update imagine plugin to support captions

_plugins/image.rb

@@ -2,11 +2,49 @@
   module Tags
     class ImageTag < Liquid::Tag
       def render(context)
-        src = @markup.strip
-        baseurl = context.registers[:site].config['baseurl']
-        "<a href=\"#{baseurl}/images/#{src}\" target=\"_blank\" rel=\"lightbox\">
-            <img class=\"img-responsive img-thumbnail img-tag\" src=\"#{baseurl}/images/#{src}\" />
-        </a>"
+        if tag_contents = determine_arguments(@markup.strip)
+          src, caption = tag_contents[0], tag_contents[1]
+          baseurl = context.registers[:site].config['baseurl']
+          img_tag(src, baseurl, caption)
+        else
+          raise ArgumentError.new <<-eos
+  Syntax error in tag 'image' while parsing the following markup:
+  
+    #{@markup}
+  
+  Valid syntax:
+    for image: {% image icon.png %}
+    for image with caption: {% image icon.png This is a caption. %}
+  eos
+        end
+      end
+
+      private
+  
+      def determine_arguments(input)
+        matched = input.split(" ", 2)
+        if matched.length == 0
+          false
+        elsif matched.length > 1
+          [matched[0].to_s.strip, matched[1].to_s.strip]
+        else
+          [matched[0].to_s.strip, ""]
+        end
+      end
+
+      def img_tag(src, baseurl, caption = nil)
+        if caption.empty?
+          "<a href=\"#{baseurl}/images/#{src}\" target=\"_blank\" rel=\"lightbox\">
+             <img class=\"img-responsive img-thumbnail img-tag\" src=\"#{baseurl}/images/#{src}\" />
+          </a>"
+        else
+          "<figure>
+            <a href=\"#{baseurl}/images/#{src}\" target=\"_blank\" rel=\"lightbox\">
+              <img class=\"img-responsive img-thumbnail img-tag\" src=\"#{baseurl}/images/#{src}\" alt=\"#{caption}\" />
+            </a>
+            <figcaption>#{caption}</figcaption>
+          </figure>"
+        end
       end
     end
   end