CircularBufferEnqueue.swift

class CircularBuffer<T> {

  // ...
  
  func enqueue(item: T) {
    
    // 1.
    if isEmpty() {
      elements[bufferMaxSize-1] = item
    } else {  
    
      // 2.
      for index in 0...bufferMaxSize - 2 {
        elements[index] = elements[index + 1]
      }
      
      // 3.
      elements[bufferMaxSize - 1] = item
    }

    // 4.
    if !isFull() {
      size += 1
    }
  }
}