module(... or "Queue",package.seeall)

--Initializes a new queue
--@return Index table
function new ()
  return {head = 0, tail = -1}
end

--Adds element to the queue
--Inserts are FIFO
--@param queue Queue
--@param value Value of new element
function add (queue, value)
  local last = queue.tail + 1
  queue.tail = last
  queue[last] = value
end

--Removes element from queue
--Deletions are FIFO
--@param queue Queue
--@return True if operation was succesfull
--@return Error string
function remove (queue)
  local first = queue.head
  if first > queue.tail then
    return false, "Queue is empty"
  end
  local value = queue[first]
  queue[first] = nil
  queue.head = first + 1
  return true, value
end

--Returns true if queue is empty
--@param queue Queue
--@return True if given queue is empty
function is_empty(queue)
  if queue.head > queue.tail then
    return true
  end
  return false
end