[per-object-permissions] Created template tag if_has_perm to check for a users permission

git-svn-id: http://code.djangoproject.com/svn/django/branches/per-object-permissions@3589 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/auth/templatetags/auth.py

@@ -0,0 +1,90 @@
+from django import template
+from django.template import loader
+
+register = template.Library()
+
+def if_has_perm(parser, token):
+    """
+
+    TODO: Update document
+    
+    Checks permission on the given user. Will check 
+    row level permissions if an object is given.
+    
+    Note: Perm name should be in the format of [app_label].[perm codename]
+        
+    """    
+    tokens = token.split_contents()
+    if len(tokens)<2:
+        raise template.TemplateSyntaxError, "%r tag requires at least 1 arguments" % tokens[0]
+    if len(tokens)>4:
+        raise template.TemplateSyntaxError, "%r tag should have no more then 3 arguments" % tokens[0]
+    
+    nodelist_true = parser.parse(('else', 'end_'+tokens[0],))
+    token = parser.next_token()
+    if token.contents == 'else':
+        nodelist_false = parser.parse(('end_'+tokens[0],))
+        parser.delete_first_token()
+    else:
+        nodelist_false = template.NodeList()
+    
+    object = None
+    not_flag = False
+    if tokens[1] is "not":
+        not_flag = True
+        permission=tokens[2]
+        if tokens[3]:
+            object=tokens[3]
+    else:
+        permission=tokens[1]
+        if tokens[2]:
+            object=tokens[2]
+
+    if not (permission[0] == permission[-1] and permission[0] in ('"', "'")):            
+        raise template.TemplateSyntaxError, "%r tag's argument should be in quotes" % tokens[0]
+            
+    return HasPermNode(permission[1:-1], not_flag, object, nodelist_true, nodelist_false)
+    
+class HasPermNode(template.Node):
+    def __init__(self, permission, not_flag, object, nodelist_true, nodelist_false):
+        self.permission = permission
+        self.not_flag = not_flag
+        self.object_name = object
+        self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false
+
+    def __repr__(self):
+        return "<HasPerm node>"
+
+    def __iter__(self):
+        for node in self.nodelist_true:
+            yield node
+        for node in self.nodelist_false:
+            yield node
+
+    def get_nodes_by_type(self, nodetype):
+        nodes = []
+        if isinstance(self, nodetype):
+            nodes.append(self)
+        nodes.extend(self.nodelist_true.get_nodes_by_type(nodetype))
+        nodes.extend(self.nodelist_false.get_nodes_by_type(nodetype))
+        return nodes
+
+    def render(self, context):
+        try:
+            object = template.resolve_variable(self.object_name, context)
+        except template.VariableDoesNotExist:
+            return ''
+        
+        try:
+            user = template.resolve_variable("user", context)
+        except template.VariableDoesNotExist:
+            return ''
+        
+        bool_perm = user.has_perm(self.permission, object=object)
+
+        if (self.not_flag and not bool_perm) or (not self.not_flag and bool_perm):
+            return self.nodelist_true.render(context)
+        if (self.not_flag and bool_perm) or (not self.not_flag and not bool_perm):
+            return self.nodelist_false.render(context)
+        
+register.tag('if_has_perm', if_has_perm)