How to use the @aws-cdk/aws-kms.Alias function in @aws-cdk/aws-kms

import * as kms from '@aws-cdk/aws-kms';
import * as s3 from '@aws-cdk/aws-s3';
import * as cdk from '@aws-cdk/core';

const REQUIRED_ALIAS_PREFIX = 'alias/';

/**
 * A class needed to work around CodePipeline's extremely small (100 characters)
 * limit for the name/ARN of the key in the ArtifactStore.
 * Limits the length of the alias' auto-generated name to 50 characters.
 */
class AliasWithShorterGeneratedName extends kms.Alias {
  protected generatePhysicalName(): string {
    let baseName = super.generatePhysicalName();
    if (baseName.startsWith(REQUIRED_ALIAS_PREFIX)) {
      // remove the prefix, because we're taking the last characters of the name below
      baseName = baseName.substring(REQUIRED_ALIAS_PREFIX.length);
    }
    const maxLength = 50 - REQUIRED_ALIAS_PREFIX.length;
    // take the last characters, as they include the hash,
    // and so have a higher chance of not colliding
    return REQUIRED_ALIAS_PREFIX + lastNCharacters(baseName, maxLength);
  }
}

function lastNCharacters(str: string, n: number) {
  const startIndex = Math.max(str.length - n, 0);
  return str.substring(startIndex);