[mob][photos] Get four random prompt data from json

mobile/lib/services/magic_cache_service.dart

@@ -0,0 +1,66 @@
+import 'dart:math';
+
+import "package:logging/logging.dart";
+import "package:shared_preferences/shared_preferences.dart";
+
+const _promptsJson = {
+  "prompts": [
+    {
+      "prompt": "identity document",
+      "title": "Identity Document",
+      "minimumScore": 0.269,
+      "minimumSize": 0.0,
+    },
+    {
+      "prompt": "sunset at the beach",
+      "title": "Sunset",
+      "minimumScore": 0.25,
+      "minimumSize": 0.0,
+    },
+    {
+      "prompt": "roadtrip",
+      "title": "Roadtrip",
+      "minimumScore": 0.26,
+      "minimumSize": 0.0,
+    },
+    {
+      "prompt": "pizza pasta burger",
+      "title": "Food",
+      "minimumScore": 0.27,
+      "minimumSize": 0.0,
+    }
+  ],
+};
+
+class MagicCacheService {
+  static const _key = "magic";
+  late SharedPreferences prefs;
+  final Logger _logger = Logger((MagicCacheService).toString());
+  MagicCacheService._privateConstructor();
+
+  static final MagicCacheService instance =
+      MagicCacheService._privateConstructor();
+
+  void init(SharedPreferences preferences) {
+    prefs = preferences;
+  }
+
+  List<Map<String, Object>> getRandomPrompts() {
+    final promptsJson = _promptsJson["prompts"];
+    final randomPrompts = <Map<String, Object>>[];
+    final randomNumbers = _generateRandomNumbers(promptsJson!.length - 1, 4);
+    for (int i = 0; i < randomNumbers.length; i++) {
+      randomPrompts.add(promptsJson[randomNumbers[i]]);
+    }
+
+    return randomPrompts;
+  }
+
+  List<int> _generateRandomNumbers(int max, int count) {
+    final numbers = <int>[];
+    for (int i = 1; i <= count; i++) {
+      numbers.add(Random().nextInt(max + 1));
+    }
+    return numbers;
+  }
+}