module Exam
  # create a DList
  class DList

    include Enumerable

    attr_accessor :head, :tail

    def each
    	aux=@head
    	while aux[:next]
    		yield aux[:value]
    		aux=aux[:next]
    	end
    	yield aux[:value]
    end


    def initialize(v)
      if v.kind_of?(Array)
        @head = Node.new(v[0],nil, nil)
        v.shift
        pushHead(v)
      else
        @head = Node.new(v, nil, nil)
      end
    end

    def popHead
      nodo = @head
      if nodo
      	@head=@head[:next]
      	if @head
      		@head[:prev]=nil
      	end
        	return nodo[:value]
      end
    end

    def popTail
    	nodo = @head
    	if nodo
    		while nodo[:next] do
        		nodo=nodo[:next]
      	end
      	aux=nodo[:prev]
      	aux[:next]=nil
      	nodo[:prev]=nil
      	return nodo[:value]
      end
    end

    def pushHead(v)
      if v.kind_of?(Array)
        for i in 0..v.size-1
            aux = @head
            nodo=Node.new(v[i], aux, nil)
            @head=nodo
            aux[:prev]=@head
        end
      else
        aux = @head
        nodo=Node.new(v, aux, nil)
        @head=nodo
        aux[:prev]=@head
      end
    end

      def pushTail(v)
  	    aux = @head

  	    if v.kind_of?(Array)
  	      for i in 0..v.size-1
  	        while aux[:next]!=nil do
  	          aux=aux[:next]
  	        end
  	        nuevo_nodo=Node.new(v[i], nil, aux)
  	        aux[:next]=nuevo_nodo
  	      end
  	    else
  	      while aux[:next] do
  	        aux=aux[:next]
  	      end
  	      nuevo_nodo=Node.new(v, nil, aux)
  	      aux[:next]=nuevo_nodo
  	    end
    end

    def size
      aux=@head
      n=0
      while aux[:next] do
        n=n+1
        aux=aux[:next]
      end
      n=n+1
    end

    def to_s
      aux=@head
      s=""
      while aux[:next] do
        s = s + "#{aux[:value]} "
        aux=aux[:next]
      end
      s = s + "#{aux[:value]}"
      #puts "#{s}"
    end

    def to_is
      aux=@head
      s=""
      while aux[:next] do
        aux=aux[:next]
      end
      while aux[:prev] do
        s = s + "#{aux[:value]} "
        aux=aux[:prev]
      end
      s = s + "#{aux[:value]}"
      #puts "#{s}"
    end
  end
end