Allow provider to override template_name and context

Also an example provider which renders the user's initals against
a randomly colored background.

avatar/providers.py

@@ -82,3 +82,26 @@ class FacebookAvatarProvider(object):
                 fb_id=fb_id,
                 size=size
             )
+
+
+class InitialsAvatarProvider:
+    """
+    Returns a tuple with template_name and context for rendering the given user's avatar as their
+    initials in white against a background with random hue based on their primary key.
+    """
+
+    def get_avatar_url(user, size):
+        initials = user.first_name[:1] + user.last_name[:1]
+        if not initials:
+            initials = user.username[:1]
+        initials = initials.upper()
+        context = {
+            'fontsize': (size*1.1)/2,
+            'initials': initials,
+            'hue': user.pk % 360,
+            'saturation': '65%',
+            'lightness': '60%',
+        }
+        return ('avatar/initials.html', context)
+
+

avatar/templates/avatar/initials.html

@@ -0,0 +1,12 @@
+<span style='background-color: hsla({{ hue }}, {{ saturation }}, {{ lightness }}, 1);
+             width: {{ size }}px;
+             height: {{ size }}px;
+             font-size: {{ fontsize }}px;
+             text-align: center;
+             color: white;
+             display: inline-block;
+             line-height: {{ size }}px;
+             {{ kwargs.style }}'
+      {% for key, value in kwargs.items %}{% if key != 'style' %}{{ key }}="{{ value }}" {% endif %}{% endfor %}>
+  {{ initials }}</span>
+

avatar/templatetags/avatar_tags.py

@@ -44,12 +44,19 @@ def avatar(user, size=settings.AVATAR_DEFAULT_SIZE, **kwargs):
         url = avatar_url(user, size)
     context = {
         'user': user,
-        'url': url,
         'alt': alt,
         'size': size,
         'kwargs': kwargs,
     }
-    return render_to_string('avatar/avatar_tag.html', context)
+    template_name = 'avatar/avatar_tag.html'
+    ext_context = None
+    try:
+        template_name, ext_context = url
+    except ValueError:
+        context['url'] = url
+    if ext_context:
+        context = dict(context, **ext_context)
+    return render_to_string(template_name, context)
 
 
 @register.filter