feat(user-sessions): introduce GameLobby and GameUtil for session management and code generation

knockoutwhistweb/app/util/GameUtil.scala

@@ -0,0 +1,29 @@
+package util
+
+import scala.util.Random
+
+object GameUtil {
+
+  private val CharPool: String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
+  private val CodeLength: Int = 6
+  private val MaxRepetition: Int = 2
+  private val random = new Random()
+
+  def generateCode(): String = {
+    val freq = Array.fill(CharPool.length)(0)
+    val code = new StringBuilder(CodeLength)
+
+    for (_ <- 0 until CodeLength) {
+      var index = random.nextInt(CharPool.length)
+      // Pick a new character if it's already used twice
+      while (freq(index) >= MaxRepetition) {
+        index = random.nextInt(CharPool.length)
+      }
+      freq(index) += 1
+      code.append(CharPool.charAt(index))
+    }
+
+    code.toString()
+  }
+  
+}