feat: widgets interface

Widgets are reusable jinja templates which can be used in other
themplates. Widgets are written in widgets/ directory in every frappe
module and can be accessed as `{{ widgets.WidgetName(...) }}` from any
template.

community/hooks.py

@@ -169,3 +169,5 @@ profile_rules = [
 ]
 
 website_route_rules = primary_rules + whitelist_rules + profile_rules
+
+update_website_context = 'community.widgets.update_website_context'

community/lms/widgets/HelloWorld.html

@@ -0,0 +1,14 @@
+{#
+  Widget to demonostrate how to write a widget.
+
+  A wiget is a reusable template, that can be used in
+  other templates.
+
+  To this widget can be called as:
+
+    {{ widgets.HelloWorld(name="World") }}
+#}
+
+<div class="hello">
+  Hello, <em>{{ name }}</em>!
+</div>

community/test_widgets.py

@@ -0,0 +1,16 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2021, FOSS United and Contributors
+# See license.txt
+import frappe
+import unittest
+from .widgets import Widget, Widgets
+
+class TestWidgets(unittest.TestCase):
+    def test_Widgets(self):
+        widgets = Widgets()
+        assert widgets.Foo.name == "Foo"
+        assert widgets.Bar.name == "Bar"
+
+    def _test_Widget(self):
+        hello = Widget("HelloWorld")
+        assert hello(name="Test") == "Hello, Test"

community/widgets.py

@@ -0,0 +1,60 @@
+"""The widgets provides access to HTML widgets
+provided in each frappe module.
+
+Widgets are simple moduler templates that can reused
+in multiple places. These are like macros, but accessing
+them will be a lot easier.
+
+The widgets will be provided
+"""
+import frappe
+from frappe.utils.jinja import get_jenv
+
+# search path for widgets.
+# When {{widgets.SomeWidget()}} is called, it looks for
+# widgets/SomeWidgets.html in each of these modules.
+MODULES = [
+    "lms"
+]
+
+def update_website_context(context):
+    """Adds widgets to the context.
+
+    Called from hooks.
+    """
+    context.widgets = Widgets()
+
+class Widgets:
+    """The widget collection.
+
+    This is just a placeholder object and returns the appropriate
+    widget when accessed using attribute.
+
+        >>> widgets = Widgets()
+        >>> widgets.HelloWorld(name="World!")
+        '<div>Hello, World!</div>'
+    """
+    def __getattr__(self, name):
+        if not name.startswith("__"):
+            return Widget(name)
+        else:
+            raise AttributeError(name)
+
+class Widget:
+    """The Widget class renders a widget.
+
+    Widget is a reusable template defined in widgets/ directory in
+    each frappe module.
+
+        >>> w = Widget("HelloWorld")
+        >>> w(name="World!")
+        '<div>Hello, World!</div>'
+    """
+    def __init__(self, name):
+        self.name = name
+
+    def __call__(self, **kwargs):
+        # the widget could be in any of the modules
+        paths = [f"{module}/widgets/{self.name}.html" for module in MODULES]
+        env = get_jenv()
+        return env.get_or_select_template(paths).render(kwargs)