SpotiFLAC-Mobile/lib/services/automix_analyzer.dart

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

import 'package:ffmpeg_kit_flutter_new_full/ffmpeg_kit.dart';
import 'package:ffmpeg_kit_flutter_new_full/return_code.dart';
import 'package:flutter/foundation.dart';
import 'package:path_provider/path_provider.dart';
import 'package:spotiflac_android/services/audio_analysis_jobs.dart';
import 'package:spotiflac_android/services/automix_analysis.dart';

/// Only short head/tail windows are decoded. Summaries are bounded in memory;
/// raw PCM is deleted immediately and is never added to the user's library.
class AutoMixAnalyzer {
  static const windowSeconds = 24.0;
  final _cache = <String, AutoMixBeatGrid>{};
  final _jobs = AudioAnalysisJobs<bool>(
    start: (arguments) async {
      final done = Completer<bool>();
      final session = await FFmpegKit.executeWithArgumentsAsync(arguments, (
        session,
      ) async {
        final success = ReturnCode.isSuccess(await session.getReturnCode());
        if (!done.isCompleted) done.complete(success);
      });
      final id = session.getSessionId();
      if (id == null) throw StateError('AutoMix analysis session has no ID');
      final timeout = Timer(const Duration(seconds: 20), () {
        unawaited(FFmpegKit.cancel(id));
      });
      return (id: id, completed: done.future.whenComplete(timeout.cancel));
    },
    cancel: FFmpegKit.cancel,
  );
  int _generation = 0;

  void cancel() {
    _generation++;
    _jobs.invalidate();
  }

  void dispose() {
    _generation++;
    _jobs.dispose();
    _cache.clear();
  }

  Future<AutoMixBeatGrid?> analyze(String path, {double offset = 0}) async {
    final generation = _generation;
    Directory? work;
    try {
      final stat = await File(path).stat();
      if (stat.type != FileSystemEntityType.file) return null;
      final key =
          '$path:${stat.size}:${stat.modified.microsecondsSinceEpoch}:$offset';
      final cached = _cache.remove(key);
      if (cached != null) {
        _cache[key] = cached;
        return cached;
      }
      if (generation != _generation) return null;
      final temp = await getTemporaryDirectory();
      work = await Directory(temp.path).createTemp('automix-');
      final output = File('${work.path}/window.pcm');
      final success = await _jobs.run([
        '-hide_banner',
        '-loglevel',
        'error',
        '-nostdin',
        '-y',
        '-threads',
        '1',
        '-filter_threads',
        '1',
        '-ss',
        offset.toStringAsFixed(6),
        '-i',
        path,
        '-t',
        '$windowSeconds',
        '-vn',
        '-sn',
        '-dn',
        '-ac',
        '1',
        '-ar',
        '11025',
        '-c:a',
        'pcm_s16le',
        '-f',
        's16le',
        output.path,
      ]);
      if (!success || generation != _generation || !await output.exists()) {
        return null;
      }
      if (await output.length() > 11025 * 2 * 25) return null;
      final grid = await compute(analyzeAutoMixPcm, await output.readAsBytes());
      if (generation != _generation) return null;
      _cache[key] = grid;
      while (_cache.length > 16) {
        _cache.remove(_cache.keys.first);
      }
      return grid;
    } on AudioAnalysisCancelled {
      return null;
    } on Object {
      // Unsupported/corrupt input must not interrupt ordinary playback.
      return null;
    } finally {
      if (work != null && await work.exists()) {
        await work.delete(recursive: true);
      }
    }
  }
}