AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  SAM App for starting ECS game server Tasks on a schedule when needed and a backend API to request game sessions

# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
  Function:
    Timeout: 300

Parameters:
  ECSResourcesStackName: 
      Type: String
      Default: "fleetiq-ecs-vpc-and-ecs-resources"
      Description: Name of the stack for the ECS resources to import
  TaskResourcesStackName: 
      Type: String
      Default: "fleetiq-game-servers-task-definition"
      Description: Name of the stack for the Task resources to import


Resources:

  # Log group and retention for scaling function
  ScalingFunctionLogGroup:
    Type: AWS::Logs::LogGroup
    DependsOn: [ ScalingFunction ]
    Properties:
      LogGroupName: !Sub /aws/lambda/${ScalingFunction}
      RetentionInDays: 30
  
  # Queue for available active sessions for the backend
  MatchMakingTicketsQueue: 
    Type: AWS::SQS::Queue
    Properties: 
      ReceiveMessageWaitTimeSeconds: 1 #Wait 1 second for messaged to arrive by default

  # API for Frontend functionality
  FrontEndAPI:
    Type: AWS::Serverless::Api
    Properties:
      StageName: Prod
      # Authenticate users with IAM (Cognito identities)
      Auth:
        DefaultAuthorizer: AWS_IAM
        InvokeRole: NONE #Using the Lambda role instead of caller

  # Scheduled Lambda function to start new game server ECS Tasks whenever there's capacity available
  ScalingFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: functions/
      Handler: scaler.lambda_handler
      Runtime: python3.7
      MemorySize: 1024
      ReservedConcurrentExecutions: 1 # We always want exactly one copy of this function running at maximum
      EventInvokeConfig:
        MaximumEventAgeInSeconds: 60 # Don't keep events in queue for long.
        MaximumRetryAttempts: 1 # Sometimes the execution of the previous function can overlap so one retry makes sense
      # Environment variables from other stacks to access the resources
      Environment:
        Variables:
          ECS_CLUSTER_NAME: 
            Fn::ImportValue:
                  !Sub "${ECSResourcesStackName}:ClusterName"
      Policies:
        - AWSCloudFormationReadOnlyAccess
        - AmazonECS_FullAccess
        - CloudWatchReadOnlyAccess
      Events:
        CheckScalingNeeds:
          Type: Schedule
          Properties:
            Schedule: rate(1 minute)

  # Function called by clients through the API to request a game session
  RequestGameSession:
    Type: AWS::Serverless::Function 
    Properties:
      CodeUri: functions/
      Handler: requestgamesession.lambda_handler
      Runtime: python3.7
      MemorySize: 1024
      Timeout: 15
      Policies:
        - AmazonSQSFullAccess
        - Version: 2012-10-17
          Statement:
            - Effect: Allow
              Action: 'gamelift:*'
              Resource: '*'
      # Environment variables from other stacks to access the resources
      Environment:
        Variables:
          SQS_QUEUE_URL: !Ref MatchMakingTicketsQueue
      Events:
        GetGameSession:
          Type: Api
          Properties:
            RestApiId: !Ref FrontEndAPI
            Path: /requestgamesession
            Method: get

Outputs:
  ScalingFunction:
    Description: "Scaling Lambda Function ARN"
    Value: !GetAtt ScalingFunction.Arn
  ScalingFunctionIamRole:
    Description: "Implicit IAM Role created for Scaling function"
    Value: !GetAtt ScalingFunction.Arn
  FrontEndAPI:
    Description: "API Gateway endpoint URL for Prod stage for FrontEndAPI"
    Value: !Sub "https://${FrontEndAPI}.execute-api.${AWS::Region}.amazonaws.com/Prod/"
  FrontEndApiArn:
    Description: "The Execute ARN for the Cognito Role Permissions"
    Value: !Sub "arn:${AWS::Partition}:execute-api:${AWS::Region}:${AWS::AccountId}:${FrontEndAPI}/*/*/*"
    Export:
      Name: !Sub ${AWS::StackName}:FrontEndApiArn