NestedStackParameters.py

"""
Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
SPDX-License-Identifier: MIT-0
"""
import os
import six
from cfnlint.decode import decode
from cfnlint.rules import CloudFormationLintRule
from cfnlint.rules import RuleMatch


class NestedStackParameters(CloudFormationLintRule):
    """Check that nested stack parameters are specified as needed"""
    id = 'E3043'
    shortdesc = 'Validate parameters for in a nested stack'
    description = 'Evalute if parameters for a nested stack are specified and ' \
                  'if parameters are specified for a nested stack that aren\'t required.'
    source_url = 'https://github.com/awslabs/cfn-python-lint'
    tags = ['resources', 'cloudformation']

    def __init__(self):
        """Init"""
        super(NestedStackParameters, self).__init__()
        self.resource_property_types.append('AWS::CloudFormation::Stack')


    def __get_template_parameters(self, filename):

        try:
            (tmp, matches) = decode(filename)
        except:  #pylint: disable=bare-except
            return None
        if matches:
            return None

        return tmp.get('Parameters', {})


    def __compare_objects(self, template_parameters, nested_parameters, scenario, path):
        matches = []
        for key in set(template_parameters.keys()) - set(nested_parameters.keys()):
            if scenario is None:
                message = 'Specified parameter "{0}" doesn\'t exist in nested stack template at {1}'
                matches.append(
                    RuleMatch(path + [key], message.format(key, '/'.join(map(str, path + [key])))))
            else:
                message = 'Specified parameter "{0}" doesn\'t exist in nested stack template {1}'
                scenario_text = ' and '.join(
                    ['when condition "%s" is %s' % (k, v) for (k, v) in scenario.items()])
                matches.append(
                    RuleMatch(path, message.format(key, scenario_text)))
        for key in set(nested_parameters.keys())- set(template_parameters.keys()):
            if nested_parameters.get(key).get('Default') is None:
                if scenario is None:
                    message = 'Nested stack template parameter "{0}" is not specified at {1}'
                    matches.append(
                        RuleMatch(path, message.format(key, '/'.join(map(str, path)))))
                else:
                    message = 'Nested stack template parameter "{0}" is not specified {1}'
                    scenario_text = ' and '.join(
                        ['when condition "%s" is %s' % (k, v) for (k, v) in scenario.items()])
                    matches.append(
                        RuleMatch(path, message.format(key, scenario_text)))

        return matches


    def match_resource_properties(self, properties, _, path, cfn):
        """Check CloudFormation Properties"""
        matches = []

        # when template is passed via cat (or equivalent filename is none)
        if cfn.filename:
            base_dir = os.path.dirname(os.path.abspath(cfn.filename))

            parameter_groups = cfn.get_object_without_conditions(obj=properties, property_names=['TemplateURL', 'Parameters'])
            for parameter_group in parameter_groups:
                obj = parameter_group.get('Object')
                template_url = obj.get('TemplateURL')
                if isinstance(template_url, six.string_types):
                    if not (template_url.startswith('http://') or template_url.startswith('https://') or template_url.startswith('s3://')):
                        template_path = os.path.normpath(os.path.join(base_dir, template_url))
                        nested_parameters = self.__get_template_parameters(template_path)
                        template_parameters = obj.get('Parameters')
                        if isinstance(nested_parameters, dict) and isinstance(template_parameters, dict):
                            matches.extend(
                                self.__compare_objects(
                                    template_parameters=template_parameters,
                                    nested_parameters=nested_parameters,
                                    path=path + ['Parameters'],
                                    scenario=parameter_group.get('Scenario'),
                                )
                            )

        return matches