function foo(obj, max, value) {
    const keys = Object.keys(obj);
    const x = keys.map(key => Math.max(0, max - obj[key]))
                  .reduce((a, b) => a + b, 0);

    const result = {};

    for (const key of keys) {
        result[key] = value / x * Math.max(0, max - obj[key]);
    }

    return result;
}