ResultType.ts

type Ok<TOk> = {
    kind: 'ok';
    value: TOk | null;
};

type Err<TErr> = {
    kind: 'err';
    value: TErr | null;
    errorMessage: string;
    exception: Error | null;
    code: number | null;
};

export type Result<TOk, TErr = unknown> = Ok<TOk> | Err<TErr>;

export function ok<TOk>(value: TOk | null = null): Ok<TOk> {
    return { kind: 'ok', value };
}

export const success = ok;  // Alias

export function fail<TErr = unknown>(
    errorMessage: string,
    codeOrValue?: number | TErr | null,
    valueOrException?: TErr | Error | null
): Err<TErr> {
    let code: number | null = null;
    let value: TErr | null = null;
    let exception: Error | null = null;

    if (codeOrValue !== undefined) {
        if (typeof codeOrValue === 'number') {
            code = codeOrValue;
            if (valueOrException !== undefined) {
                if (valueOrException instanceof Error) {
                    exception = valueOrException;
                } else {
                    value = valueOrException as TErr;
                }
            }
        } else {
            value = codeOrValue as TErr;
            if (valueOrException !== undefined) {
                if (valueOrException instanceof Error) {
                    exception = valueOrException;
                } else {
                    throw new Error('When second parameter is a value, third parameter must be an Error or null');
                }
            }
        }
    }

    return { kind: 'err', value, errorMessage, exception, code };
}