day23.ts

declare const argKey: unique symbol
type ArgKey = typeof argKey

interface Fn {
	[argKey]: unknown
	return: unknown
}

type Apply<TFn extends Fn, TArg> = (TFn & {
	[argKey]: TArg
})['return']

interface Cap extends Fn {
	return: Capitalize<this[ArgKey] & string>
}

interface Push extends Fn {
	return: PushFunc<this[ArgKey]>
}
interface PushFunc<T> extends Fn {
	return: this[ArgKey] extends unknown[] ? [...this[ArgKey], T] : never
}

interface ApplyAll extends Fn {
	return: this[ArgKey] extends Fn ? ApplyAllFunc<this[ArgKey]> : never
}
interface ApplyAllFunc<TFn extends Fn, U extends unknown[] = []> extends Fn {
	impl: U extends [infer F, ...infer R]
		? [Apply<TFn, F>, ...ApplyAllFunc<TFn, R>['impl']]
		: []
	return: this[ArgKey] extends unknown[]
		? ApplyAllFunc<TFn, this[ArgKey]>['impl']
		: never
}

interface Extends extends Fn {
	return: ExtendsFunc<this[ArgKey]>
}
interface ExtendsFunc<T> extends Fn {
	return: this[ArgKey] extends T ? true : false
}

interface Filter extends Fn {
	return: this[ArgKey] extends Fn ? FilterFunc<this[ArgKey]> : never
}
interface FilterFunc<TFn extends Fn, U extends unknown[] = []> extends Fn {
	impl: U extends [infer F, ...infer R]
		? Apply<TFn, F> extends true
			? [F, ...FilterFunc<TFn, R>['impl']]
			: FilterFunc<TFn, R>['impl']
		: []
	return: this[ArgKey] extends unknown[]
		? FilterFunc<TFn, this[ArgKey]>['impl']
		: never
}