Feat: Implement shopping list importing

lib/screens/home_screen.dart

@@ -4,6 +4,7 @@ import 'package:shopping_list_but_free/models/shopping_list.dart';
 import 'package:shopping_list_but_free/objectbox.dart';
 import 'package:shopping_list_but_free/screens/shopping_list_screen.dart';
 import 'package:shopping_list_but_free/widgets/add_shopping_list.dart';
+import 'package:shopping_list_but_free/widgets/import_shopping_list.dart';
 import 'package:shopping_list_but_free/widgets/main_navigation_drawer.dart';
 
 /// A widget that displays the home screen
@@ -21,6 +22,19 @@ class HomeScreen extends StatelessWidget {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Shopping List But Free'),
+        actions: [
+          IconButton(
+            tooltip: 'Import',
+            onPressed: () {
+              Navigator.of(context).push(
+                PageRouteBuilder(
+                    opaque: false,
+                    pageBuilder: (_, __, ___) => const ImportShoppingList()),
+              );
+            },
+            icon: const Icon(Icons.download_outlined),
+          )
+        ],
       ),
       drawer: const MainNavigationDrawer(),
       floatingActionButton: FloatingActionButton(

lib/widgets/import_shopping_list.dart

@@ -0,0 +1,122 @@
+import 'dart:convert';
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import 'package:shopping_list_but_free/models/collection.dart';
+import 'package:shopping_list_but_free/models/shopping_item.dart';
+import 'package:shopping_list_but_free/models/shopping_list.dart';
+import 'package:shopping_list_but_free/objectbox.dart';
+import 'package:shopping_list_but_free/objectbox.g.dart';
+import 'package:shopping_list_but_free/screens/shopping_list_screen.dart';
+
+/// Displays a card that lets the user copy the Json encoding of
+/// [shoppingList]
+class ImportShoppingList extends StatefulWidget {
+  const ImportShoppingList({
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  State<ImportShoppingList> createState() => _ImportShoppingListState();
+}
+
+/// Import a ShoppingList by creating a new ShoppingList from given
+/// shopping list json.
+class _ImportShoppingListState extends State<ImportShoppingList> {
+  String shoppingListJson = '';
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      backgroundColor: Colors.black.withOpacity(0.5),
+      body: Stack(
+        children: [
+          GestureDetector(
+            onTap: () {
+              Navigator.of(context).pop();
+            },
+          ),
+          Center(
+            child: SizedBox(
+              width: min(MediaQuery.of(context).size.width - 10, 300),
+              height: MediaQuery.of(context).size.height / 3,
+              child: Card(
+                elevation: 20,
+                child: Column(
+                  mainAxisAlignment: MainAxisAlignment.spaceAround,
+                  children: [
+                    Expanded(
+                      flex: 0,
+                      child: Padding(
+                        padding: const EdgeInsets.all(20.0),
+                        child: TextField(
+                          autocorrect: false,
+                          decoration: const InputDecoration(
+                            hintText: 'Enter shopping list code',
+                          ),
+                          onChanged: (String value) {
+                            setState(() {
+                              shoppingListJson = value.trim();
+                            });
+                          },
+                          onSubmitted: (value) {
+                            _import();
+                          },
+                        ),
+                      ),
+                    ),
+                    IconButton(
+                      tooltip: 'Import',
+                      onPressed: () {
+                        _import();
+                      },
+                      icon: const Icon(Icons.download_outlined),
+                    ),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+
+  void _import() {
+    final shoppingListMap = json.decode(shoppingListJson);
+
+    final shoppingList = ShoppingList(name: shoppingListMap['name']);
+
+    for (var shoppingItemMap in shoppingListMap['shoppingItems']) {
+      // Create ShoppingItem
+      final shoppingItem = ShoppingItem(name: shoppingItemMap['name']);
+      shoppingItem.checked = shoppingItemMap['checked'];
+      shoppingItem.quantity = shoppingItemMap['quantity'];
+
+      // Add shoppingItem to the others Collection if is not in any other Collection
+      if (!objectbox.collectionBox.getAll().any((collection) => collection
+          .shoppingItemsNames
+          .contains(shoppingItem.name.toLowerCase()))) {
+        final others = objectbox.collectionBox
+            .query(Collection_.name.equals('Others'))
+            .build()
+            .findFirst() as Collection;
+
+        others.shoppingItemsNames.add(shoppingItem.name.toLowerCase());
+
+        objectbox.collectionBox.put(others);
+      }
+
+      shoppingList.shoppingItems.add(shoppingItem);
+    }
+
+    objectbox.shoppingListBox.put(shoppingList);
+
+    Navigator.of(context).pushReplacement(
+      MaterialPageRoute(
+        builder: (context) =>
+            ShoppingListScreen(shoppingListId: shoppingList.id),
+      ),
+    );
+  }
+}