Generate AWS Cognito password

https://www.npmjs.com/package/aws-cognito-temporary-password-generator

/**
 * Configuration of Password generation.
 * Only possible to specify length. default: 16
 * All Other requirements are automatically satisfy
 * Require numbers
 * Require a special character from this set:
 * = + - ^ $ * . [ ] { } ( ) ? " ! @ # % & / \ , > < ' : ; | _ ~ `
 * Require uppercase letters
 * Require lowercase letters
 * 
 * https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-policies.html
 */
interface Config {
  length: number;
}

type PasswordValue = string;

/**
 * Generate Password 
 */
export class CognitoPassword {
  MINIMUM_LENGTH = 6
  DEFAULT_LENGTH = 16
  CHARS = [
    'abcdefghijklmnopqrstuvwwyz',
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
    '0123456890',
    '+-^$*.[]{}()?"!@#%&/\,><\':;|_~'
  ]

  /**
   * Generate password
   * @param config {Config}
   * @returns {PasswordValue}
   */
  public generate(config?: Config): PasswordValue {
    const length = (!config || Object.keys(config).length <= 0 || config.length < this.MINIMUM_LENGTH) ? this.DEFAULT_LENGTH : config.length
    let password: PasswordValue = ''
    let indexHistory: number[] = []
    const gen = () => {
      let p = ''
      for(let i = 0; i < length; i++) {
        const idx = Math.floor(Math.random() * 4)
        indexHistory.push(idx)
  
        const set = this.CHARS[idx]
        const l = set.length
        const idx2 = Math.floor(Math.random() * l)
        const chr = set[idx2]
        p = p += chr
      }
      return p
    }

    password = gen()
    if (indexHistory.includes(0)
      && indexHistory.includes(1)
      && indexHistory.includes(2)
      && indexHistory.includes(3)) {
        return password
    } else {
      indexHistory = []
      return gen()
    }
  }
}

export default CognitoPassword