# Roughly following https://learnersbucket.com/tutorials/data-structures/implement-deque-data-structure-in-javascript/

export default class Deque
   constructor: -> 
      @clear()
  
   insertLeft: (elm) ->   # Add an item on the left
      if @left_full > 0
         @items[--@left_full] = elm
      else
         @right_open++
         @items.unshift elm

   insertRight: (elm) ->  # Add an item on the right of the list
      @items[@right_open++] = elm

   removeLeft: ->         # Remove the item from the left
      @nonempty() and @items[@left_full++]

   removeRight: ->        # Remove the item from the right
      @nonempty() and @items[--@right_open]

   left: ->               # Peek the leftmost element
      @nonempty and @items[@left_full]

   right: ->              # Peek the last element
      @nonempty and @items[@right_open - 1]

   nonempty: ->           # Returns null if no elements
      (@right_open > @left_full) or null

   empty: ->              # Returns null if any elements
      (@right_open is @left_full) or null

   size: ->               # Number of elements
      @right_open - @left_full

   clear: ->              # Remove all elements
      @right_open = @left_full = 0
      @items = []

   toString: ->
      "<#{@items[@left...@right].join(",")}>"