aureooms/js-random

/**
 * Builds a randrange function given a randint function.
 *
 * @param {Function} randint The randint function.
 * @return {Function} The choice function.
 */
const _randrange = (randint) => {
    /**
     * Pick an element from range(start, stop, step) uniformly at random.
     *
     * Return an element from range(start, stop, step) selected uniformly at random.
     * If step is positive, this set corresponds to
     * {x: x in [start, stop[ AND x % step = 0}.
     * If step is negative, the range has to be given in reverse order, that is,
     * largest value first, smallest value second. Both the starting value and the
     * step value are optional. By default the starting value is <code>0</code>.
     * The default for the step value is <code>1</code>.
     *
     * TODO: Handle empty ranges.
     *
     * @param {number} [start=0] - The starting value.
     * @param {number} stop - The stopping value.
     * @param {number} [step=1] - The step value.
     * @return {number} The picked element.
     */
    const randrange = (start, stop, step) => {
        if (stop === undefined) return randint(0, start);
        if (step === undefined) step = 1;

        return start + step * randint(0, Math.floor((stop - start) / step));
    };

    return randrange;
};

export default _randrange;