from django.core import template
from django.core.cache import cache
from django.conf import settings

class CachedNode(template.Node):
    """
    Cached template node.  
    
    Subclasses should define the methods ``get_cache_key()`` and
    ``get_content()`` instead of the standard render() method. Subclasses may
    also define the class attribute ``cache_timeout`` to override the default
    cache timeout of ten minutes.
    """
    
    cache_timeout = 600
    
    def render(self, context):
        if settings.DEBUG:
            return self.get_content(context)
        key = self.get_cache_key(context)
        content = cache.get(key)
        if not content:
            content = self.get_content(context)
            cache.set(key, content, self.cache_timeout)
        return content
        
    def get_cache_key(self, context):
        raise NotImplementedError()
        
    def get_content(self, context):
        raise NotImplementedError()
        
class ContextUpdatingNode(template.Node):
    """
    Node that updates the context with certain values.
    
    Subclasses should define ``get_content()``, which should return a dictionary
    to be added to the context.
    """
    
    def render(self, context):
        context.update(self.get_content(context))
        return ''
        
class CachedContextUpdatingNode(CachedNode, ContextUpdatingNode):
    """
    Node that updates the context, and is cached. Subclasses need to define
    ``get_cache_key()`` and ``get_content()``.
    """
    
    def render(self, context):
        context.update(CachedNode.render(self, context))
        return ''