create CDK L2 resource depends on parameter demo

cdk-resource-dependson-parameter-demo.ts

import { App, Construct, Stack, StackProps, CfnParameter, CfnCondition, Fn } from '@aws-cdk/core';
import * as sns from '@aws-cdk/aws-sns';

export interface DemoProps { }

export class Demo extends Construct {
  constructor(scope: Construct, id: string) {
    super(scope, id)

    const stack = Stack.of(this);
    const topic = new sns.Topic(this, 'Topic');
    const input = new CfnParameter(stack, 'YourName', { allowedValues: ['foo', 'bar'] })
    const isFoo = new CfnCondition(stack, 'ISFOO', {
      expression: Fn.conditionEquals(input.valueAsString, 'foo')
    })
    const cfnTopic = topic.node.tryFindChild('Resource') as sns.CfnTopic;
    cfnTopic.cfnOptions.condition = isFoo
  }
}

export class MyStack extends Stack {
  constructor(scope: Construct, id: string, props: StackProps = {}) {
    super(scope, id, props);
    
    new Demo(this, 'Demo');
  }
}

// for development, use account/region from cdk cli
const devEnv = {
  account: process.env.CDK_DEFAULT_ACCOUNT,
  region: process.env.CDK_DEFAULT_REGION,
};

const app = new App();

const stack = new MyStack(app, 'my-stack-dev', { env: devEnv });
// new MyStack(app, 'my-stack-prod', { env: prodEnv });

app.synth();