Implement a registry for rich text features

wagtail/tests/testapp/wagtail_hooks.py

@@ -90,3 +90,11 @@ def polite_pages_only(parent_page, pages, request):
         pages = pages.filter(slug__startswith='hello')
 
     return pages
+
+
+# register 'blockquote' as a rich text feature supported by a hallo.js plugin
+@hooks.register('register_rich_text_features')
+def register_blockquote_feature(features):
+    features.register_editor_plugin(
+        'hallo', 'blockquote', {'plugin_name': 'halloblockquote'}
+    )

wagtail/wagtailcore/rich_text.py

@@ -202,3 +202,46 @@ class RichText(object):
     def __bool__(self):
         return bool(self.source)
     __nonzero__ = __bool__
+
+
+class FeatureRegistry(object):
+    """
+    A central store of information about optional features that can be enabled in rich text
+    editors by passing a ``features`` list to the RichTextField, such as how to
+    whitelist / convert HTML tags, and how to enable the feature on various editors.
+
+    This information may come from diverse sources - for example, wagtailimages might define
+    an 'images' feature and a hallo.js plugin for it, while a third-party module might
+    define a TinyMCE plugin for the same feature. The information is therefore collected into
+    this registry via the 'register_rich_text_features' hook.
+    """
+    def __init__(self):
+        # Has the register_rich_text_features hook been run for this registry?
+        self.has_scanned_for_features = False
+
+        # a dict of dicts, one for each editor (hallo.js, TinyMCE etc); each dict is a mapping
+        # of feature names to 'plugin' objects that define how to implement that feature
+        # (e.g. paths to JS files to import). The API of that plugin object is not defined
+        # here, and is specific to each editor.
+        self.plugins_by_editor = {}
+
+    def _scan_for_features(self):
+        for fn in hooks.get_hooks('register_rich_text_features'):
+            fn(self)
+        self.has_scanned_for_features = True
+
+    def register_editor_plugin(self, editor_name, feature_name, plugin):
+        plugins = self.plugins_by_editor.setdefault(editor_name, {})
+        plugins[feature_name] = plugin
+
+    def get_editor_plugin(self, editor_name, feature_name):
+        if not self.has_scanned_for_features:
+            self._scan_for_features()
+
+        try:
+            return self.plugins_by_editor[editor_name][feature_name]
+        except KeyError:
+            return None
+
+
+features = FeatureRegistry()

wagtail/wagtailcore/tests/test_rich_text.py

@@ -6,7 +6,7 @@ from mock import patch
 
 from wagtail.wagtailcore.models import Page
 from wagtail.wagtailcore.rich_text import (
-    DbWhitelister, PageLinkHandler, RichText, expand_db_html, extract_attrs)
+    DbWhitelister, FeatureRegistry, PageLinkHandler, RichText, expand_db_html, extract_attrs)
 
 
 class TestPageLinkHandler(TestCase):
@@ -144,3 +144,21 @@ class TestRichTextValue(TestCase):
 
         value = RichText('<p>wagtail</p>')
         self.assertTrue(value)
+
+
+class TestFeatureRegistry(TestCase):
+    def test_register_rich_text_features_hook(self):
+        # testapp/wagtail_hooks.py defines a 'blockquote' rich text feature with a hallo.js
+        # plugin, via the register_rich_text_features hook; test that we can retrieve it here
+        features = FeatureRegistry()
+        blockquote = features.get_editor_plugin('hallo', 'blockquote')
+        self.assertEqual(blockquote['plugin_name'], 'halloblockquote')
+
+    def test_missing_editor_plugin_returns_none(self):
+        features = FeatureRegistry()
+        self.assertIsNone(
+            features.get_editor_plugin('made_up_editor', 'blockquote')
+        )
+        self.assertIsNone(
+            features.get_editor_plugin('hallo', 'made_up_feature')
+        )