first commit

lib/game/engine.dart

@@ -0,0 +1,66 @@
+import 'dart:math';
+
+import 'types.dart';
+
+final Random _random = Random();
+
+List<T> shuffleList<T>(List<T> arr) {
+  final a = List<T>.from(arr);
+  for (int i = a.length - 1; i > 0; i--) {
+    final int j = _random.nextInt(i + 1);
+    final T temp = a[i];
+    a[i] = a[j];
+    a[j] = temp;
+  }
+  return a;
+}
+
+List<CardModel> createDeck({
+  required int rows,
+  required int totalCards,
+  required int poolSize,
+  required List<String> allFaceIds,
+}) {
+  if (totalCards <= 0) {
+    throw Exception('totalCards must be > 0');
+  }
+  if (totalCards.isOdd) {
+    throw Exception('totalCards must be even');
+  }
+  if (allFaceIds.isEmpty) {
+    throw Exception('allFaceIds must not be empty');
+  }
+
+  final pairs = totalCards ~/ 2;
+  final actualPoolSize = poolSize.clamp(1, allFaceIds.length);
+  final pool = shuffleList(allFaceIds).take(actualPoolSize).toList();
+
+  if (pool.isEmpty) {
+    throw Exception('pool must not be empty');
+  }
+
+  final List<String> picked = [];
+  if (pool.length >= pairs) {
+    picked.addAll(shuffleList(pool).take(pairs));
+  } else {
+    picked.addAll(pool);
+    final remain = pairs - pool.length;
+    for (int i = 0; i < remain; i++) {
+      picked.add(pool[_random.nextInt(pool.length)]);
+    }
+  }
+
+  final doubled = picked.expand((e) => [e, e]).toList();
+  final shuffled = shuffleList(doubled);
+
+  return shuffled.asMap().entries.map((entry) {
+    final idx = entry.key;
+    final faceId = entry.value;
+    return CardModel(
+      id: '$faceId-$idx-${_random.nextInt(1 << 32).toRadixString(16)}',
+      faceId: faceId,
+      isFlipped: false,
+      isMatched: false,
+    );
+  }).toList();
+}