declare function spected<ROOTINPUT, SPEC extends SpecValue<ROOTINPUT, ROOTINPUT> = SpecValue<ROOTINPUT, ROOTINPUT>>(
    spec: SPEC,
    input: ROOTINPUT,
): Result<ROOTINPUT, SPEC>;

type Predicate<INPUT, ROOTINPUT> = (value: INPUT, inputs: ROOTINPUT) => boolean;

type ErrorMsg<INPUT> =
    | (string | number | boolean | symbol | null | undefined | object)
    | ((value: INPUT, field: string) => any);

export type Spec<INPUT, ROOTINPUT = any> = [Predicate<INPUT, ROOTINPUT>, ErrorMsg<INPUT>];

export type SpecArray<INPUT, ROOTINPUT = any> = Array<Spec<INPUT, ROOTINPUT>>;

export type SpecFunction<INPUT, ROOTINPUT = any> = [INPUT] extends [ReadonlyArray<infer U>]
    ? (value: INPUT) => ReadonlyArray<SpecArray<U, ROOTINPUT>>
    : [INPUT] extends [object] ? (value: INPUT) => SpecObject<INPUT, ROOTINPUT>
    : (value: INPUT) => SpecArray<INPUT, ROOTINPUT>;

export type SpecObject<INPUT, ROOTINPUT = any> = Partial<{ [key in keyof INPUT]: SpecValue<INPUT[key], ROOTINPUT> }>;

export type SpecValue<INPUT, ROOTINPUT = any> = [INPUT] extends [readonly any[]]
    ? SpecArray<INPUT, ROOTINPUT> | SpecFunction<INPUT, ROOTINPUT>
    : [INPUT] extends [object]
        ? SpecArray<INPUT, ROOTINPUT> | SpecFunction<INPUT, ROOTINPUT> | SpecObject<INPUT, ROOTINPUT>
    : SpecArray<INPUT, ROOTINPUT> | SpecFunction<INPUT, ROOTINPUT>;

export type Result<INPUT, SPEC> = { [key in keyof INPUT]: true | any[] | Result<INPUT[key], any> };

export default spected;

Additional Details

Last updated: Mon, 20 Nov 2023 2324 GMT
Dependencies: none

Credits

These definitions were written by Benjamin Makus.