added url handlebars helper

closes #528

- adds method (isPost)to models index.js that returns true if content, content_raw, title and slug are valid properties
- adds url helper which checks context is post using  isPost method
- adds unit test to check a url is prefixed with  /
-adds unit test which checks for empty string if either of the 4 properties above are not present.

core/server/helpers/index.js

@@ -4,8 +4,10 @@ var _ = require('underscore'),
     when = require('when'),
     hbs = require('express-hbs'),
     errors = require('../errorHandling'),
+    models = require('../models'),
     coreHelpers;
 
+
 coreHelpers = function (ghost) {
     var navHelper,
         paginationHelper;
@@ -29,6 +31,12 @@ coreHelpers = function (ghost) {
         return date;
     });
 
+    ghost.registerThemeHelper('url', function (context, options) {
+        if (models.isPost(this)) {
+            return "/" + this.slug;
+        }
+        return '';
+    });
 
     // ### Author Helper
     // 

core/server/models/index.js

@@ -13,5 +13,9 @@ module.exports = {
         return migrations.reset().then(function () {
             return migrations.init();
         });
+    },
+    isPost: function (jsonData) {
+        return jsonData.hasOwnProperty("content") && jsonData.hasOwnProperty("content_raw")
+            && jsonData.hasOwnProperty("title") && jsonData.hasOwnProperty("slug");
     }
 };

core/test/unit/frontend_helpers_index_spec.js

@@ -201,6 +201,25 @@ describe('Core Helpers', function () {
         });
     });
 
+    describe('url Helper', function () {
+        it('has loaded url helper', function () {
+            should.exist(handlebars.helpers.url);
+        });
+
+        it('if context is post, returns a the slug with a prefix slash', function () {
+            var rendered = handlebars.helpers.url.call({content: 'content', content_raw: "ff", title: "title", slug: "slug"});
+            should.exist(rendered);
+            rendered.should.equal('/slug');
+        });
+
+        it('it should return empty string if not a post', function () {
+            handlebars.helpers.url.call({content_raw: "ff", title: "title", slug: "slug"}).should.equal('');
+            handlebars.helpers.url.call({content: 'content', title: "title", slug: "slug"}).should.equal('');
+            handlebars.helpers.url.call({content: 'content', content_raw: "ff", slug: "slug"}).should.equal('');
+            handlebars.helpers.url.call({content: 'content', content_raw: "ff", title: "title"}).should.equal('');
+        });
+    });
+
     describe('Navigation Helper', function () {
 
         it('has loaded nav helper', function () {