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


class DependsOnObsolete(CloudFormationLintRule):
    """Check unneeded DepensOn Resource Configuration"""

    id = "W3005"
    shortdesc = "Check obsolete DependsOn configuration for Resources"
    description = (
        "Check if DependsOn is specified if not needed. "
        "A Ref or a Fn::GetAtt already is an implicit dependency."
    )
    source_url = (
        "https://aws.amazon.com/blogs/devops/optimize-aws-cloudformation-templates/"
    )
    tags = ["resources", "dependson", "ref", "getatt"]

    def get_resource_references(self, cfn, ref_function, resource):
        """Get tree of all resource references of a resource"""
        trees = cfn.search_deep_keys(ref_function)

        # Filter only resoureces
        trees = filter(lambda x: x[0] == "Resources", trees)
        # Filter on the given resource only
        trees = filter(lambda x: x[1] == resource, trees)

        return trees

    def check_depends_on(self, cfn, resource, key, path):
        """Check if the DependsOn is already specified"""
        matches = []

        # Get references
        trees = self.get_resource_references(cfn, "Ref", resource)

        for tree in trees:
            if tree[-1] == key:
                message = 'Obsolete DependsOn on resource ({0}), dependency already enforced by a "Ref" at {1}'
                matches.append(
                    RuleMatch(path, message.format(key, "/".join(map(str, tree[:-1]))))
                )

        # Get the GetAtt
        trees = self.get_resource_references(cfn, "Fn::GetAtt", resource)

        for tree in trees:
            # GettAtt formation is "resource : Attribute", just check the resource
            if tree[-1][0] == key:
                message = 'Obsolete DependsOn on resource ({0}), dependency already enforced by a "Fn:GetAtt" at {1}'
                matches.append(
                    RuleMatch(path, message.format(key, "/".join(map(str, tree[:-1]))))
                )

        return matches

    def match(self, cfn):
        matches = []

        resources = cfn.get_resources()

        for resource_name, resource_values in resources.items():
            depends_ons = resource_values.get("DependsOn")
            if depends_ons:
                path = ["Resources", resource_name, "DependsOn"]
                self.logger.debug("Validating unneeded DependsOn for %s", resource_name)
                if isinstance(depends_ons, list):
                    for index, depends_on in enumerate(depends_ons):
                        matches.extend(
                            self.check_depends_on(
                                cfn, resource_name, depends_on, path[:] + [index]
                            )
                        )
                else:
                    matches.extend(
                        self.check_depends_on(cfn, resource_name, depends_ons, path)
                    )

        return matches
