type-fest/source/conditional-pick-deep.d.ts

A collection of essential TypeScript types

import type {Opaque} from './opaque';
import type {IsEqual} from './is-equal';
import type {ConditionalExcept} from './conditional-except';
import type {ConditionalSimplifyDeep} from './conditional-simplify';

/**
Used to mark properties that should be excluded.
*/
type ConditionalPickDeepSymbol = Opaque<symbol, 'conditional-pick-deep-symbol'>;

/**
Assert the condition according to the {@link ConditionalPickDeepOptions.condition|condition} option.
*/
type AssertCondition<Type, Condition, Options extends ConditionalPickDeepOptions> = Options['condition'] extends 'equality'
	? IsEqual<Type, Condition>
	: Type extends Condition
		? true
		: false;

/**
ConditionalPickDeep options.

@see ConditionalPickDeep
*/
export type ConditionalPickDeepOptions = {
	/**
	The condition assertion mode.

	@default 'extends'
	*/
	condition?: 'extends' | 'equality';
};

/**
Pick keys recursively from the shape that matches the given condition.

@see ConditionalPick

@example
```
import type {ConditionalPickDeep} from 'type-fest';

interface Example {
	a: string;
	b: string | boolean;
	c: {
		d: string;
		e: {
			f?: string;
			g?: boolean;
			h: string | boolean;
			i: boolean | bigint;
		};
		j: boolean;
	};
}

type StringPick = ConditionalPickDeep<Example, string>;
//=> {a: string; c: {d: string}}

type StringPickOptional = ConditionalPickDeep<Example, string | undefined>;
//=> {a: string; c: {d: string; e: {f?: string}}}

type StringPickOptionalOnly = ConditionalPickDeep<Example, string | undefined, {condition: 'equality'}>;
//=> {c: {e: {f?: string}}}

type BooleanPick = ConditionalPickDeep<Example, boolean | undefined>;
//=> {c: {e: {g?: boolean}; j: boolean}}

type NumberPick = ConditionalPickDeep<Example, number>;
//=> {}

type StringOrBooleanPick = ConditionalPickDeep<Example, string | boolean>;
//=> {
// 	a: string;
// 	b: string | boolean;
// 	c: {
// 		d: string;
// 		e: {
// 			h: string | boolean
// 		};
// 		j: boolean;
// 	};
// }

type StringOrBooleanPickOnly = ConditionalPickDeep<Example, string | boolean, {condition: 'equality'}>;
//=> {b: string | boolean; c: {e: {h: string | boolean}}}
```

@category Object
*/
export type ConditionalPickDeep<
	Type,
	Condition,
	Options extends ConditionalPickDeepOptions = {},
> = ConditionalSimplifyDeep<ConditionalExcept<{
	[Key in keyof Type]: AssertCondition<Type[Key], Condition, Options> extends true
		? Type[Key]
		: Type[Key] extends object
			? ConditionalPickDeep<Type[Key], Condition, Options>
			: ConditionalPickDeepSymbol;
}, (ConditionalPickDeepSymbol | undefined) | Record<PropertyKey, never>>>;