# 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.

import json
import yaml

if hasattr(yaml, 'CSafeLoader'):
    yaml_loader = yaml.CSafeLoader
else:
    yaml_loader = yaml.SafeLoader


class HeatYamlLoader(yaml_loader):
    pass


def _construct_yaml_str(self, node):
    # Override the default string handling function
    # to always return unicode objects
    return self.construct_scalar(node)
HeatYamlLoader.add_constructor(u'tag:yaml.org,2002:str', _construct_yaml_str)
# Unquoted dates like 2013-05-23 in yaml files get loaded as objects of type
# datetime.data which causes problems in API layer when being processed by
# openstack.common.jsonutils. Therefore, make unicode string out of timestamps
# until jsonutils can handle dates.
HeatYamlLoader.add_constructor(
    u'tag:yaml.org,2002:timestamp', _construct_yaml_str)


def parse(tmpl_str):
    """Takes a string and returns a dict containing the parsed structure.

    This includes determination of whether the string is using the
    JSON or YAML format.
    """
    # strip any whitespace before the check
    tmpl_str = tmpl_str.strip()
    if tmpl_str.startswith('{'):
        tpl = json.loads(tmpl_str)
    else:
        try:
            tpl = yaml.load(tmpl_str, Loader=HeatYamlLoader)
        except yaml.YAMLError:
            # NOTE(prazumovsky): we need to return more informative error for
            # user, so use SafeLoader, which return error message with template
            # snippet where error has been occurred.
            try:
                tpl = yaml.load(tmpl_str, Loader=yaml.SafeLoader)
            except yaml.YAMLError as yea:
                raise ValueError(yea)
        else:
            if tpl is None:
                tpl = {}
    # Looking for supported version keys in the loaded template
    if not ('HeatTemplateFormatVersion' in tpl
            or 'heat_template_version' in tpl
            or 'AWSTemplateFormatVersion' in tpl):
        raise ValueError("Template format version not found.")
    return tpl
