Union Types

let id: string | number = true;
// Помилка: тип boolean не входить до string | number

function printValue(value: string | number): void {
  console.log(value.toString());

  // value.toUpperCase();
  // Помилка: метод toUpperCase існує у string, але не у number
}

function formatValue(value: string | number): string {
  if (typeof value === "string") {
    return value.toUpperCase();
  }

  return value.toFixed(2);
}

console.log(formatValue("typescript")); // TYPESCRIPT
console.log(formatValue(12.5));         // 12.50

function describe(value: string | number | boolean): string {
  if (typeof value === "string") {
    return `Рядок із довжиною ${value.length}`;
  }

  if (typeof value === "number") {
    return `Число ${value}`;
  }

  return value ? "true" : "false";
}

console.log(describe("hello"));
console.log(describe(100));
console.log(describe(false));

type Direction = "up" | "down" | "left" | "right";

function move(direction: Direction): string {
  if (direction === "up") {
    return "Рух угору";
  }

  if (direction === "down") {
    return "Рух униз";
  }

  if (direction === "left") {
    return "Рух ліворуч";
  }

  return "Рух праворуч";
}

console.log(move("left"));

type Theme = "light" | "dark";

function setTheme(theme: Theme): void {
  console.log(`Встановлено тему: ${theme}`);
}

setTheme("dark");

// setTheme("blue");
// Помилка: "blue" не входить до Theme

type EmailNotification = {
  email: string;
  subject: string;
};

type SmsNotification = {
  phone: string;
  message: string;
};

function sendNotification(
  notification: EmailNotification | SmsNotification
): string {
  if ("email" in notification) {
    return `Email для ${notification.email}: ${notification.subject}`;
  }

  return `SMS на ${notification.phone}: ${notification.message}`;
}

console.log(
  sendNotification({
    email: "user@example.com",
    subject: "Ваше замовлення готове",
  })
);

console.log(
  sendNotification({
    phone: "+380501112233",
    message: "Код підтвердження: 1234",
  })
);

type LoadingState = {
  status: "loading";
};

type SuccessState = {
  status: "success";
  data: string[];
};

type ErrorState = {
  status: "error";
  error: string;
};

type RequestState = LoadingState | SuccessState | ErrorState;

function renderState(state: RequestState): string {
  switch (state.status) {
    case "loading":
      return "Завантаження...";

    case "success":
      return `Отримано елементів: ${state.data.length}`;

    case "error":
      return `Помилка: ${state.error}`;
  }
}

console.log(renderState({ status: "loading" }));

console.log(
  renderState({
    status: "success",
    data: ["TypeScript", "JavaScript"],
  })
);

console.log(
  renderState({
    status: "error",
    error: "Сервер недоступний",
  })
);

type User = {
  id: number;
  name: string;
};

function isUser(value: unknown): value is User {
  if (typeof value !== "object" || value === null) {
    return false;
  }

  if (!("id" in value) || !("name" in value)) {
    return false;
  }

  return typeof value.id === "number" && typeof value.name === "string";
}

function getUserName(value: unknown): string {
  if (isUser(value)) {
    return value.name;
  }

  return "Невідомий користувач";
}

console.log(getUserName({ id: 1, name: "Олена" }));
console.log(getUserName({ id: "1", name: "Олена" }));

type PaymentMethod =
  | { kind: "card"; last4: string }
  | { kind: "cash" }
  | { kind: "bank-transfer"; iban: string };

function assertNever(value: never): never {
  throw new Error(`Непідтримуваний варіант: ${JSON.stringify(value)}`);
}

function describePayment(payment: PaymentMethod): string {
  switch (payment.kind) {
    case "card":
      return `Картка **** ${payment.last4}`;

    case "cash":
      return "Готівка";

    case "bank-transfer":
      return `Банківський переказ: ${payment.iban}`;

    default:
      return assertNever(payment);
  }
}

console.log(
  describePayment({
    kind: "card",
    last4: "1234",
  })
);

const values: Array<string | number> = [
  "TypeScript",
  2026,
  "JavaScript",
  42,
];

for (const value of values) {
  if (typeof value === "string") {
    console.log(value.toUpperCase());
  } else {
    console.log(value.toFixed(0));
  }
}

type Result = string | null;

function findUserName(id: number): Result {
  if (id === 1) {
    return "Олена";
  }

  return null;
}

const name = findUserName(1);

if (name !== null) {
  console.log(name.toUpperCase());
} else {
  console.log("Користувача не знайдено");
}

type Id = string | number;

type HasId = {
  id: number;
};

type HasTimestamp = {
  createdAt: Date;
};

type Entity = HasId & HasTimestamp;

const entity: Entity = {
  id: 1,
  createdAt: new Date(),
};

type Circle = {
  kind: "circle";
  radius: number;
};

type Square = {
  kind: "square";
  side: number;
};

function getArea(shape: Circle | Square): number {
  if (shape.kind === "circle") {
    return Math.PI * shape.radius ** 2;
  }

  return shape.side ** 2;
}

function printLength(value: string | number): void {
  if (typeof value === "string") {
    console.log(value.length);
  }
}

function unsafePrintLength(value: string | number): void {
  console.log((value as string).length);
}

let status: string = "success";

let status: "loading" | "success" | "error" = "loading";