import pkg_resources
import templatetools

class ZPT(object):

    """
    You can access other templates with here/template_name (which is a
    name, potentially dotted, relative to the current template).  Or
    here/parent.parent.template_name (which is goes up two levels from
    the current template in this case)
    """

    def __init__(self, extra_vars_func=None, options=None):
        """The standard constructor takes an 'extra_vars_func',
        which is a callable that is called for additional
        variables with each rendering. Options is a dictionary
        that provides options specific to template engines
        (encoding, for example). The options should be
        prefixed with the engine's scheme name to allow the
        same dictionary to be passed in to multiple engines
        without ill effects."""
        self.extra_vars_func = extra_vars_func
        self.options = options or {}
        self._cached_templates = {}

    def load_template(self, templatename, relative_to=None):
        while templatename.startswith('parent.'):
            templatename = templatename[len('parent.'):]
            relative_to = '.'.join(relative_to.split('.')[:-1])
        if relative_to is not None:
            templatename = relative_to + '.' + templatename
        if templatename in self._cached_templates:
            template = self._cached_templates[templatename]
            template.refresh()
        else:
            parts = templatename.split('.')
            module = '.'.join(parts[:-1])
            base = parts[-1] + '.pt'
            filename = pkg_resources.resource_filename(module, base)
            here = templatetools.HereSpace(self.load_template, (module,))
            template = templatetools.FilePageTemplate(
                filename, here, **self.options)
        return template

    def render(self, info, format="html", fragment=False, template=None):
        "Renders the template to a string using the provided info."
        if self.extra_vars_func:
            info = info.copy()
            info.update(self.extra_vars_func())
        if isinstance(template, basestring):
            template = self.load_template(template)
        text = template(context=info)
        return text