// Constrain generic to require properties
function loggingIdentity<T extends { length: number }>(arg: T): T {
  console.log(arg.length);
  return arg;
}

// Type parameter constrained by another
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

// Default type parameter
type Container<T = string> = { value: T };

interface User { id: number; name: string; email: string; }

type PartialUser = Partial<User>;           // All optional
type RequiredUser = Required<PartialUser>;  // All required
type ReadonlyUser = Readonly<User>;         // All readonly
type UserPreview = Pick<User, "id" | "name">;
type UserWithoutEmail = Omit<User, "email">;

// Function types - define the function first
function fetchUser(id: number): Promise<User> { /* ... */ }

type Params = Parameters<typeof fetchUser>;     // [number]
type Return = ReturnType<typeof fetchUser>;     // Promise<User>
type Unwrapped = Awaited<ReturnType<typeof fetchUser>>;  // User

// typeof and instanceof narrowing
function process(value: string | number) {
  if (typeof value === "string") return value.toUpperCase();
  return value.toFixed(2);
}

// User-defined type predicate
function isFish(pet: Fish | Bird): pet is Fish {
  return (pet as Fish).swim !== undefined;
}

// Discriminated unions with exhaustiveness checking
interface Circle { kind: "circle"; radius: number; }
interface Square { kind: "square"; sideLength: number; }
type Shape = Circle | Square;

function getArea(shape: Shape): number {
  switch (shape.kind) {
    case "circle": return Math.PI * shape.radius ** 2;
    case "square": return shape.sideLength ** 2;
    default: const _: never = shape; return _;  // Exhaustiveness
  }
}

// Transform all properties
type OptionsFlags<T> = { [P in keyof T]: boolean };

// Remove modifiers
type Mutable<T> = { -readonly [P in keyof T]: T[P] };
type Concrete<T> = { [P in keyof T]-?: T[P] };

// Key remapping with template literals
type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
};

// Basic conditional
type IsString<T> = T extends string ? true : false;

// Inferring types
type Flatten<T> = T extends Array<infer Item> ? Item : T;
type GetReturnType<T> = T extends (...args: any[]) => infer R ? R : never;

// Distributive behavior (over unions)
type ToArray<T> = T extends any ? T[] : never;
type Result = ToArray<string | number>;  // string[] | number[]

// Prevent distribution (wrap in tuple)
type ToArrayNonDist<T> = [T] extends [unknown] ? T[] : never;
type Result = ToArrayNonDist<string | number>;  // (string | number)[]

if ("a" in obj) { console.log(obj.a); }

// Add missing case or default with never check

console.log(user.address?.city);
if (user.address) { console.log(user.address.city); }

// Use unknown instead of any
function processData(data: unknown): string {
  if (typeof data === "string") return data.toUpperCase();
  throw new Error("Unsupported type");
}
type AnyObject = Record<string, unknown>;
type AnyFunction = (...args: unknown[]) => unknown;

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true
  }
}

// satisfies - validate type without widening
const config = {
  port: 8080,
  host: "localhost"
} satisfies Record<string, string | number>;
// config.port is number, not string | number

// const type parameters (TS 5.0+)
function createArray<const T extends readonly unknown[]>(items: T): T {
  return items;
}
const arr = createArray([1, 2, 3]);  // readonly [1, 2, 3], not number[]

// using declarations (TS 5.2+)
async function processFile() {
  using file = await openFile("data.txt");
  // file automatically disposed at end of scope
}