Add GET /item/:id endpoint

This new endpoint was so easy to add, it would have been a shame not to
do it. Besides, it makes sense since the reponse from `POST /items`
provided a `Location` header for the newly created item.

src/yohoho/core.clj

@@ -64,6 +64,14 @@
   {:status 200
    :body "Ahoy mate, the ship be sailin' alright"})
 
+(defn get-item-handler
+  [request]
+  (let [id (get-in request [:path-params :id])
+        item (db-get-item id)]
+    (cond
+      (nil? item) {:status 404 :body {:error "Not Found"}}
+      :else       {:status 200 :body item})))
+
 (defn get-items-handler
   [_]
   {:status 200
@@ -100,10 +108,11 @@
 (def app
   (ring/ring-handler
    (ring/router
-    [["/ahoy"  {:get ahoy-handler}]
-     ["/items" {:get get-items-handler
-                :post {:handler create-item-handler
-                       :parameters {:body Item}}}]]
+    [["/ahoy"     {:get ahoy-handler}]
+     ["/item/:id" {:get get-item-handler}]
+     ["/items"    {:get get-items-handler
+                   :post {:handler create-item-handler
+                          :parameters {:body Item}}}]]
     ;; Middlewares:
     ;; - wrap-content-type-json: ensure POST routes are sent JSON payload
     ;; - muuntaja middleware to automatically decode JSON