From f7ba8716a54df030ba226afa67ede792c517417a Mon Sep 17 00:00:00 2001
From: Wesley Kerfoot <wjak56@gmail.com>
Date: Thu, 23 Aug 2012 20:05:44 -0400
Subject: [PATCH] added cacher

---
 cacher.rkt | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 cacher.rkt

diff --git a/cacher.rkt b/cacher.rkt
new file mode 100644
index 0000000..61d8b94
--- /dev/null
+++ b/cacher.rkt
@@ -0,0 +1,67 @@
+#lang racket
+
+(require (planet mordae/couchdb:1:11))
+;(require (planet dherman/json:4:0))
+
+(define (database-connection database-name)
+  (couchdb-db
+   (couchdb-connect
+   #:host "localhost"
+   #:port 5984
+   #:user "wes"
+   #:password "password")
+   database-name))
+
+(define conn (database-connection "blipcache"))
+
+(define (cached? id)
+  (with-handlers ([exn:couchdb:not-found?
+                   (lambda (_) 
+                     #f)])
+    (couchdb-get conn id)))
+
+;; type is the type of data to cache
+;; info is the actual name of the data to be cached
+;; get-data is the proc that gets the data from the database
+(define (cache info type get-data)
+  (match type
+    ['user 
+     (let* ([message (make-hash)]
+            [data (get-data)])
+       (hash-set! message '_id info)
+       (hash-set! message 'content data)
+       (hash-set! message 'last_updated (current-inexact-milliseconds))
+     (couchdb-put conn message)
+       data)]))
+
+;; Checks if a document needs updating
+;; Info -> String
+;; Data -> Hash
+;; Updater -> (Hash -> Hash)
+(define (update? info data updater)
+  (let* ([last-time (hash-ref data 'last_updated)]
+         [revision-id (hash-ref data '_rev)]
+         [current-time (current-inexact-milliseconds)]
+         [new-data (updater data)])
+    (match (> (- current-time last-time) 300000)
+    [#t (λ ()
+          (let ([message (hasheq '_rev revision-id
+                                 'last_updated current-time
+                                 'content new-data
+                                 '_id (hash-ref data '_id))])
+            (couchdb-put conn message)))]
+      [_ #f])))
+            
+          
+;((update? "foobar" (couchdb-get conn "foobar") (λ (h) (string-append "watwat" "foobarbaz"))))          
+                                   
+;; 
+(define (check-cache info type get-data)
+  (match (cached? info)
+    [#f (cache info type get-data)]
+    [result 
+     (match (update? info (couchdb-get conn info))
+       [#f result]
+       [updated (updated)])]))
+       
+(provide check-cache)
\ No newline at end of file