add support for rendering templates from files

src/clj_jtwig/core.clj

@@ -1,15 +1,40 @@
 (ns clj-jtwig.core
-  (:require [clojure.walk :refer [stringify-keys]])
-  (:import (com.lyncode.jtwig JtwigTemplate JtwigContext)))
+  (:require [clojure.walk :refer [stringify-keys]]
+            [clojure.java.io :as io])
+  (:import (com.lyncode.jtwig JtwigTemplate JtwigContext)
+           (java.io File)))
 
-(defn render
-  "renders a template contained in the provided string, using the values in model-map
-   as the model for the template."
-  [s model-map & {:keys [skip-model-map-stringify?] :as options}]
-  (let [template (new JtwigTemplate s)
-        context  (new JtwigContext)]
+(defn- get-resource-path [filename]
+  (-> (Thread/currentThread)
+      (.getContextClassLoader)
+      (.getResource filename)))
+
+(defn- render-template
+  [template model-map & [{:keys [skip-model-map-stringify?] :as options}]]
+  (let [context (new JtwigContext)]
     (doseq [[k v] (if-not skip-model-map-stringify?
                     (stringify-keys model-map)
                     model-map)]
       (.set context k v))
     (.output template context)))
+
+(defn render
+  "renders a template contained in the provided string, using the values in model-map
+   as the model for the template."
+  [s model-map & [options]]
+  (let [template (new JtwigTemplate s)]
+    (render-template template model-map options)))
+
+(defn render-file
+  "renders a template from a file, using the values in model-map as the model for the template"
+  [filename model-map & [options]]
+  (let [file     (new File filename)
+        template (new JtwigTemplate file)]
+    (render-template template model-map options)))
+
+(defn render-resource
+  "renders a template from a resource file, using the values in the model-map as the model for
+   the template."
+  [filename model-map & [options]]
+  (if-let [resource-filename (get-resource-path filename)]
+    (render-file (.getPath resource-filename) model-map options)))