CircularBufferFull.swift

class CircularBuffer<T> {
    
  var bufferMaxSize: Int
  var size = 0
  var elements = Array<T?>(repeating: nil, count: 8)

  var front: T? {
    if isEmpty() {
      return nil
    } else {
      return elements[bufferMaxSize - size]
    }
  }

  init(maxSize: Int) {
    self.bufferMaxSize = maxSize
    self.elements = Array(repeating: nil, count: self.bufferMaxSize)
  }

  convenience init() {
    self.init(maxSize: 8)
  }

  func isEmpty() -> Bool {
    return self.size == 0
  }

  func isFull() -> Bool {
    return size == bufferMaxSize
  }

  func enqueue(item: T) {
    // if empty, update last element to be the item
    if isEmpty() {
      elements[bufferMaxSize-1] = item
    } else {
      // if not empty, loop through the indexes and update the item to be that of the one ahead
      for index in 0...bufferMaxSize - 2 {
        elements[index] = elements[index + 1]
      }
      // after shifting all elements, update the last item to be the item enqueued
      elements[bufferMaxSize - 1] = item
    }
    // increase the size only if the buffer isnt full
    if !isFull() {
      size += 1
    }
  }

  func dequeue() -> T? {
    
    if !isEmpty() {
      // set a variable to equal the front item, update it to nil, and return the front item 
      let front = elements[bufferMaxSize - size]
      elements[bufferMaxSize - size] = nil
      size -= 1
      return front
    }
    // return nil buffer is empty
    return nil
  }
}

let circularBuffer = CircularBuffer<Int>(maxSize: 4)

circularBuffer.elements     // [nil, nil, nil, nil]
circularBuffer.front        // nil
circularBuffer.size         // 0
circularBuffer.bufferMaxSize // 4
circularBuffer.isFull()     // false
circularBuffer.isEmpty()    // true

circularBuffer.enqueue(item: 7)
circularBuffer.elements // [nil, nil, nil, 7]
circularBuffer.front    // 7
circularBuffer.size     // 1
circularBuffer.isEmpty()// false

circularBuffer.enqueue(item: 8)
circularBuffer.elements // [nil, nil, 7, 8]
circularBuffer.front    // 7
circularBuffer.size     // 2

circularBuffer.enqueue(item: 9)
circularBuffer.elements // [nil, 7, 8, 9]

circularBuffer.enqueue(item: 10)
circularBuffer.elements // [7, 8, 9, 10]

circularBuffer.enqueue(item: 11)
circularBuffer.elements // [8, 9, 10, 11]

circularBuffer.dequeue() // 8
circularBuffer.elements  // [nil, 9, 10, 11]