Added support for image references (issue #74)

README.md

@@ -501,6 +501,17 @@ note: to enable footnotes, the `:footnotes?` option must be set to true.
 ![Alt text](/path/to/img.jpg "Optional Title")
 ```
 
+##### Image Reference
+
+```
+This is ![an example][id] reference-style image descriptor.
+
+[id]: http://example.com/  "Optional Title Here"
+```
+
+note: reference links require the `:reference-links?` option to be set to true
+
+
 ### Image Link
 ```
 [![Continuous Integration status](https://secure.travis-ci.org/yogthos/markdown-clj.png)](http://travis-ci.org/yogthos/markdown-clj)

src/cljc/markdown/links.cljc

@@ -133,11 +133,10 @@
     (if (nil? match)
       [text state]
       (let [next-text (string/replace-first text matcher (partial replace-footnote-link footnotes))
-            next-state
-                      (-> state
-                          (update-in [:footnotes :next-fn-id] inc)
-                          (assoc-in [:footnotes :processed (get-in state [:footnotes :next-fn-id])]
-                                    (get-in state [:footnotes :unprocessed match])))]
+            next-state (-> state
+                           (update-in [:footnotes :next-fn-id] inc)
+                           (assoc-in [:footnotes :processed (get-in state [:footnotes :next-fn-id])]
+                                     (get-in state [:footnotes :unprocessed match])))]
         (recur next-text next-state)))))
 
 (defn footnote-link [text {:keys [code codeblock footnotes] :as state}]
@@ -151,3 +150,21 @@
     :else
     (let [[text state] (replace-all-footnote-links text state)]
       [text state])))
+
+(defn make-image-reference [src alt title]
+  (let [title-text (str (if title (str "\" title=" (string/join title) "") "\""))]
+   (str "<img src=\"" src "\" alt=\"" alt title-text " />")))
+
+(defn image-reference-link [text {:keys [references] :as state}]
+  (if (or (not (:reference-links? state)) (empty? references))
+    [text state]
+    (let [matcher #"!\[([^\]]+)\]\s*(\[[a-zA-Z0-9 ]+\])"
+          matches (distinct (re-seq matcher text))]
+      (loop [ms matches
+             new-text text]
+        (if (seq ms)
+          (let [[m alt ref] (first ms)
+                refval (get references ref)
+                im (make-image-reference (first refval) alt (second refval))]
+            (recur (rest ms) (string/replace new-text m im)))
+          [new-text state])))))

src/cljc/markdown/transformers.cljc

@@ -4,6 +4,7 @@
              :refer [link
                      image
                      reference-link
+                     image-reference-link
                      implicit-reference-link
                      footnote-link]]
             [markdown.lists :refer [li]]
@@ -289,6 +290,7 @@
    autoemail-transformer
    autourl-transformer
    image
+   image-reference-link
    link
    implicit-reference-link
    reference-link

test/files/img_references.html

@@ -0,0 +1 @@
+<p>You can optionally use a space to separate the sets of brackets:</p><p>This is <img src="http://example.com/" alt="an example" title="Optional Title Here" /> reference-style image descriptor.</p><p>This is <img src="http://example.com/" alt="an example" title="Optional Title Here" /> reference-style image descriptor.</p><p>This is <img src="http://example.com/" alt="an example" title='Optional Title Here' /> reference-style image descriptor.</p><p>This is <img src="http://example.com/" alt="an/example" title='Optional Title Here' /> reference-style image descriptor.</p><p>This is <img src="http://example.com/" alt="an'example" title='Optional Title Here' /> reference-style image descriptor.</p><p>Then, anywhere in the document, you define your image descriptor label like this, on a line by itself:</p><p>This is <img src="http://example.com/" alt="an example" title=(Optional Title Here) /> reference-style image descriptor.</p><p>This is <img src="http://example.com/" alt="an example" /> reference-style image descriptor.</p><p>A image descriptor with <img src="http://example.com/#<i>a</i>b" alt="an underscore" />.</p>

test/files/img_references.md

@@ -0,0 +1,30 @@
+[id]: http://example.com/  "Optional Title Here"
+
+You can optionally use a space to separate the sets of brackets:
+
+This is ![an example] [id] reference-style image descriptor.
+
+This is ![an example][id] reference-style image descriptor.
+
+This is ![an example][id1] reference-style image descriptor.
+
+This is ![an/example][id1] reference-style image descriptor.
+
+This is ![an'example][id1] reference-style image descriptor.
+
+Then, anywhere in the document, you define your image descriptor label like this, on a line by itself:
+
+This is ![an example][id2] reference-style image descriptor.
+
+This is ![an example][id3] reference-style image descriptor.
+
+A image descriptor with ![an underscore][underscore].
+
+[id1]: http://example.com/  'Optional Title Here'
+
+[id2]: http://example.com/  (Optional Title Here)
+
+[id3]: http://example.com/
+
+[underscore]: http://example.com/#_a_b
+

test/markdown/md_file_test.clj

@@ -9,6 +9,13 @@
     (markdown/md-to-html (str "test/files" java.io.File/separator "references.md") wrt :reference-links? true)
     (is (= (slurp (str "test/files" java.io.File/separator "references.html")) (.toString wrt)))))
 
+(deftest img-references
+  (let [wrt (java.io.StringWriter.)]
+    (markdown/md-to-html (str "test/files" java.io.File/separator "img_references.md") wrt :reference-links? true)
+    (is (= (clojure.string/trim-newline
+            (slurp (str "test/files" java.io.File/separator "img_references.html")))
+           (.toString wrt)))))
+
 (deftest footnotes
   (let [wrt (java.io.StringWriter.)]
     (markdown/md-to-html (str "test/files" java.io.File/separator "footnotes.md") wrt :footnotes? true)