from django.template import TemplateSyntaxError, TemplateDoesNotExist, Variable

from django.template import Library, Node, TextNode

from django.template.loader import get_template, get_template_from_string, find_template_source

from django.conf import settings

from django.utils.safestring import mark_safe

register = Library()

class ExtendsError(Exception):

    pass

class BlockNode(Node):

    def __init__(self, name, nodelist, parent=None):

        self.name, self.nodelist, self.parent = name, nodelist, parent

    def __repr__(self):

        return "<Block Node: %s. Contents: %r>" % (self.name, self.nodelist)

    def render(self, context):

        context.push()

        # Save context in case of block.super().

        self.context = context

        context['block'] = self

        result = self.nodelist.render(context)

        context.pop()

        return result

    def super(self):

        if self.parent:

            return mark_safe(self.parent.render(self.context))

        return ''

    def add_parent(self, nodelist):

        if self.parent:

            self.parent.add_parent(nodelist)

        else:

            self.parent = BlockNode(self.name, nodelist)

class ExtendsNode(Node):

    must_be_first = True

    def __init__(self, nodelist, parent_name, parent_name_expr, template_dirs=None):

        self.nodelist = nodelist

        self.parent_name, self.parent_name_expr = parent_name, parent_name_expr

        self.template_dirs = template_dirs

    def __repr__(self):

        if self.parent_name_expr:

            return "<ExtendsNode: extends %s>" % self.parent_name_expr.token

        return '<ExtendsNode: extends "%s">' % self.parent_name

    def get_parent(self, context):

        if self.parent_name_expr:

            self.parent_name = self.parent_name_expr.resolve(context)

        parent = self.parent_name

        if not parent:

            error_msg = "Invalid template name in 'extends' tag: %r." % parent

            if self.parent_name_expr:

                error_msg += " Got this from the '%s' variable." % self.parent_name_expr.token

            raise TemplateSyntaxError, error_msg

        if hasattr(parent, 'render'):

            return parent # parent is a Template object

        try:

            source, origin = find_template_source(parent, self.template_dirs)

        except TemplateDoesNotExist:

            raise TemplateSyntaxError, "Template %r cannot be extended, because it doesn't exist" % parent

        else:

            return get_template_from_string(source, origin, parent)

    def render(self, context):

        compiled_parent = self.get_parent(context)

        parent_blocks = dict([(n.name, n) for n in compiled_parent.nodelist.get_nodes_by_type(BlockNode)])

        for block_node in self.nodelist.get_nodes_by_type(BlockNode):

            # Check for a BlockNode with this node's name, and replace it if found.

            try:

                parent_block = parent_blocks[block_node.name]

            except KeyError:

                # This BlockNode wasn't found in the parent template, but the

                # parent block might be defined in the parent's *parent*, so we

                # add this BlockNode to the parent's ExtendsNode nodelist, so

                # it'll be checked when the parent node's render() is called.

                # Find out if the parent template has a parent itself

                for node in compiled_parent.nodelist:

                    if not isinstance(node, TextNode):

                        # If the first non-text node is an extends, handle it.

                        if isinstance(node, ExtendsNode):

                            node.nodelist.append(block_node)

                        # Extends must be the first non-text node, so once you find

                        # the first non-text node you can stop looking. 

                        break

            else:

                # Keep any existing parents and add a new one. Used by BlockNode.

                parent_block.parent = block_node.parent

                parent_block.add_parent(parent_block.nodelist)

                parent_block.nodelist = block_node.nodelist

        return compiled_parent.render(context)

class ConstantIncludeNode(Node):

    def __init__(self, template_path):

        try:

            t = get_template(template_path)

            self.template = t

        except:

            if settings.TEMPLATE_DEBUG:

                raise

            self.template = None

    def render(self, context):

        if self.template:

            return self.template.render(context)

        else:

            return ''

class IncludeNode(Node):

    def __init__(self, template_name):

        self.template_name = Variable(template_name)

    def render(self, context):

        try:

            template_name = self.template_name.resolve(context)

            t = get_template(template_name)

            return t.render(context)

        except TemplateSyntaxError, e:

            if settings.TEMPLATE_DEBUG:

                raise

            return ''

        except:

            return '' # Fail silently for invalid included templates.

def do_block(parser, token):

    """

    Define a block that can be overridden by child templates.

    """

    bits = token.contents.split()

    if len(bits) != 2:

        raise TemplateSyntaxError, "'%s' tag takes only one argument" % bits[0]

    block_name = bits[1]

    # Keep track of the names of BlockNodes found in this template, so we can

    # check for duplication.

    try:

        if block_name in parser.__loaded_blocks:

            raise TemplateSyntaxError, "'%s' tag with name '%s' appears more than once" % (bits[0], block_name)

        parser.__loaded_blocks.append(block_name)

    except AttributeError: # parser.__loaded_blocks isn't a list yet

        parser.__loaded_blocks = [block_name]

    nodelist = parser.parse(('endblock', 'endblock %s' % block_name))

    parser.delete_first_token()

    return BlockNode(block_name, nodelist)

def do_extends(parser, token):

    """

    Signal that this template extends a parent template.

    This tag may be used in two ways: ``{% extends "base" %}`` (with quotes)

    uses the literal value "base" as the name of the parent template to extend,

    or ``{% extends variable %}`` uses the value of ``variable`` as either the

    name of the parent template to extend (if it evaluates to a string) or as

    the parent tempate itelf (if it evaluates to a Template object).

    """

    bits = token.contents.split()

    if len(bits) != 2:

        raise TemplateSyntaxError, "'%s' takes one argument" % bits[0]

    parent_name, parent_name_expr = None, None

    if bits[1][0] in ('"', "'") and bits[1][-1] == bits[1][0]:

        parent_name = bits[1][1:-1]

    else:

        parent_name_expr = parser.compile_filter(bits[1])

    nodelist = parser.parse()

    if nodelist.get_nodes_by_type(ExtendsNode):

        raise TemplateSyntaxError, "'%s' cannot appear more than once in the same template" % bits[0]

    return ExtendsNode(nodelist, parent_name, parent_name_expr)

def do_include(parser, token):

    """

    Loads a template and renders it with the current context.

    Example::

        {% include "foo/some_include" %}

    """

    bits = token.contents.split()

    if len(bits) != 2:

        raise TemplateSyntaxError, "%r tag takes one argument: the name of the template to be included" % bits[0]

    path = bits[1]

    if path[0] in ('"', "'") and path[-1] == path[0]:

        return ConstantIncludeNode(path[1:-1])

    return IncludeNode(bits[1])

register.tag('block', do_block)

register.tag('extends', do_extends)

register.tag('include', do_include)