chore(client): 归档发现页 widgets（原型阶段新增目录）

lib/pages/discover/widgets/cover_carousel.dart

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+import 'dart:math' as math;
+
+import 'package:flutter/material.dart';
+import '../../../core/widgets/remote_image.dart';
+
+class CoverItem {
+  const CoverItem({
+    required this.title,
+    required this.subtitle,
+    required this.image,
+    required this.onOpen,
+  });
+
+  final String title;
+  final String subtitle;
+  final String image;
+  final VoidCallback onOpen;
+}
+
+/// Full-bleed posters that turn as faces of a cube. Titles sit on the image.
+class CoverCarousel extends StatefulWidget {
+  const CoverCarousel({super.key, required this.items});
+
+  final List<CoverItem> items;
+
+  @override
+  State<CoverCarousel> createState() => _CoverCarouselState();
+}
+
+class _CoverCarouselState extends State<CoverCarousel>
+    with SingleTickerProviderStateMixin {
+  late final AnimationController _snap;
+  double _page = 0;
+  double _from = 0;
+  double _to = 0;
+  int? _pointer;
+  double _drag = 0;
+  double _dragPage = 0;
+
+  @override
+  void initState() {
+    super.initState();
+    _snap = AnimationController(vsync: this)..addListener(_onSnap);
+  }
+
+  @override
+  void dispose() {
+    _snap.dispose();
+    super.dispose();
+  }
+
+  double get _last => math.max(0, widget.items.length - 1).toDouble();
+
+  void _onSnap() {
+    final t = Curves.easeOutCubic.transform(_snap.value);
+    setState(() => _page = _from + (_to - _from) * t);
+  }
+
+  void _turnTo(double target) {
+    _from = _page;
+    _to = target.clamp(0, _last);
+    _snap.duration = const Duration(milliseconds: 420);
+    _snap.forward(from: 0);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(
+      builder: (context, constraints) {
+        final width = constraints.maxWidth;
+        final height = math.min(width * 0.52, 210).toDouble();
+        return SizedBox(
+          width: double.infinity,
+          height: height,
+          child: _stage(width),
+        );
+      },
+    );
+  }
+
+  Widget _stage(double width) {
+    return Listener(
+      behavior: HitTestBehavior.opaque,
+      onPointerDown: (event) {
+        _snap.stop();
+        _pointer = event.pointer;
+        _drag = 0;
+        _dragPage = _page;
+      },
+      onPointerMove: (event) {
+        if (event.pointer != _pointer) return;
+        _drag += event.delta.dx;
+        setState(() {
+          _page = (_dragPage - _drag / width).clamp(0.0, _last);
+        });
+      },
+      onPointerUp: (event) {
+        if (event.pointer != _pointer) return;
+        _pointer = null;
+        _turnTo(_page.roundToDouble());
+      },
+      onPointerCancel: (event) {
+        if (event.pointer != _pointer) return;
+        _pointer = null;
+        _turnTo(_page.roundToDouble());
+      },
+      child: ClipRect(
+        child: Stack(
+          fit: StackFit.expand,
+          children: [for (final index in _visible) _face(index, width)],
+        ),
+      ),
+    );
+  }
+
+  List<int> get _visible {
+    final first = _page.floor();
+    final indexes = <int>[first, first + 1];
+    indexes.retainWhere((index) => index >= 0 && index < widget.items.length);
+    indexes.sort((a, b) => (b - _page).abs().compareTo((a - _page).abs()));
+    return indexes;
+  }
+
+  Widget _face(int index, double width) {
+    final delta = index - _page;
+    if (delta <= -1 || delta >= 1) return const SizedBox.shrink();
+    final item = widget.items[index];
+    final angle = delta * math.pi / 2;
+    // Push the face out to the cube surface, spin the whole cube on its
+    // vertical center, then bring that center back to the banner.
+    final face = Matrix4.identity()
+      ..translateByDouble(0, 0, -width / 2, 1)
+      ..rotateY(angle)
+      ..translateByDouble(0, 0, width / 2, 1);
+    final transform = Matrix4.identity()
+      ..setEntry(3, 2, 0.0018)
+      ..multiply(face);
+    return Positioned.fill(
+      child: Transform(
+        alignment: Alignment.center,
+        filterQuality: FilterQuality.medium,
+        transform: transform,
+        child: GestureDetector(
+          onTap: () {
+            if ((_page - index).abs() < 0.08) item.onOpen();
+          },
+          child: _poster(item),
+        ),
+      ),
+    );
+  }
+
+  Widget _poster(CoverItem item) {
+    return Stack(
+      fit: StackFit.expand,
+      children: [
+        RemoteImage(item.image),
+        const DecoratedBox(
+          decoration: BoxDecoration(
+            gradient: LinearGradient(
+              begin: Alignment.topCenter,
+              end: Alignment.bottomCenter,
+              colors: [Color(0x00000000), Color(0x00000000), Color(0xE6000000)],
+              stops: [0, 0.5, 1],
+            ),
+          ),
+        ),
+        Positioned(
+          left: 20,
+          right: 20,
+          bottom: 22,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Text(
+                item.title,
+                maxLines: 2,
+                overflow: TextOverflow.ellipsis,
+                style: const TextStyle(
+                  color: Colors.white,
+                  fontSize: 20,
+                  fontWeight: FontWeight.w600,
+                  height: 1.15,
+                  shadows: [Shadow(blurRadius: 12, color: Colors.black)],
+                ),
+              ),
+              const SizedBox(height: 6),
+              Text(
+                item.subtitle,
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+                style: const TextStyle(
+                  color: Color(0xF2FFFFFF),
+                  fontSize: 14,
+                  fontWeight: FontWeight.w400,
+                  height: 1.2,
+                  shadows: [Shadow(blurRadius: 8, color: Colors.black)],
+                ),
+              ),
+            ],
+          ),
+        ),
+      ],
+    );
+  }
+}