jinja_utils.py

# Copyright 2014 The Oppia Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS-IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Jinja-related utilities."""

from __future__ import absolute_import  # pylint: disable=import-only-modules
from __future__ import unicode_literals  # pylint: disable=import-only-modules

import copy
import json
import logging
import math

import jinja2
from jinja2 import meta

import python_utils  # isort:skip


def _js_string_filter(value):
    """Converts a value to a JSON string for use in JavaScript code.

    Args:
        value: *. The specified value to be coverted to JSON string.

    Returns:
        str. The resulting JSON string.
    """
    string = json.dumps(value)

    replacements = [('\\', '\\\\'), ('"', '\\"'), ('\'', '\\\''),
                    ('\n', '\\n'), ('\r', '\\r'), ('\b', '\\b'),
                    ('<', '\\u003c'), ('>', '\\u003e'), ('&', '\\u0026')]

    for replacement in replacements:
        string = string.replace(replacement[0], replacement[1])
    return jinja2.utils.Markup(string)


def _log2_floor_filter(value):
    """Returns the logarithm base 2 of the given value, rounded down.

    Args:
        value: int|float. The specified value.

    Returns:
        int. The rounded off value of logarithm base 2 of the given value.
    """
    return int(math.log(value, 2))


JINJA_FILTERS = {
    'is_list': lambda x: isinstance(x, list),
    'is_dict': lambda x: isinstance(x, dict),
    'js_string': _js_string_filter,
    'log2_floor': _log2_floor_filter,
}


def parse_string(string, params, autoescape=True):
    """Parses a string using Jinja templating.

    Args:
        string: str. The string to be parsed.
        params: dict(str, *). The parameters to parse the string with.
        autoescape: bool. Whether to enable autoescaping when parsing.

    Returns:
        str. The string parsed using Jinja templating. Returns an error string
        in case of error in parsing.

    Raises:
        Exception. Unable to parse string with Jinja.
    """
    env = jinja2.Environment(autoescape=autoescape)

    env.filters.update(JINJA_FILTERS)
    try:
        parsed_string = env.parse(string)
    except Exception:
        raise Exception('Unable to parse string with Jinja: %s' % string)

    variables = meta.find_undeclared_variables(parsed_string)
    if any([var not in params for var in variables]):
        logging.info('Cannot parse %s fully using %s', string, params)

    try:
        return env.from_string(string).render(params)
    except Exception:
        logging.error(
            'jinja_utils.parse_string() failed with args: %s, %s, %s' %
            (string, params, autoescape))
        return env.from_string('[CONTENT PARSING ERROR]').render({})


def evaluate_object(obj, params):
    """Returns a copy of `obj` after parsing strings in it using `params`.

    Args:
        obj: *. An object containing strings that need to be parsed.
        params: dict(str, *). The parameters to parse the string with.

    Returns:
        *. The copy of `obj` after parsing strings in it.
    """

    if isinstance(obj, python_utils.BASESTRING):
        return parse_string(obj, params)
    elif isinstance(obj, list):
        new_list = []
        for item in obj:
            new_list.append(evaluate_object(item, params))
        return new_list
    elif isinstance(obj, dict):
        new_dict = {}
        for key in obj:
            new_dict[key] = evaluate_object(obj[key], params)
        return new_dict
    else:
        return copy.deepcopy(obj)