macro.yaml

AWSTemplateFormatVersion: 2010-09-09
Description: CloudFormation Transformation Macros

Resources:
  LambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          -
            Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action:
              - sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

  EventRuleTargetsFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaRole.Arn
      Runtime: nodejs12.x
      Code:
        ZipFile: !Sub |
          'use strict';
          exports.handler = async (event) => {
            console.log(JSON.stringify(event));
            const resources = event.fragment.Resources;
            const resources_to_transform = Object.keys(resources).filter(r => resources[r].Type === 'AWS::Events::Rule' && !resources[r].Properties.Targets);
            resources_to_transform.forEach((r) => {
              resources[r].Properties.Targets = event.templateParameterValues.arns.map((a, index) => {
                return {
                  Arn: { 'Fn::Select': [index , { Ref: 'arns' } ] },
                  Id: a.split(':')[4] + '-' + a.split(':')[5].split('/')[1]
                };
              });
            });
            console.log(JSON.stringify(event.fragment));
            return {
              requestId: event.requestId,
              status: 'success',
              fragment: event.fragment
            };
          };

  EventRuleTargetsMacro:
    Type: AWS::CloudFormation::Macro
    Properties:
      Name: EventsRuleTargets
      FunctionName: !GetAtt EventRuleTargetsFunction.Arn