/**
 * Returns a new object which is a subset of the input, including only the specified properties.
 * Can be called with a single argument (array of props to pick), in which case it returns a partially
 * applied pick function.
 */
export function pick<T extends string>(props: T[]): <U>(input: U) => Pick<U, Extract<keyof U, T>>;
export function pick<U, T extends keyof U>(input: U, props: T[]): { [K in T]: U[K] };
export function pick<U, T extends keyof U>(
    inputOrProps: U | T[],
    maybeProps?: T[],
): { [K in T]: U[K] } | ((input: U) => Pick<U, Extract<keyof U, T>>) {
    if (Array.isArray(inputOrProps)) {
        return (input: U) => _pick(input, inputOrProps);
    } else {
        return _pick(inputOrProps, maybeProps || []);
    }
}

function _pick<U, T extends keyof U>(input: U, props: T[]): { [K in T]: U[K] } {
    const output: any = {};
    for (const prop of props) {
        output[prop] = input[prop];
    }
    return output;
}