AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Streams DynamoDB table changes to EventBridge
Resources:
  #DynamoDB Streams specification
  MyDynamoStream:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      AttributeDefinitions:
        - AttributeName: name
          AttributeType: S
      KeySchema:
        - AttributeName: name
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: 5
        WriteCapacityUnits: 5
      StreamSpecification:
          StreamViewType: NEW_AND_OLD_IMAGES

  # Define the publisher Lambda function with permissions
  EventProcessingFunction:
    Type: 'AWS::Serverless::Function'
    Properties:
      Handler: app.handler
      Runtime: nodejs14.x
      CodeUri: publish/
      Description: A Lambda function that forward changes on DynamoDB table to EventBridge bus.
      MemorySize: 128
      Timeout: 3
      Events:
        TableRecordChange:
          Type: DynamoDB
          Properties:
            StartingPosition: LATEST
            Stream: !GetAtt MyDynamoStream.StreamArn
      Policies:
        - Statement:
          - Effect: Allow
            Resource: '*'
            Action:
              - events:PutEvents
  
  #Define the Lambda subscribers for INSERT and REMOVE events from table
  SubscribeInsertFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: subscribe/
      Handler: app.handler
      Runtime: nodejs14.x
      Description: A Lambda function that receive Insert events from the table.
      MemorySize: 128
      Timeout: 3

  SubscribeRemoveFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: subscribe/
      Handler: app.handler
      Runtime: nodejs14.x
      Description: A Lambda function that receive Deletion events from the table.
      MemorySize: 128
      Timeout: 3

  #EventBridge specification
  MyEventBus:
    Type: AWS::Events::EventBus
    Properties:
      Name: MyEventBus
  
  #EventBridge rules and permissions
  EventRuleInsert: 
    Type: AWS::Events::Rule
    Properties: 
      Description: "Insert transactions"
      EventBusName: !GetAtt MyEventBus.Arn
      EventPattern: 
        source: 
          - "MyDynamoStream"
        detail-type:
          - transaction   
        detail: 
          eventName: 
            - "INSERT"
      State: "ENABLED"
      Targets: 
        - 
          Arn: !GetAtt SubscribeInsertFunction.Arn
          Id: "eventRuleInsert"
  PermissionForInsertEventsToInvokeLambda: 
    Type: AWS::Lambda::Permission
    Properties: 
      FunctionName: !Ref SubscribeInsertFunction
      Action: "lambda:InvokeFunction"
      Principal: "events.amazonaws.com"
      SourceArn: !GetAtt EventRuleInsert.Arn

  EventRuleRemove: 
    Type: AWS::Events::Rule
    Properties: 
      Description: "Remove transactions"
      EventBusName: !GetAtt MyEventBus.Arn
      EventPattern: 
        source: 
          - "MyDynamoStream"
        detail-type:
          - transaction   
        detail: 
          eventName: 
            - "REMOVE"
      State: "ENABLED"
      Targets: 
        - 
          Arn: !GetAtt SubscribeRemoveFunction.Arn
          Id: "eventRuleRemove"
  PermissionForRemoveEventsToInvokeLambda: 
    Type: AWS::Lambda::Permission
    Properties: 
      FunctionName: !Ref SubscribeRemoveFunction
      Action: "lambda:InvokeFunction"
      Principal: "events.amazonaws.com"
      SourceArn: !GetAtt EventRuleRemove.Arn