.group(groupOffset + 2)!),
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milliseconds: int.parse(match.group(groupOffset + 3)!),
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);
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}
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static List<TimedSubtitle> _sortAndValidate(List<TimedSubtitle> cues) {
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final valid = cues.where((cue) => cue.end >= cue.start).toList()
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..sort((a, b) => a.start.compareTo(b.start));
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return valid;
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}
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}
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class SubtitleCueSource {
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final List<TimedSubtitle> _cues;
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final List<Duration> _prefixMaximumEnd;
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SubtitleCueSource(List<TimedSubtitle> sortedCues)
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: _cues = sortedCues,
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_prefixMaximumEnd = _buildPrefixMaximumEnd(sortedCues);
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bool get isEmpty => _cues.isEmpty;
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List<String> textAt(Duration position) {
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final firstPossibleIndex = _firstCueThatMayOverlap(position);
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if (firstPossibleIndex >= _cues.length) return const [];
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final lines = <String>[];
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for (
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var cueIndex = firstPossibleIndex;
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cueIndex < _cues.length;
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cueIndex++
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) {
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final cue = _cues[cueIndex];
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if (position < cue.start) break;
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if (position <= cue.end) lines.addAll(cue.text.split('\n'));
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}
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return lines;
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}
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int _firstCueThatMayOverlap(Duration position) {
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var lowerBound = 0;
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var upperBound = _prefixMaximumEnd.length;
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while (lowerBound < upperBound) {
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final middleIndex = (lowerBound + upperBound) >> 1;
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if (_prefixMaximumEnd[middleIndex] < position) {
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lowerBound = middleIndex + 1;
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} else {
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upperBound = middleIndex;
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}
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}
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return lowerBound;
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}
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static List<Duration> _buildPrefixMaximumEnd(List<TimedSubtitle> sortedCues) {
|
||
|
|
final prefixMaximumEnd = <Duration>[];
|
||
|
|
var maximumEnd = Duration.zero;
|
||
|
|
for (final cue in sortedCues) {
|
||
|
|
if (cue.end > maximumEnd) maximumEnd = cue.end;
|
||
|
|
prefixMaximumEnd.add(maximumEnd);
|
||
|
|
}
|
||
|
|
return prefixMaximumEnd;
|
||
|
|
}
|
||
|
|
}
|