frosty/lib/apis/twitch_ad_solutions.dart

import 'package:flutter/foundation.dart';
import 'package:frosty/apis/twitch_gql_api.dart';
import 'package:frosty/models/playback_access_token.dart';

/// Dart-side port of the [TwitchAdSolutions vaft](https://github.com/pixeltris/TwitchAdSolutions)
/// strategy for Frosty's native HLS player.
///
/// Browser vaft hooks `Worker`/`fetch` to rewrite playlists. Here we instead:
/// 1. Request playback tokens with a non-`site` [forceAccessTokenPlayerType]
///    (vaft's `ForceAccessTokenPlayerType`).
/// 2. When stitched ads still appear, try [backupPlayerTypes] until a playlist
///    without the ad signifier is found, then hand that Usher URL to the player.
class TwitchAdSolutions {
  TwitchAdSolutions._();

  /// Matches vaft `AdSignifier` — Twitch marks ad pods with this in `#EXT-X-DATERANGE`.
  static const adSignifier = 'stitched';

  /// vaft `ForceAccessTokenPlayerType` — used for the primary stream when
  /// ad blocking is enabled.
  static const forceAccessTokenPlayerType = 'popout';

  /// vaft `BackupPlayerTypes` order when the primary playlist still has ads.
  static const backupPlayerTypes = <String>[
    'embed',
    'popout',
    'autoplay',
  ];

  /// vaft `FallbackPlayerType` when every backup still carries ads.
  static const fallbackPlayerType = 'embed';

  /// GQL `platform` for a given player type (vaft uses `android` for autoplay).
  static String platformForPlayerType(String playerType) =>
      playerType == 'autoplay' ? 'android' : 'web';

  static bool playlistContainsAds(String playlistText) =>
      playlistText.contains(adSignifier);

  /// True when [text] looks like a midroll (vaft midroll banner path).
  static bool playlistIsMidroll(String playlistText) =>
      playlistText.contains('"MIDROLL"') ||
      playlistText.contains('"midroll"') ||
      playlistText.contains("MIDROLL");
}

/// Resolves Usher HLS URLs using TwitchAdSolutions player-type strategy.
class TwitchAdFreePlayback {
  TwitchAdFreePlayback(this._gql);

  final TwitchGqlApi _gql;

  /// Primary URL when adblock is on: force [TwitchAdSolutions.forceAccessTokenPlayerType].
  Future<({String url, PlaybackAccessToken token, String playerType})>
  resolvePrimary({
    required String login,
    String? authToken,
  }) {
    return _resolveForPlayerType(
      login: login,
      authToken: authToken,
      playerType: TwitchAdSolutions.forceAccessTokenPlayerType,
      requireAdFree: false,
    );
  }

  /// Walks [TwitchAdSolutions.backupPlayerTypes] for a playlist without ads.
  /// Falls back to [TwitchAdSolutions.fallbackPlayerType] even if ads remain.
  Future<({String url, PlaybackAccessToken token, String playerType})>
  resolveBackup({
    required String login,
    String? authToken,
  }) async {
    for (final playerType in TwitchAdSolutions.backupPlayerTypes) {
      try {
        final resolved = await _resolveForPlayerType(
          login: login,
          authToken: authToken,
          playerType: playerType,
          requireAdFree: true,
        );
        debugPrint(
          'TwitchAdFreePlayback: backup OK playerType=$playerType',
        );
        return resolved;
      } catch (e) {
        debugPrint(
          'TwitchAdFreePlayback: backup playerType=$playerType failed: $e',
        );
      }
    }

    debugPrint(
      'TwitchAdFreePlayback: all backups had ads; using fallback '
      '${TwitchAdSolutions.fallbackPlayerType}',
    );
    return _resolveForPlayerType(
      login: login,
      authToken: authToken,
      playerType: TwitchAdSolutions.fallbackPlayerType,
      requireAdFree: false,
    );
  }

  Future<({String url, PlaybackAccessToken token, String playerType})>
  _resolveForPlayerType({
    required String login,
    String? authToken,
    required String playerType,
    required bool requireAdFree,
  }) async {
    final token = await _gql.getPlaybackAccessToken(
      login: login,
      authToken: authToken,
      playerType: playerType,
      platform: TwitchAdSolutions.platformForPlayerType(playerType),
    );
    final url = _gql.buildHlsUrl(login: login, token: token);

    if (requireAdFree) {
      final hasAds = await _multivariantHasAds(url);
      if (hasAds) {
        throw StateError('Playlist for playerType=$playerType still has ads');
      }
    }

    return (url: url, token: token, playerType: playerType);
  }

  /// Fetches the multivariant playlist and samples the first media variant for
  /// the ad signifier (same idea as vaft probing backup encodings).
  Future<bool> _multivariantHasAds(String hlsUrl) async {
    final master = await _gql.fetchPlaylistText(hlsUrl);
    final mediaUrl = firstMediaPlaylistUrl(master, baseUrl: hlsUrl);
    if (mediaUrl == null) {
      // Can't verify — treat as ad-free so we don't reject a usable stream.
      return false;
    }
    final media = await _gql.fetchPlaylistText(mediaUrl);
    return TwitchAdSolutions.playlistContainsAds(media);
  }

  /// First `.m3u8` URI in a multivariant playlist, resolved against [baseUrl].
  @visibleForTesting
  static String? firstMediaPlaylistUrl(
    String masterPlaylist, {
    required String baseUrl,
  }) {
    final lines = masterPlaylist.replaceAll('\r', '').split('\n');
    for (final raw in lines) {
      final line = raw.trim();
      if (line.isEmpty || line.startsWith('#')) continue;
      if (!line.contains('.m3u8')) continue;
      return Uri.parse(baseUrl).resolve(line).toString();
    }
    return null;
  }
}

/// Tiny blank MP4 (same payload vaft serves for stripped ad segments). Exposed
/// for tests / future local playlist rewriting; not required for URL-swap mode.
const twitchAdSolutionsBlankSegmentDataUri =
    'data:video/mp4;base64,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';