(defpackage inventory
  (:use :cl)
  (:export :inventory
		   :add-item
		   :remove-item))

(in-package :inventory)


(defclass inventory ()
  ((size :initarg :size
		 :reader size)
   (filled :initform 0
		   :accessor filled)
   (items :initform '()
    	  :accessor items)))

(defmethod find-item ((inv inventory) name)
  (with-slots (items) inv
	(find-if
	 #'(lambda (i)
		 (equal (commodities:name (car i)) name))
	 items)))

(defmethod delete-item ((inv inventory) item)
  ;; removes <item> from inventory list and substracts
  ;; its stored quantity from the filled attribute
  (with-slots (filled items) inv
	(setq items (remove item items))
	(setq filled (- filled (cdr item)))))

(defmethod add-item ((inv inventory) item quantity)
  ;; add <quantity> of <item> to inventory
  (with-slots (size filled items) inv
	(when (> size (+ filled quantity))
	  (let* ((old-item
			  (find-item inv (commodities:name item)))
			 (qt (if old-item
					 (progn
					   (delete-item inv old-item)
					   (+ quantity (cdr old-item)))
					 quantity)))
		(prog1
		  (setq filled (+ filled qt))
		  (push (cons item qt)
				items))))))

(defmethod remove-item ((inv inventory) name quantity)
  ;; remove <quantity> of <item> from inventory
  ;; quantity must be positive or zero
  (assert (>= quantity 0))
  (with-slots (filled items) inv
	(let ((item (find-item inv name)))
	  (when item
		(delete-item inv item)
	    (if (< quantity (cdr item))
			(progn
			  (add-item inv
						(car item)
						(- (cdr item) quantity))
			  (cons (car item) quantity))
			item)))))