class-match.ts

// library
type Handler<T, R> = [new (...args: any) => T, (input: T) => R];

type HandlerPattern<T extends Handler<any, any>> = T extends Handler<
  infer Pattern,
  any
>
  ? Pattern
  : unknown;

type HandlerOutput<T extends Handler<any, any>> = T extends Handler<
  any,
  infer Output
>
  ? Output
  : unknown;

type Handlers<T> = Handler<any, T>[];

type HandlersOutput<T extends Handlers<any>> = T extends Handlers<infer R>
  ? R
  : unknown;

type UniquePattern<T, HS extends Handlers<any>> = T extends HandlerPattern<
  HS[number]
>
  ? never
  : T;

class Match<T extends Handlers<any>> {
  input: unknown;
  patterns: T;
  constructor(input: unknown, patterns: T) {
    this.input = input;
    this.patterns = patterns;
  }
  case<U, R extends HandlersOutput<T>>(
    Ctor: new (...args: any) => UniquePattern<U, T>,
    handler: (data: U) => R
  ): Match<[...T, Handler<U, R>]> {
    return new Match(this.input, [...this.patterns, [Ctor, handler]]);
  }
  default<R extends HandlersOutput<T>>(
    handler: (input: unknown) => R
  ): HandlersOutput<T> {
    for (const [Ctor, handler] of this.patterns) {
      if (this.input instanceof Ctor) {
        return handler(this.input);
      }
    }
    return handler(this.input);
  }
}

const match = (input: unknown): Match<[]> => {
  return new Match(input, []);
};

// email example
abstract class BaseEmail {
  value: string;
  constructor(email: string) {
    this.value = email;
  }
  getEmail() {
    return this.value;
  }
}

class ValidEmail extends BaseEmail {
  getValidEmail() {
    return this.getEmail();
  }
}

class InvalidEmail extends BaseEmail {
  getInvalidEmail() {
    return this.getEmail();
  }
}

class AnotherEmail extends BaseEmail {
  getAnotherEmail() {
    return this.getEmail();
  }
}

const createEmail = (inputEmail: string): BaseEmail => {
  if (inputEmail.includes('@')) {
    return new ValidEmail(inputEmail);
  }
  return new InvalidEmail(inputEmail);
};

const handleValidEmail = (email: ValidEmail) => {
  return `valid email ${email.getValidEmail()}`;
};

const handleInvalidEmail = (email: InvalidEmail) => {
  return `invalid email ${email.getInvalidEmail()}`;
};

const email0 = createEmail('abc');
const email1 = createEmail('abc@example');
const email2 = new AnotherEmail('another@example');

const result0 = match(email0)
  .case(ValidEmail, handleValidEmail)
  .case(InvalidEmail, handleInvalidEmail)
  .default(() => 'default 0');

const result1 = match(email1)
  .case(ValidEmail, handleValidEmail)
  .case(InvalidEmail, handleInvalidEmail)
  .default(() => 'default 1');

const result2 = match(email2)
  .case(ValidEmail, handleValidEmail)
  .case(InvalidEmail, handleInvalidEmail)
  .default(() => 'default 2');

console.log({
  result0,
  result1,
  result2,
});