feat: implement collections feature with screens for viewing, managing, and creating collections

.gitignore

@@ -45,3 +45,4 @@ app.*.map.json
 /android/app/release
 
 TPB.md
+*sql

lib/screens/collections_screen.dart

@@ -0,0 +1,409 @@
+import 'package:flutter/material.dart';
+import '../main.dart';
+import '../services/collection_service.dart';
+import '../theme/app_colors.dart';
+import 'garage_screen.dart';
+import 'manage_collection_screen.dart';
+
+/// Lists all collections the current user is a member of.
+class CollectionsScreen extends StatefulWidget {
+  const CollectionsScreen({super.key});
+
+  @override
+  State<CollectionsScreen> createState() => CollectionsScreenState();
+}
+
+class CollectionsScreenState extends State<CollectionsScreen> {
+  List<Collection> _collections = [];
+  bool _isLoading = true;
+  String? _error;
+
+  @override
+  void initState() {
+    super.initState();
+    _load();
+  }
+
+  /// Public so other tabs can trigger a refresh.
+  void refresh() => _load();
+
+  Future<void> _load() async {
+    setState(() {
+      _isLoading = true;
+      _error = null;
+    });
+
+    try {
+      final list = await CollectionService.getMyCollections();
+      if (!mounted) return;
+      setState(() {
+        _collections = list;
+        _isLoading = false;
+      });
+    } catch (e) {
+      if (!mounted) return;
+      setState(() {
+        _error = e.toString();
+        _isLoading = false;
+      });
+    }
+  }
+
+  Future<void> _createCollection() async {
+    final nameCtrl = TextEditingController();
+    final descCtrl = TextEditingController();
+
+    final result = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        icon: Container(
+          padding: const EdgeInsets.all(12),
+          decoration: const BoxDecoration(
+            gradient: AppColors.brandGradient,
+            shape: BoxShape.circle,
+          ),
+          child: const Icon(Icons.add, color: Colors.white, size: 28),
+        ),
+        title: const Text('New Collection'),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            TextField(
+              controller: nameCtrl,
+              autofocus: true,
+              decoration: const InputDecoration(
+                labelText: 'Name',
+                hintText: 'e.g. Hot Wheels, Matchbox…',
+              ),
+            ),
+            const SizedBox(height: 12),
+            TextField(
+              controller: descCtrl,
+              decoration: const InputDecoration(
+                labelText: 'Description (optional)',
+                hintText: 'What is this collection for?',
+              ),
+            ),
+          ],
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () {
+              if (nameCtrl.text.trim().isEmpty) return;
+              Navigator.pop(context, true);
+            },
+            child: const Text('Create'),
+          ),
+        ],
+      ),
+    );
+
+    if (result != true) return;
+
+    try {
+      await CollectionService.create(
+        name: nameCtrl.text.trim(),
+        description: descCtrl.text.trim(),
+      );
+      showGlobalSnackBar('Collection created!');
+      _load();
+    } catch (e) {
+      showGlobalSnackBar('Failed: $e', isError: true);
+    }
+  }
+
+  void _openCollection(Collection c) {
+    navigatorKey.currentState!.push(
+      MaterialPageRoute(
+        builder: (_) => GarageScreen(
+          collectionId: c.id,
+          collectionName: c.name,
+          isOwner: c.isOwner,
+        ),
+      ),
+    ).then((_) => _load()); // refresh counts when coming back
+  }
+
+  void _manageCollection(Collection c) {
+    navigatorKey.currentState!.push(
+      MaterialPageRoute(
+        builder: (_) => ManageCollectionScreen(collection: c),
+      ),
+    ).then((_) => _load());
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: CustomScrollView(
+        slivers: [
+          // ── Header ──
+          SliverAppBar(
+            expandedHeight: 140,
+            pinned: true,
+            flexibleSpace: FlexibleSpaceBar(
+              titlePadding: const EdgeInsets.only(left: 20, bottom: 16),
+              title: Text(
+                'Collections',
+                style: TextStyle(
+                  fontFamily: 'Poppins',
+                  fontWeight: FontWeight.w700,
+                  fontSize: 22,
+                  color: Colors.white,
+                  shadows: [
+                    Shadow(
+                      color: Colors.black.withValues(alpha: 0.3),
+                      blurRadius: 4,
+                    ),
+                  ],
+                ),
+              ),
+              background: Container(
+                decoration: const BoxDecoration(
+                  gradient: AppColors.brandGradient,
+                ),
+                child: Align(
+                  alignment: Alignment.centerRight,
+                  child: Padding(
+                    padding: const EdgeInsets.only(right: 24),
+                    child: Icon(
+                      Icons.collections_bookmark,
+                      size: 72,
+                      color: Colors.white.withValues(alpha: 0.15),
+                    ),
+                  ),
+                ),
+              ),
+            ),
+          ),
+
+          // ── Content ──
+          if (_isLoading)
+            const SliverFillRemaining(
+              child: Center(child: CircularProgressIndicator()),
+            )
+          else if (_error != null)
+            SliverFillRemaining(
+              child: Center(
+                child: Column(
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    const Icon(Icons.error_outline,
+                        size: 56, color: AppColors.error),
+                    const SizedBox(height: 16),
+                    Text(_error!,
+                        textAlign: TextAlign.center,
+                        style:
+                            const TextStyle(color: AppColors.textSecondary)),
+                    const SizedBox(height: 16),
+                    ElevatedButton.icon(
+                      onPressed: _load,
+                      icon: const Icon(Icons.refresh),
+                      label: const Text('Retry'),
+                    ),
+                  ],
+                ),
+              ),
+            )
+          else if (_collections.isEmpty)
+            SliverFillRemaining(
+              child: Center(
+                child: Padding(
+                  padding: const EdgeInsets.all(40),
+                  child: Column(
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      Icon(Icons.collections_bookmark_outlined,
+                          size: 64, color: AppColors.textHint),
+                      const SizedBox(height: 16),
+                      const Text(
+                        'No collections yet',
+                        style: TextStyle(
+                          fontSize: 18,
+                          fontWeight: FontWeight.w600,
+                          color: AppColors.textSecondary,
+                        ),
+                      ),
+                      const SizedBox(height: 8),
+                      const Text(
+                        'Create your first collection to start tracking!',
+                        textAlign: TextAlign.center,
+                        style: TextStyle(color: AppColors.textHint),
+                      ),
+                      const SizedBox(height: 24),
+                      ElevatedButton.icon(
+                        onPressed: _createCollection,
+                        icon: const Icon(Icons.add),
+                        label: const Text('Create Collection'),
+                      ),
+                    ],
+                  ),
+                ),
+              ),
+            )
+          else
+            SliverPadding(
+              padding: const EdgeInsets.fromLTRB(16, 16, 16, 100),
+              sliver: SliverList(
+                delegate: SliverChildBuilderDelegate(
+                  (context, index) {
+                    final c = _collections[index];
+                    return _CollectionCard(
+                      collection: c,
+                      onTap: () => _openCollection(c),
+                      onManage: () => _manageCollection(c),
+                    );
+                  },
+                  childCount: _collections.length,
+                ),
+              ),
+            ),
+        ],
+      ),
+      floatingActionButton: _collections.isNotEmpty
+          ? FloatingActionButton(
+              onPressed: _createCollection,
+              child: const Icon(Icons.add),
+            )
+          : null,
+    );
+  }
+}
+
+// ── Collection Card ──────────────────────────────────────────────────
+
+class _CollectionCard extends StatelessWidget {
+  final Collection collection;
+  final VoidCallback onTap;
+  final VoidCallback onManage;
+
+  const _CollectionCard({
+    required this.collection,
+    required this.onTap,
+    required this.onManage,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final c = collection;
+    return Card(
+      margin: const EdgeInsets.only(bottom: 12),
+      child: InkWell(
+        onTap: onTap,
+        borderRadius: BorderRadius.circular(16),
+        child: Padding(
+          padding: const EdgeInsets.all(16),
+          child: Row(
+            children: [
+              // Icon
+              Container(
+                width: 56,
+                height: 56,
+                decoration: BoxDecoration(
+                  gradient: c.isOwner
+                      ? AppColors.brandGradient
+                      : const LinearGradient(
+                          colors: [AppColors.navy, AppColors.navyLight],
+                        ),
+                  borderRadius: BorderRadius.circular(14),
+                ),
+                child: Icon(
+                  c.isOwner
+                      ? Icons.collections_bookmark
+                      : Icons.group,
+                  color: Colors.white,
+                  size: 28,
+                ),
+              ),
+              const SizedBox(width: 16),
+
+              // Info
+              Expanded(
+                child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  children: [
+                    Text(
+                      c.name,
+                      style: const TextStyle(
+                        fontSize: 17,
+                        fontWeight: FontWeight.w600,
+                      ),
+                    ),
+                    const SizedBox(height: 4),
+                    Row(
+                      children: [
+                        _MiniStat(
+                            icon: Icons.directions_car,
+                            value: '${c.itemCount}'),
+                        const SizedBox(width: 16),
+                        _MiniStat(
+                            icon: Icons.people,
+                            value: '${c.memberCount}'),
+                        const SizedBox(width: 16),
+                        Container(
+                          padding: const EdgeInsets.symmetric(
+                              horizontal: 8, vertical: 2),
+                          decoration: BoxDecoration(
+                            color: c.isOwner
+                                ? AppColors.orange.withValues(alpha: 0.15)
+                                : AppColors.navy.withValues(alpha: 0.1),
+                            borderRadius: BorderRadius.circular(6),
+                          ),
+                          child: Text(
+                            c.isOwner ? 'Owner' : 'Member',
+                            style: TextStyle(
+                              fontSize: 11,
+                              fontWeight: FontWeight.w600,
+                              color: c.isOwner
+                                  ? AppColors.orange
+                                  : AppColors.navy,
+                            ),
+                          ),
+                        ),
+                      ],
+                    ),
+                  ],
+                ),
+              ),
+
+              // Manage button
+              IconButton(
+                icon: const Icon(Icons.settings_outlined,
+                    color: AppColors.textHint),
+                onPressed: onManage,
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+class _MiniStat extends StatelessWidget {
+  final IconData icon;
+  final String value;
+  const _MiniStat({required this.icon, required this.value});
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        Icon(icon, size: 14, color: AppColors.textHint),
+        const SizedBox(width: 4),
+        Text(
+          value,
+          style: const TextStyle(
+            fontSize: 13,
+            color: AppColors.textSecondary,
+          ),
+        ),
+      ],
+    );
+  }
+}

lib/screens/garage_screen.dart

@@ -7,9 +7,18 @@ import '../services/storage_service.dart';
 import '../theme/app_colors.dart';
 import '../widgets/car_card.dart';
 
-/// The "My Garage" screen — shows the user's collected cars in a grid.
+/// The "My Garage" screen — shows a collection's cars in a grid.
 class GarageScreen extends StatefulWidget {
-  const GarageScreen({super.key});
+  final String collectionId;
+  final String collectionName;
+  final bool isOwner;
+
+  const GarageScreen({
+    super.key,
+    required this.collectionId,
+    required this.collectionName,
+    this.isOwner = true,
+  });
 
   @override
   State<GarageScreen> createState() => GarageScreenState();
@@ -44,13 +53,10 @@ class GarageScreenState extends State<GarageScreen> {
     });
 
     try {
-      final userId = supabase.auth.currentUser?.id;
-      if (userId == null) return;
-
       final data = await supabase
           .from('hotwheels')
           .select()
-          .eq('user_id', userId)
+          .eq('collection_id', widget.collectionId)
           .order('created_at', ascending: false);
 
       if (!mounted) return;
@@ -91,7 +97,7 @@ class GarageScreenState extends State<GarageScreen> {
               titlePadding:
                   const EdgeInsets.only(left: 20, bottom: 16),
               title: Text(
-                'My Garage',
+                widget.collectionName,
                 style: TextStyle(
                   fontFamily: 'Poppins',
                   fontWeight: FontWeight.w700,

lib/screens/home_shell.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import 'garage_screen.dart';
+import 'collections_screen.dart';
 import 'scan_tab.dart';
 import 'profile_screen.dart';
 
@@ -13,19 +13,19 @@ class HomeShell extends StatefulWidget {
 
 class _HomeShellState extends State<HomeShell> {
   int _currentIndex = 0;
-  final _garageKey = GlobalKey<GarageScreenState>();
+  final _collectionsKey = GlobalKey<CollectionsScreenState>();
 
   late final List<Widget> _pages = <Widget>[
-    GarageScreen(key: _garageKey),
+    CollectionsScreen(key: _collectionsKey),
     const ScanTab(),
     const ProfileScreen(),
   ];
 
   void _onTabSelected(int i) {
     setState(() => _currentIndex = i);
-    // Refresh garage whenever user switches to it.
+    // Refresh collections whenever user switches to it.
     if (i == 0) {
-      _garageKey.currentState?.refresh();
+      _collectionsKey.currentState?.refresh();
     }
   }
 
@@ -41,9 +41,9 @@ class _HomeShellState extends State<HomeShell> {
         onDestinationSelected: _onTabSelected,
         destinations: const [
           NavigationDestination(
-            icon: Icon(Icons.garage_outlined),
+            icon: Icon(Icons.collections_bookmark_outlined),
-            selectedIcon: Icon(Icons.garage),
+            selectedIcon: Icon(Icons.collections_bookmark),
-            label: 'Garage',
+            label: 'Collections',
           ),
           NavigationDestination(
             icon: Icon(Icons.qr_code_scanner_outlined),

lib/screens/manage_collection_screen.dart

@@ -0,0 +1,425 @@
+import 'package:flutter/material.dart';
+import '../main.dart';
+import '../services/collection_service.dart';
+import '../theme/app_colors.dart';
+
+/// Screen to manage a collection: rename, invite/remove members, delete.
+class ManageCollectionScreen extends StatefulWidget {
+  final Collection collection;
+
+  const ManageCollectionScreen({super.key, required this.collection});
+
+  @override
+  State<ManageCollectionScreen> createState() =>
+      _ManageCollectionScreenState();
+}
+
+class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
+  late Collection _collection;
+  List<CollectionMember> _members = [];
+  bool _isLoading = true;
+
+  @override
+  void initState() {
+    super.initState();
+    _collection = widget.collection;
+    _loadMembers();
+  }
+
+  Future<void> _loadMembers() async {
+    setState(() => _isLoading = true);
+    try {
+      final members =
+          await CollectionService.getMembers(_collection.id);
+      if (!mounted) return;
+      setState(() {
+        _members = members;
+        _isLoading = false;
+      });
+    } catch (e) {
+      if (!mounted) return;
+      setState(() => _isLoading = false);
+      showGlobalSnackBar('Failed to load members: $e', isError: true);
+    }
+  }
+
+  Future<void> _rename() async {
+    final ctrl = TextEditingController(text: _collection.name);
+    final descCtrl =
+        TextEditingController(text: _collection.description ?? '');
+
+    final result = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        title: const Text('Rename Collection'),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            TextField(
+              controller: ctrl,
+              autofocus: true,
+              decoration: const InputDecoration(labelText: 'Name'),
+            ),
+            const SizedBox(height: 12),
+            TextField(
+              controller: descCtrl,
+              decoration:
+                  const InputDecoration(labelText: 'Description (optional)'),
+            ),
+          ],
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () {
+              if (ctrl.text.trim().isEmpty) return;
+              Navigator.pop(context, true);
+            },
+            child: const Text('Save'),
+          ),
+        ],
+      ),
+    );
+
+    if (result != true) return;
+
+    try {
+      await CollectionService.update(
+        collectionId: _collection.id,
+        name: ctrl.text.trim(),
+        description: descCtrl.text.trim(),
+      );
+      setState(() {
+        _collection = Collection(
+          id: _collection.id,
+          name: ctrl.text.trim(),
+          description: descCtrl.text.trim(),
+          ownerId: _collection.ownerId,
+          createdAt: _collection.createdAt,
+          role: _collection.role,
+          itemCount: _collection.itemCount,
+          memberCount: _collection.memberCount,
+        );
+      });
+      showGlobalSnackBar('Collection renamed!');
+    } catch (e) {
+      showGlobalSnackBar('Failed: $e', isError: true);
+    }
+  }
+
+  Future<void> _inviteMember() async {
+    final emailCtrl = TextEditingController();
+
+    final result = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        icon: Container(
+          padding: const EdgeInsets.all(12),
+          decoration: const BoxDecoration(
+            gradient: AppColors.brandGradient,
+            shape: BoxShape.circle,
+          ),
+          child: const Icon(Icons.person_add, color: Colors.white, size: 28),
+        ),
+        title: const Text('Invite Member'),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            const Text(
+              'Enter the email address of the person you want to invite. '
+              'They must already have an account.',
+              style: TextStyle(
+                fontSize: 13,
+                color: AppColors.textSecondary,
+              ),
+            ),
+            const SizedBox(height: 16),
+            TextField(
+              controller: emailCtrl,
+              autofocus: true,
+              keyboardType: TextInputType.emailAddress,
+              decoration: const InputDecoration(
+                labelText: 'Email address',
+                hintText: 'user@example.com',
+                prefixIcon: Icon(Icons.email_outlined),
+              ),
+            ),
+          ],
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () {
+              if (emailCtrl.text.trim().isEmpty) return;
+              Navigator.pop(context, true);
+            },
+            child: const Text('Invite'),
+          ),
+        ],
+      ),
+    );
+
+    if (result != true) return;
+
+    try {
+      await CollectionService.inviteByEmail(
+        collectionId: _collection.id,
+        email: emailCtrl.text.trim(),
+      );
+      showGlobalSnackBar('Member invited!');
+      _loadMembers();
+    } catch (e) {
+      showGlobalSnackBar('$e', isError: true);
+    }
+  }
+
+  Future<void> _removeMember(CollectionMember member) async {
+    final confirmed = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        title: const Text('Remove Member?'),
+        content: Text(
+            'Remove ${member.email} from this collection?'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context, false),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () => Navigator.pop(context, true),
+            style: ElevatedButton.styleFrom(backgroundColor: AppColors.error),
+            child: const Text('Remove'),
+          ),
+        ],
+      ),
+    );
+
+    if (confirmed != true) return;
+
+    try {
+      await CollectionService.removeMember(
+        collectionId: _collection.id,
+        membershipId: member.id,
+      );
+      showGlobalSnackBar('Member removed.');
+      _loadMembers();
+    } catch (e) {
+      showGlobalSnackBar('Failed: $e', isError: true);
+    }
+  }
+
+  Future<void> _leaveCollection() async {
+    final confirmed = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        title: const Text('Leave Collection?'),
+        content: Text(
+            'You will lose access to "${_collection.name}". '
+            'This action cannot be undone.'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context, false),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () => Navigator.pop(context, true),
+            style: ElevatedButton.styleFrom(backgroundColor: AppColors.error),
+            child: const Text('Leave'),
+          ),
+        ],
+      ),
+    );
+
+    if (confirmed != true) return;
+
+    try {
+      await CollectionService.leave(_collection.id);
+      showGlobalSnackBar('Left "${_collection.name}".');
+      if (mounted) Navigator.pop(context);
+    } catch (e) {
+      showGlobalSnackBar('Failed: $e', isError: true);
+    }
+  }
+
+  Future<void> _deleteCollection() async {
+    final confirmed = await showDialog<bool>(
+      context: context,
+      builder: (_) => AlertDialog(
+        title: const Text('Delete Collection?'),
+        content: Text(
+            'Delete "${_collection.name}" and ALL its items? '
+            'This cannot be undone.'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context, false),
+            child: const Text('Cancel'),
+          ),
+          ElevatedButton(
+            onPressed: () => Navigator.pop(context, true),
+            style: ElevatedButton.styleFrom(backgroundColor: AppColors.error),
+            child: const Text('Delete Forever'),
+          ),
+        ],
+      ),
+    );
+
+    if (confirmed != true) return;
+
+    try {
+      await CollectionService.delete(_collection.id);
+      showGlobalSnackBar('Collection deleted.');
+      if (mounted) Navigator.pop(context);
+    } catch (e) {
+      showGlobalSnackBar('Failed: $e', isError: true);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final currentUserId = supabase.auth.currentUser?.id;
+
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(_collection.name),
+        actions: [
+          if (_collection.isOwner)
+            IconButton(
+              icon: const Icon(Icons.edit),
+              tooltip: 'Rename',
+              onPressed: _rename,
+            ),
+        ],
+      ),
+      body: ListView(
+        padding: const EdgeInsets.all(16),
+        children: [
+          // ── Description ──
+          if (_collection.description != null &&
+              _collection.description!.isNotEmpty) ...[
+            Text(
+              _collection.description!,
+              style: const TextStyle(
+                  fontSize: 14, color: AppColors.textSecondary),
+            ),
+            const SizedBox(height: 16),
+          ],
+
+          // ── Members section ──
+          Row(
+            children: [
+              Text(
+                'Members',
+                style: theme.textTheme.titleMedium?.copyWith(
+                  fontWeight: FontWeight.w600,
+                ),
+              ),
+              const Spacer(),
+              if (_collection.isOwner)
+                TextButton.icon(
+                  onPressed: _inviteMember,
+                  icon: const Icon(Icons.person_add, size: 18),
+                  label: const Text('Invite'),
+                ),
+            ],
+          ),
+          const SizedBox(height: 8),
+
+          if (_isLoading)
+            const Center(
+              child: Padding(
+                padding: EdgeInsets.all(24),
+                child: CircularProgressIndicator(),
+              ),
+            )
+          else
+            ...List.generate(_members.length, (i) {
+              final m = _members[i];
+              return Card(
+                margin: const EdgeInsets.only(bottom: 8),
+                child: ListTile(
+                  leading: CircleAvatar(
+                    backgroundColor: m.isOwner
+                        ? AppColors.orange
+                        : AppColors.navy,
+                    child: Icon(
+                      m.isOwner ? Icons.star : Icons.person,
+                      color: Colors.white,
+                      size: 20,
+                    ),
+                  ),
+                  title: Text(
+                    m.email,
+                    style: const TextStyle(fontWeight: FontWeight.w500),
+                  ),
+                  subtitle: Text(
+                    m.isOwner ? 'Owner' : 'Member',
+                    style: const TextStyle(fontSize: 12),
+                  ),
+                  trailing: (!m.isOwner &&
+                          _collection.isOwner &&
+                          m.userId != currentUserId)
+                      ? IconButton(
+                          icon: const Icon(Icons.remove_circle_outline,
+                              color: AppColors.error),
+                          onPressed: () => _removeMember(m),
+                        )
+                      : null,
+                ),
+              );
+            }),
+
+          const SizedBox(height: 32),
+          const Divider(),
+          const SizedBox(height: 16),
+
+          // ── Danger zone ──
+          Text(
+            'Danger Zone',
+            style: theme.textTheme.titleMedium?.copyWith(
+              fontWeight: FontWeight.w600,
+              color: AppColors.error,
+            ),
+          ),
+          const SizedBox(height: 12),
+
+          if (!_collection.isOwner)
+            SizedBox(
+              width: double.infinity,
+              child: OutlinedButton.icon(
+                onPressed: _leaveCollection,
+                icon: const Icon(Icons.exit_to_app, color: AppColors.error),
+                label: const Text('Leave Collection',
+                    style: TextStyle(color: AppColors.error)),
+                style: OutlinedButton.styleFrom(
+                  side: const BorderSide(color: AppColors.error),
+                  padding: const EdgeInsets.symmetric(vertical: 14),
+                ),
+              ),
+            ),
+
+          if (_collection.isOwner)
+            SizedBox(
+              width: double.infinity,
+              child: OutlinedButton.icon(
+                onPressed: _deleteCollection,
+                icon: const Icon(Icons.delete_forever, color: AppColors.error),
+                label: const Text('Delete Collection',
+                    style: TextStyle(color: AppColors.error)),
+                style: OutlinedButton.styleFrom(
+                  side: const BorderSide(color: AppColors.error),
+                  padding: const EdgeInsets.symmetric(vertical: 14),
+                ),
+              ),
+            ),
+        ],
+      ),
+    );
+  }
+}

lib/screens/scan_tab.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 import 'package:image_picker/image_picker.dart';
 import '../main.dart';
 import '../scanner_screen.dart';
+import '../services/collection_service.dart';
 import '../services/storage_service.dart';
 import '../theme/app_colors.dart';
 
@@ -17,6 +18,30 @@ class ScanTab extends StatefulWidget {
 
 class _ScanTabState extends State<ScanTab> {
   bool _isBusy = false;
+  List<Collection> _collections = [];
+  Collection? _selectedCollection;
+  bool _loadingCollections = true;
+
+  @override
+  void initState() {
+    super.initState();
+    _loadCollections();
+  }
+
+  Future<void> _loadCollections() async {
+    try {
+      final list = await CollectionService.getMyCollections();
+      if (!mounted) return;
+      setState(() {
+        _collections = list;
+        _selectedCollection = list.isNotEmpty ? list.first : null;
+        _loadingCollections = false;
+      });
+    } catch (e) {
+      if (!mounted) return;
+      setState(() => _loadingCollections = false);
+    }
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -51,7 +76,7 @@ class _ScanTabState extends State<ScanTab> {
               ),
               const SizedBox(height: 10),
               const Text(
-                'Point your camera at the model ID on the\npackaging to instantly add it to your garage.',
+                'Point your camera at the model ID on the\npackaging to instantly add it to your collection.',
                 textAlign: TextAlign.center,
                 style: TextStyle(
                   fontSize: 14,
@@ -59,7 +84,72 @@ class _ScanTabState extends State<ScanTab> {
                   height: 1.5,
                 ),
               ),
-              const SizedBox(height: 36),
+              const SizedBox(height: 24),
+
+              // ── Collection picker ──
+              if (_loadingCollections)
+                const Padding(
+                  padding: EdgeInsets.symmetric(vertical: 8),
+                  child: SizedBox(
+                    width: 20,
+                    height: 20,
+                    child: CircularProgressIndicator(strokeWidth: 2),
+                  ),
+                )
+              else if (_collections.isEmpty)
+                const Text(
+                  'Create a collection first!',
+                  style: TextStyle(color: AppColors.error),
+                )
+              else
+                Container(
+                  width: double.infinity,
+                  padding: const EdgeInsets.symmetric(horizontal: 16),
+                  decoration: BoxDecoration(
+                    borderRadius: BorderRadius.circular(14),
+                    border: Border.all(
+                      color: AppColors.orange.withValues(alpha: 0.4),
+                    ),
+                  ),
+                  child: DropdownButtonHideUnderline(
+                    child: DropdownButton<String>(
+                      isExpanded: true,
+                      value: _selectedCollection?.id,
+                      icon: const Icon(Icons.arrow_drop_down,
+                          color: AppColors.orange),
+                      items: _collections
+                          .map((c) => DropdownMenuItem(
+                                value: c.id,
+                                child: Row(
+                                  children: [
+                                    Icon(
+                                      c.isOwner
+                                          ? Icons.collections_bookmark
+                                          : Icons.group,
+                                      size: 18,
+                                      color: AppColors.orange,
+                                    ),
+                                    const SizedBox(width: 8),
+                                    Expanded(
+                                      child: Text(
+                                        c.name,
+                                        overflow: TextOverflow.ellipsis,
+                                      ),
+                                    ),
+                                  ],
+                                ),
+                              ))
+                          .toList(),
+                      onChanged: (id) {
+                        setState(() {
+                          _selectedCollection = _collections
+                              .firstWhere((c) => c.id == id);
+                        });
+                      },
+                    ),
+                  ),
+                ),
+              const SizedBox(height: 24),
 
               // ── Scan button (gradient) ──
               SizedBox(
@@ -78,7 +168,9 @@ class _ScanTabState extends State<ScanTab> {
                     ],
                   ),
                   child: ElevatedButton.icon(
-                    onPressed: _isBusy ? null : _openScanner,
+                    onPressed: _isBusy || _selectedCollection == null
+                        ? null
+                        : _openScanner,
                     icon: _isBusy
                         ? const SizedBox(
                             width: 22,
@@ -113,7 +205,9 @@ class _ScanTabState extends State<ScanTab> {
               SizedBox(
                 width: double.infinity,
                 child: OutlinedButton.icon(
-                  onPressed: _isBusy ? null : _manualEntry,
+                  onPressed: _isBusy || _selectedCollection == null
+                      ? null
+                      : _manualEntry,
                   icon: const Icon(Icons.keyboard),
                   label: const Text('Enter ID Manually'),
                 ),
@@ -171,13 +265,18 @@ class _ScanTabState extends State<ScanTab> {
   }
 
   Future<void> _processHwId(String hwId) async {
+    final collection = _selectedCollection;
+    if (collection == null) return;
+
     setState(() => _isBusy = true);
 
     try {
+      // Check if this hw_id already exists in the selected collection.
       final data = await supabase
           .from('hotwheels')
           .select()
           .eq('hw_id', hwId)
+          .eq('collection_id', collection.id)
           .maybeSingle();
 
       if (!mounted) return;
@@ -190,9 +289,9 @@ class _ScanTabState extends State<ScanTab> {
           builder: (_) => AlertDialog(
             icon: const Icon(Icons.check_circle,
                 color: AppColors.success, size: 48),
-            title: const Text('Already in Garage!'),
+            title: const Text('Already in Collection!'),
             content:
-                Text('$hwId is already in your collection.'),
+                Text('$hwId is already in "${collection.name}".'),
             actions: [
               ElevatedButton(
                 onPressed: () => Navigator.pop(context),
@@ -205,10 +304,14 @@ class _ScanTabState extends State<ScanTab> {
         // New — offer to add
         final added = await showDialog<bool>(
           context: context,
-          builder: (_) => _AddCarDialog(hwId: hwId),
+          builder: (_) => _AddCarDialog(
+            hwId: hwId,
+            collectionId: collection.id,
+            collectionName: collection.name,
+          ),
         );
         if (added == true) {
-          showGlobalSnackBar('$hwId added to your garage! 🎉');
+          showGlobalSnackBar('$hwId added to "${collection.name}"! 🎉');
         }
       }
     } catch (e) {
@@ -221,7 +324,13 @@ class _ScanTabState extends State<ScanTab> {
 // ── Add Car Dialog (inline, styled) ──────────────────────────────────
 class _AddCarDialog extends StatefulWidget {
   final String hwId;
-  const _AddCarDialog({required this.hwId});
+  final String collectionId;
+  final String collectionName;
+  const _AddCarDialog({
+    required this.hwId,
+    required this.collectionId,
+    required this.collectionName,
+  });
 
   @override
   State<_AddCarDialog> createState() => _AddCarDialogState();
@@ -263,6 +372,7 @@ class _AddCarDialogState extends State<_AddCarDialog> {
       await supabase.from('hotwheels').insert({
         'hw_id': widget.hwId,
         'user_id': supabase.auth.currentUser!.id,
+        'collection_id': widget.collectionId,
       });
       if (!mounted) return;
       Navigator.pop(context, true);
@@ -280,6 +390,7 @@ class _AddCarDialogState extends State<_AddCarDialog> {
       final row = <String, dynamic>{
         'hw_id': widget.hwId,
         'user_id': supabase.auth.currentUser!.id,
+        'collection_id': widget.collectionId,
       };
 
       // Optional fields — only include if filled in.
@@ -441,7 +552,7 @@ class _AddCarDialogState extends State<_AddCarDialog> {
                   height: 18,
                   child: CircularProgressIndicator(strokeWidth: 2),
                 )
-              : const Text('Add to Garage'),
+              : const Text('Add to Collection'),
         ),
       ],
     );

lib/services/collection_service.dart

@@ -0,0 +1,236 @@
+import 'package:supabase_flutter/supabase_flutter.dart';
+import '../main.dart';
+
+/// Data model for a collection.
+class Collection {
+  final String id;
+  final String name;
+  final String? description;
+  final String ownerId;
+  final DateTime createdAt;
+  final String role; // 'owner' or 'member'
+  final int itemCount;
+  final int memberCount;
+
+  Collection({
+    required this.id,
+    required this.name,
+    this.description,
+    required this.ownerId,
+    required this.createdAt,
+    required this.role,
+    this.itemCount = 0,
+    this.memberCount = 1,
+  });
+
+  bool get isOwner => role == 'owner';
+}
+
+/// Member of a collection.
+class CollectionMember {
+  final String id;
+  final String userId;
+  final String email;
+  final String role;
+  final DateTime joinedAt;
+
+  CollectionMember({
+    required this.id,
+    required this.userId,
+    required this.email,
+    required this.role,
+    required this.joinedAt,
+  });
+
+  bool get isOwner => role == 'owner';
+}
+
+/// Service for managing collections and membership.
+class CollectionService {
+  CollectionService._();
+
+  /// Fetch all collections the current user is a member of,
+  /// including item count and member count.
+  static Future<List<Collection>> getMyCollections() async {
+    final userId = supabase.auth.currentUser!.id;
+
+    // Get memberships with collection data.
+    final memberships = await supabase
+        .from('collection_members')
+        .select('role, collections(id, name, description, owner_id, created_at)')
+        .eq('user_id', userId);
+
+    final collections = <Collection>[];
+
+    for (final m in memberships) {
+      final c = m['collections'] as Map<String, dynamic>;
+
+      // Count items in this collection.
+      final itemCount = await supabase
+          .from('hotwheels')
+          .select('id')
+          .eq('collection_id', c['id'])
+          .count(CountOption.exact);
+
+      // Count members.
+      final memberCount = await supabase
+          .from('collection_members')
+          .select('id')
+          .eq('collection_id', c['id'])
+          .count(CountOption.exact);
+
+      collections.add(Collection(
+        id: c['id'] as String,
+        name: c['name'] as String,
+        description: c['description'] as String?,
+        ownerId: c['owner_id'] as String,
+        createdAt: DateTime.parse(c['created_at'] as String),
+        role: m['role'] as String,
+        itemCount: itemCount.count,
+        memberCount: memberCount.count,
+      ));
+    }
+
+    // Sort: owned first, then by name.
+    collections.sort((a, b) {
+      if (a.isOwner && !b.isOwner) return -1;
+      if (!a.isOwner && b.isOwner) return 1;
+      return a.name.compareTo(b.name);
+    });
+
+    return collections;
+  }
+
+  /// Create a new collection. The caller is automatically added as owner.
+  static Future<Collection> create({
+    required String name,
+    String? description,
+  }) async {
+    final userId = supabase.auth.currentUser!.id;
+
+    final row = await supabase
+        .from('collections')
+        .insert({
+          'name': name,
+          'owner_id': userId,
+          if (description != null && description.isNotEmpty)
+            'description': description,
+        })
+        .select()
+        .single();
+
+    // Add owner as a member.
+    await supabase.from('collection_members').insert({
+      'collection_id': row['id'],
+      'user_id': userId,
+      'role': 'owner',
+    });
+
+    return Collection(
+      id: row['id'] as String,
+      name: row['name'] as String,
+      description: row['description'] as String?,
+      ownerId: userId,
+      createdAt: DateTime.parse(row['created_at'] as String),
+      role: 'owner',
+      itemCount: 0,
+      memberCount: 1,
+    );
+  }
+
+  /// Update a collection's name/description. Owner only.
+  static Future<void> update({
+    required String collectionId,
+    required String name,
+    String? description,
+  }) async {
+    await supabase.from('collections').update({
+      'name': name,
+      'description': description,
+    }).eq('id', collectionId);
+  }
+
+  /// Delete a collection. Owner only. Cascade deletes members & items.
+  static Future<void> delete(String collectionId) async {
+    await supabase.from('collections').delete().eq('id', collectionId);
+  }
+
+  /// Get members of a collection (with emails via RPC).
+  static Future<List<CollectionMember>> getMembers(
+      String collectionId) async {
+    final rows = await supabase.rpc('get_collection_members', params: {
+      'p_collection_id': collectionId,
+    });
+
+    final members = <CollectionMember>[];
+    for (final r in rows) {
+      members.add(CollectionMember(
+        id: r['id'] as String,
+        userId: r['user_id'] as String,
+        email: r['email'] as String? ?? 'unknown',
+        role: r['role'] as String,
+        joinedAt: DateTime.parse(r['created_at'] as String),
+      ));
+    }
+
+    return members;
+  }
+
+  /// Invite a user by email. Looks up auth.users via an RPC function,
+  /// then inserts a collection_members row.
+  static Future<void> inviteByEmail({
+    required String collectionId,
+    required String email,
+  }) async {
+    // Call an RPC to look up the user ID by email.
+    final result = await supabase.rpc('get_user_id_by_email', params: {
+      'lookup_email': email.trim().toLowerCase(),
+    });
+
+    if (result == null || (result is List && result.isEmpty)) {
+      throw Exception(
+          'No user found with that email. They must create an account first.');
+    }
+
+    final userId = result is List ? result.first['id'] as String : result as String;
+
+    // Check if already a member.
+    final existing = await supabase
+        .from('collection_members')
+        .select('id')
+        .eq('collection_id', collectionId)
+        .eq('user_id', userId)
+        .maybeSingle();
+
+    if (existing != null) {
+      throw Exception('This user is already a member of this collection.');
+    }
+
+    await supabase.from('collection_members').insert({
+      'collection_id': collectionId,
+      'user_id': userId,
+      'role': 'member',
+    });
+  }
+
+  /// Remove a member from a collection.
+  static Future<void> removeMember({
+    required String collectionId,
+    required String membershipId,
+  }) async {
+    await supabase
+        .from('collection_members')
+        .delete()
+        .eq('id', membershipId);
+  }
+
+  /// Leave a collection (for non-owners).
+  static Future<void> leave(String collectionId) async {
+    final userId = supabase.auth.currentUser!.id;
+    await supabase
+        .from('collection_members')
+        .delete()
+        .eq('collection_id', collectionId)
+        .eq('user_id', userId);
+  }
+}