interface StringContainer {
  value: string;
  format(): string;
  split(): string[];
}

interface NumberContainer {
  value: number;
  nearestPrime: number;
  round(): number;
}

type Item1<T> = {
  id: T,
  container: any;
};

const item1: Item1<string> = {
  id: "aaaaaa",
  container: null
};

type Item2<T> = {
  id: T;
  container: T extends string ? StringContainer : NumberContainer;
};

const item2: Item2<string> = {
  id: 'aaaaaa',
  container: null, // Type 'null' is not assignable to type 'StringContainer'.
};

type Item3<T> = {
  id: T extends string | number ? T : never;
  container: T extends string
    ? StringContainer
    : T extends number
    ? NumberContainer
    : never;
};

const item3: Item3<boolean> = {
  id: true, // Type 'boolean' is not assignable to type 'never'.
  container: null, // Type 'null' is not assignable to type 'never'.
};

type ArrayFilter<T> = T extends any[] ? T : never;

type StringsOrNumbers = ArrayFilter<string | number | string[] | number[]>;

// 1. string | number | string[] | number[]
// 2. never | never | string[] | number[]
// 3. string[] | number[]

interface Table {
  id: string;
  chairs: string[];
}

interface Dino {
  id: number;
  legs: number;
}

interface World {
  getItem<T extends string | number>(id: T): T extends string ? Table : Dino;
}

let world: World = null as any;

const dino = world.getItem(10);
const what = world.getItem(true); // Error! Argument of type 'boolean' is not assignable to parameter of type 'string | number'.ts(2345)

type Flatten<T> = T extends any[]
  ? T[number]
  : T extends object
  ? T[keyof T]
  : T;


const numbers = [1, 2, 3];
type NumbersArrayFlattened = Flatten<typeof numbers>;
// 1. number[]
// 2. number

const person = {
  name: 'Mark',
  age: 38
};
                             
type SomeObjectFlattened = Flatten<typeof person>;
// 1. keyof T --> "id" | "name"
// 2. T["id" | "name"] --> T["id"] | T["name"] --> number | string

const isMale = true;
type SomeBooleanFlattened = Flatten<typeof isMale>;
// true

type UnpackPromise<T> = T extends Promise<infer K>[] ? K : any;
const promises = [Promise.resolve('Mark'), Promise.resolve(38)];

type Expected = UnpackPromise<typeof promises>; // string | number

function plus1(seed: number): number {
  return seed + 1;
}

type MyReturnType<T extends (...args: any) => any> = T extends (
  ...args: any
) => infer R
  ? R
  : any;

type Id = MyReturnType<typeof plus1>;

lookupEntity(plus1(10));

function lookupEntity(id: Id) {
  // query DB for entity by ID
}

// type Exclude<T, U> = T extends U ? never : T;
type Excluded = Exclude<string | number, string>; // number - diff

// type Extract<T, U> = T extends U ? T : never;
type Extracted = Extract<string | number, string>; // string - filter

// Pick<T, Exclude<keyof T, K>>; (Mapped Type)
type Picked = Pick<{name: string, age: number}, 'name'>;

// type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
type Omited = Omit<{name: string, age: number}, 'name'>;

// type NonNullable<T> = T extends null | undefined ? never : T;
type NonNullabled = NonNullable<string | number | null | undefined>;

/*
type ReturnType<T extends (...args: any) => any> = T extends (
  ...args: any
) => infer R
  ? R
  : any;
*/

/*
type Parameters<T extends (...args: any) => any> = T extends (
  ...args: infer P
) => any
  ? P
  : never;
*/
type MyParameters = Parameters<(name: string, age: number) => void>; // [name: string, age: number]

type FunctionPropertyNames<T> = {
  [K in keyof T]: T[K] extends Function ? K : never;
}[keyof T];
type FunctionProperties<T> = Pick<T, FunctionPropertyNames<T>>;

type NonFunctionPropertyNames<T> = {
  [K in keyof T]: T[K] extends Function ? never : K;
}[keyof T];
type NonFunctionProperties<T> = Pick<T, NonFunctionPropertyNames<T>>;

interface Person {
  id: number;
  name: string;
  hello(message: string): void;
}

type T1 = FunctionPropertyNames<Person>;
type T2 = NonFunctionPropertyNames<Person>;
type T3 = FunctionProperties<Person>;
type T4 = NonFunctionProperties<Person>;

interface Constructor {
  new (name: string, age: number): string;
}

/*
type ConstructorParameters<
  T extends new (...args: any) => any
> = T extends new (...args: infer P) => any ? P : never;
*/

type MyConstructorParameters = ConstructorParameters<Constructor>; // [name: string, age: number]

/*
type InstanceType<T extends new (...args: any) => any> = T extends new (
  ...args: any
) => infer R
  ? R
  : any;
*/

type MyInstanceType = InstanceType<Constructor>; // string

type DeepReadonly<T> = T extends (infer E)[]
  ? ReadonlyArray<DeepReadonlyObject<E>>
  : T extends object
  ? DeepReadonlyObject<T>
  : T;

type DeepReadonlyObject<T> = { readonly [K in keyof T]: DeepReadonly<T[K]> };

type IDeepReadonlyRootState = DeepReadonly<IRootState>;
let state2: IDeepReadonlyRootState = {} as IDeepReadonlyRootState;
const book2 = state2.book.books[0];
book2.title = 'new'; // error! Cannot assign to 'title' because it is a read-only property.