ReelShort/lib/pages/player/widgets/player_opening_frame.dart

// Author: fruit.com.cn

import 'dart:async';

import 'package:flutter/material.dart';

import '../../../core/config/app_config.dart';
import '../../../core/data/services/sprite_thumbnail_axis.dart';
import '../../../core/theme/app_colors.dart';
import '../../../core/widgets/remote_image.dart';
import 'scrub_preview_card.dart';

enum PlayerOpeningFallback { handoff, poster, thumbnails, black }

PlayerOpeningFallback playerOpeningFallback({
  String? posterUrl,
  String? thumbnailsUrl,
}) {
  if (posterUrl?.trim().isNotEmpty ?? false) {
    return PlayerOpeningFallback.poster;
  }
  if (thumbnailsUrl?.trim().isNotEmpty ?? false) {
    return PlayerOpeningFallback.thumbnails;
  }
  return PlayerOpeningFallback.black;
}

/// 当前集首帧在视频纹理未就绪时占位；空地址交还纯黑底。
Widget? playerOpeningFrame(
  String? thumbnailsUrl, {
  String? posterUrl,
  required SpriteThumbnailAxisSource spriteSource,
  BoxFit fit = BoxFit.cover,
}) {
  final thumbnails = thumbnailsUrl?.trim() ?? '';
  final poster = posterUrl?.trim() ?? '';
  if (playerOpeningFallback(posterUrl: poster, thumbnailsUrl: thumbnails) ==
      PlayerOpeningFallback.black) {
    return null;
  }
  return PlayerOpeningFrame(
    thumbnailsUrl: thumbnails,
    posterUrl: poster,
    spriteSource: spriteSource,
    fit: fit,
  );
}

/// 与视频共用全屏父约束和 BoxFit，切换时保持相同可见区域。
class PlayerOpeningFrame extends StatefulWidget {
  const PlayerOpeningFrame({
    super.key,
    required this.thumbnailsUrl,
    required this.spriteSource,
    this.posterUrl,
    this.fit = BoxFit.cover,
  });

  /// 当前视频原始分辨率首帧地址，优先于雪碧图。
  final String? posterUrl;

  /// 当前视频雪碧图 WebVTT 地址。
  final String thumbnailsUrl;

  /// 进度条拖动预览共用的雪碧图时间轴与解码缓存。
  final SpriteThumbnailAxisSource spriteSource;

  /// 必须与同页视频层使用相同适配规则。
  final BoxFit fit;

  @override
  State<PlayerOpeningFrame> createState() => _PlayerOpeningFrameState();
}

class _PlayerOpeningFrameState extends State<PlayerOpeningFrame> {
  bool _posterFailed = false;

  @override
  void initState() {
    super.initState();
    widget.spriteSource.addListener(_handleSpriteChanged);
    _prepareSpriteIfNeeded();
  }

  @override
  void didUpdateWidget(covariant PlayerOpeningFrame oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.posterUrl != widget.posterUrl) {
      _posterFailed = false;
    }
    if (oldWidget.spriteSource != widget.spriteSource) {
      oldWidget.spriteSource.removeListener(_handleSpriteChanged);
      widget.spriteSource.addListener(_handleSpriteChanged);
      _prepareSpriteIfNeeded();
    }
    if (oldWidget.posterUrl != widget.posterUrl ||
        oldWidget.thumbnailsUrl != widget.thumbnailsUrl) {
      _prepareSpriteIfNeeded();
    }
  }

  @override
  void dispose() {
    widget.spriteSource.removeListener(_handleSpriteChanged);
    super.dispose();
  }

  void _handleSpriteChanged() {
    if (mounted) setState(() {});
  }

  bool get _hasPoster =>
      !_posterFailed && (widget.posterUrl?.trim().isNotEmpty ?? false);

  void _prepareSpriteIfNeeded() {
    if (_hasPoster || widget.thumbnailsUrl.trim().isEmpty) return;
    unawaited(
      widget.spriteSource.prepareAt(widget.thumbnailsUrl, Duration.zero),
    );
  }

  Widget _handlePosterError() {
    if (!_posterFailed) {
      WidgetsBinding.instance.addPostFrameCallback((_) {
        if (!mounted || _posterFailed) return;
        setState(() => _posterFailed = true);
        _prepareSpriteIfNeeded();
      });
    }
    return _spriteOrBlack();
  }

  Widget _spriteOrBlack() {
    final frame = widget.spriteSource.cachedFrameAt(
      widget.thumbnailsUrl,
      Duration.zero,
    );
    if (frame == null) return const SizedBox.expand();
    return SpriteCropPreview(
      key: const Key('player-opening-sprite'),
      image: frame.image,
      sourceRect: frame.sourceRect,
      fit: widget.fit,
    );
  }

  @override
  Widget build(BuildContext context) => Stack(
    fit: StackFit.expand,
    children: [
      const ColoredBox(color: AppColors.mediaBlack),
      if (_hasPoster)
        LayoutBuilder(
          builder: (context, constraints) {
            final pixelRatio = MediaQuery.devicePixelRatioOf(context);
            return Image.network(
              AppConfig.mediaUrl(widget.posterUrl!.trim()),
              key: const Key('player-opening-poster'),
              fit: widget.fit,
              cacheWidth: resolveImageDecodePixels(
                constraints.maxWidth,
                pixelRatio,
              ),
              cacheHeight: resolveImageDecodePixels(
                constraints.maxHeight,
                pixelRatio,
              ),
              gaplessPlayback: true,
              errorBuilder: (_, _, _) => _handlePosterError(),
            );
          },
        )
      else
        _spriteOrBlack(),
    ],
  );
}