(defn retrieve
  "Retrieve value with key from cache."
  [cache key]
  ;; search in the cache for the key, and write the returned value in 'value'
  ;; dosync needed, because cache tree needs to be updated if the element is found in the tree
  ;; so we need to make sure no other updates happen between find with splaying and updating
  (let [value (dosync
  				(let [newTree (st/find (:tree @cache) key)]
  					(if (= newTree nil)
  						nil
  						;;else
  						(do
  							(ref-set cache {:store (:store @cache) :maxSize (:maxSize @cache) :size (:size @cache) :tree newTree })
							(:value newTree)
						)
					)
				)
			   )
  		]

	(if (= value nil)
		;; if the value == nil, search in store for the key and write the returned value in storeValue
		(let [ storeValue (store/retrieve (:store @cache) key) ]

		  (if (= storeValue nil)
		    ;; if storeValue == nil, just return it
		    storeValue
		    ;; else check if maxSize == 0
		    (if (= (:maxSize @cache) 0)
		    	;;if maxSize == 0 just return the StoreValue
		    	storeValue
		    	;; else update cache and return the storeValue
			    (do
			    	(dosync
						(commute cache updatecache key storeValue)
					)
			    	;; return storeValue
					storeValue
			    )
			)
		 )
		)
		;; else return the value
		value

	)
  )
)