1 files changed, 44 insertions, 0 deletions
diff --git a/Firestore/Source/Util/FSTUtil.m b/Firestore/Source/Util/FSTUtil.m
new file mode 100644
index 0000000..d14c429
--- /dev/null
+++ b/Firestore/Source/Util/FSTUtil.m
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2017 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import "FSTUtil.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+static const double kArc4RandomMax = 0x100000000;
+
+static const int kAutoIDLength = 20;
+static NSString *const kAutoIDAlphabet =
+    @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+
+@implementation FSTUtil
+
++ (double)randomDouble {
+  return ((double)arc4random() / kArc4RandomMax);
+}
+
++ (NSString *)autoID {
+  unichar autoID[kAutoIDLength];
+  for (int i = 0; i < kAutoIDLength; i++) {
+    uint32_t randIndex = arc4random_uniform((uint32_t)kAutoIDAlphabet.length);
+    autoID[i] = [kAutoIDAlphabet characterAtIndex:randIndex];
+  }
+  return [NSString stringWithCharacters:autoID length:kAutoIDLength];
+}
+
+@end
+
+NS_ASSUME_NONNULL_END