type OptionalKeys<T extends Record<string, unknown>> = {
	[K in keyof T]: T extends Record<K, T[K]> ? never : K
}[keyof T]

type RequiredKeys<T extends Record<string, unknown>> = Exclude<
	keyof T,
	OptionalKeys<T>
>

type MonoArgEmitter<T, Keys extends keyof T> = <K extends Keys>(
	evt: K,
	arg?: T[K],
) => void

type BiArgEmitter<T, Keys extends keyof T> = <K extends Keys>(
	evt: K,
	arg: T[K],
) => void

export type EventEmitter<T extends Record<string, unknown>> = MonoArgEmitter<
	T,
	OptionalKeys<T>
> &
	BiArgEmitter<T, RequiredKeys<T>>

export type AnyFunction<T> = (...args: any[]) => T

export type PartialReturnType<
	T extends (...args: unknown[]) => unknown
> = Partial<ReturnType<T>>