feat: Add filterTransform option

* allow uesr to provide transformations which apply to the filter values
* make test more real-world :)
* fix syntax
* match formatting in docs
* use old school options defaulting
* add closing brace & indicate the need for non-JSON config
* clarify usage even more

docs/global-settings.md

@@ -50,3 +50,34 @@ For using the [Content Delivery API](https://www.contentful.com/developers/docs/
 
 *Recommended way here is to set the `host` in the `metalsmith.json` or global config and overwrite it if needed in depending source files.*
 
+### `filterTransforms` *(optional)*
+
+If you want to use dynamic values in a source file's filter query, you can provide an object containing named functions that will be invoked during the metalsmith build. For example, if you provide a configuration like this:
+
+```javascript
+{
+  // ...
+  filterTransforms: {
+    __NOW__() {
+      return (new Date()).toISOString();
+    },
+  },
+  // ...
+}
+```
+
+Note that you will need to invoke metalsmith programatically & process configuration as javascript, not JSON, in this case.
+
+You can then use the keyword `__NOW__` in your source file's `filter` values, like so:
+
+```markdown
+---
+title: Post overview of entries including "rabbit"
+contentful:
+  content_type: post
+  filter:
+    'startdate[lte]': '__NOW__'
+    'enddate[gt]': '__NOW__'
+layout: posts.html
+---
+```

docs/source-file-settings.md

@@ -296,4 +296,4 @@ POSTS-CONTENT-DIFFERENT-SPACE
 
 ## File meta available in template
 
-Contentful-metalsmith adds some [handy meta information](./file-meta.md) to the data available in data to make the generation of sites even easier.
+Contentful-metalsmith adds some [handy meta information](./file-meta.md) to the data available in data to make the generation of sites even easier.

lib/processor.js

@@ -114,7 +114,7 @@ function processFile (file, options) {
   const spaceId = file.contentful.space_id || options.space_id
   const accessToken = file.contentful.access_token || options.access_token
   const host = file.contentful.host || options.host
-  const query = util.getEntriesQuery(file.contentful)
+  const query = util.getEntriesQuery(file.contentful, options.filterTransforms)
 
   const client = getContentfulClient(accessToken, spaceId, host)
 

lib/util.js

@@ -29,12 +29,15 @@ function _slug (value) {
  * Get entries query
  *
  * @param {Object} options file meta options
+ * @param {Object} filterTransforms transformations for filter values
  *
  * @return {Object}        query obejct
  */
-function getEntriesQuery (options) {
+function getEntriesQuery (options, filterTransformsOptions) {
   const query = {}
 
+  const filterTransforms = filterTransformsOptions || {}
+
   if (options.content_type && options.content_type !== '*') {
     query.content_type = options.content_type
   }
@@ -44,6 +47,13 @@ function getEntriesQuery (options) {
   }
 
   if (options.filter) {
+    // If a transformation is available for this keyword, apply it.
+    for (let key in options.filter) {
+      if (typeof filterTransforms[options.filter[key]] === 'function') {
+        options.filter[key] = filterTransforms[options.filter[key]]()
+      }
+    }
+
     Object.assign(query, options.filter)
   }
 

lib/util.spec.js

@@ -28,6 +28,18 @@ test('util.getEntriesQuery - it should set given properties properly', t => {
   t.is(query.order, 'ASC')
 })
 
+test('util.getEntriesQuery - it should replace KEYWORD with the result of a function KEYWORD as defined in options.filterTransforms', t => {
+  const aCertainNow = new Date().toISOString()
+
+  let query = util.getEntriesQuery({ filter: { 'fields.startdate[lte]': '__NOW__' } }, {
+    __NOW__ () {
+      return aCertainNow
+    }
+  })
+
+  t.is(query['fields.startdate[lte]'], aCertainNow, 'filterTransforms correctly applied')
+})
+
 test('util.getFileName - should use the correct defaults', t => {
   const fileName = util.getFileName(
     {