;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>		 
;;;  		       								 
;;;  This program is free software; you can redistribute it and/or modify	 
;;;  it under the terms of the GNU General Public License as published by	 
;;;  the Free Software Foundation; either version 2 of the License, or		 
;;;  (at your option) any later version.					 
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;;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the		 
;;;  GNU General Public License for more details.				 
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;;;  You should have received a copy of the GNU General Public License		 
;;;  along with this program; if not, write to the Free Software 		 
;;;  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.	 
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(defpackage "PRIORITY-QUEUE"
  (:use :cl :heap)
  (:export "PRIORITY-QUEUE"
	   "PRIORITY-QUEUE-ELEMENT-TYPE"
	   "PRIORITY-QUEUE-TEST"
	   "ENQUEUE"
	   "DEQUEUE"
	   "QUEUE-EMPTY-P"
	   "QUEUE-SIZE"
	   )
  (:documentation "Implements a priority queue."))

(in-package :priority-queue)

(defclass priority-queue ()
  ((element-type :initarg :element-type 
		 :initform 'fixnum 
		 :accessor priority-queue-element-type 
		 :type symbol
		 :documentation "Element type stored in this queue.")
   (test :initarg :test 
	 :accessor priority-queue-test
	 :documentation "The partial order used in element comparison.")
   (heap :documentation "A private slot holding the heap."))
  (:documentation "Representa a priority queue based on heaps. 
Slots HEAP and TEST are read-only after they are initialized."))


(defmethod initialize-instance :around ((self priority-queue) 
				       &key 
					 (test #'<=)
					 (element-key #'identity))
  "Fill in the HEAP slot with an instance of a heap. NOTE: This has to
be an :AROUND method, so that the slot ELEMENT-TYPE can be initialized
in a :BEFORE or :AFTER method of a subclass of PRIORITY-QUEUE."
  (with-slots (heap (test-x test) element-type)
      (call-next-method)
    (setf heap (make-heap :element-type element-type)
	  test-x #'(lambda (x y) (funcall test (funcall element-key y) (funcall element-key x)))))
  self)
  
(defgeneric enqueue (self item)
  (:method ((self priority-queue) (item t))
    (with-slots (heap test)
	self
      (heap-insert heap item test))
    self))

(defgeneric dequeue (self)
  (:method ((self priority-queue))
    (with-slots (heap test)
	self
      (heap-remove heap test))))

(defgeneric queue-empty-p (self)
  (:method ((self priority-queue))
    (with-slots (heap)
	self
      (heap-empty-p heap))))

(defgeneric queue-size (self)
  (:method ((self priority-queue))
    (with-slots (heap)
	self
    (heap-size heap))))