# -*- coding: utf-8 -*-
"""

Jinja2 extension that adds support for caching template fragments.

Usage:
    {% cache timeout key1[, [key2, ...]] %}
    ...
    {% endcache %}

    By default the value of "path to template file" + "block start line" is used as cache key.
    Also key name can be set manually. Keys are concated together into a single string.
    that can be used to avoid the same block evaluating in different templates.

    Set timeout to "del" to delete cached value:
    {% cache 'del' key1 %}...

Example:
    Considering we have render_form_field and render_submit macros.
    {% cache 60*5 'myform' %}
    <div>
        <form>
        {% render_form_field form.username %}
        {% render_submit %}
        </form>
    </div>
    {% endcache %}

"""

from jinja2 import nodes
from jinja2.ext import Extension
from flask.ext.cache import make_template_fragment_key

JINJA_CACHE_ATTR_NAME = '_template_fragment_cache'


class CacheExtension(Extension):
    tags = set(['cache'])

    def parse(self, parser):
        lineno = next(parser.stream).lineno

        #: Parse timeout
        args = [parser.parse_expression()]

        #: Parse fragment name
        #: Grab the fragment name if it exists
        #: otherwise, default to the old method of using the templates
        #: lineno to maintain backwards compatibility.
        if parser.stream.skip_if('comma'):
            args.append(parser.parse_expression())
        else:
            args.append(nodes.Const("%s%s" % (parser.filename, lineno)))

        #: Parse vary_on parameters
        vary_on = []
        while parser.stream.skip_if('comma'):
            vary_on.append(parser.parse_expression())

        if vary_on:
            args.append(nodes.List(vary_on))
        else:
            args.append(nodes.Const([]))

        body = parser.parse_statements(['name:endcache'], drop_needle=True)
        return nodes.CallBlock(self.call_method('_cache', args),
                               [], [], body).set_lineno(lineno)

    def _cache(self, timeout, fragment_name, vary_on,  caller):
        try:
            cache = getattr(self.environment, JINJA_CACHE_ATTR_NAME)
        except AttributeError as e:
            raise e

        key = make_template_fragment_key(fragment_name, vary_on=vary_on)

        #: Delete key if timeout is 'del'
        if timeout == "del":
            cache.delete(key)
            return caller()

        rv = cache.get(key)
        if rv is None:
            rv = caller()
            cache.set(key, rv, timeout)
        return rv