# Copyright 2019 VyOS maintainers and contributors <maintainers@vyos.io>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library.  If not, see <http://www.gnu.org/licenses/>.

import os

from jinja2 import Environment
from jinja2 import FileSystemLoader

from vyos.defaults import directories


# reuse the same Environment to improve performance
_templates_env = Environment(loader=FileSystemLoader(directories['templates']))
_templates_mem = {}

def render(destination, template, content):
    """
    render a template from the template directory, it will raise on any errors
    destination: the file where the rendered template must be saved
    template: the path to the template relative to the template folder
    content: the dictionary to use to render the template

    This classes cache the renderer, so rendering the same file multiple time
    does not cause as too much overhead. If use everywhere, it could be changed
    and load the template from python environement variables from an import 
    python module generated when the debian package is build 
    (recovering the load time and overhead caused by having the file out of the code)
    """

    # Setup a renderer for the given template
    # This is cached and re-used for performance
    if template not in _templates_mem:
        _templates_mem[template] = _templates_env.get_template(template)
    template = _templates_mem[template]

    # As we are opening the file with 'w', we are performing the rendering
    # before calling open() to not accidentally erase the file if the 
    # templating fails
    content = template.render(content)

    # Write client config file
    with open(destination, 'w') as f:
        f.write(content)