'use strict';

/**
 * Choose an index at random among a list of weights,
 * more weighted indices have a greater proability to be chosen
 *
 * @param {Array} weights List of weights
 * @return {number} Selected index
 */
const chooseIndex = weights => {
    const number = Math.random();
    let sum = 0, index = 0;

    while (number >= sum) {
        sum += weights[index];
        index += 1;
    }

    return index - 1;
};

/**
 * Apply the chaos game: starting from `start`, we plot
 * the next `n` points. To get to the next point, we apply
 * a random transformation among given ones
 *
 * @param {ImageData} image Image to write on
 * @param {Array} start Starting point
 * @param {number} iterations Number of points to plot
 * @param {Array} transforms List of available transforms
 * @param {Array} weights Probability weights for each transform
 * @return {null}
 */
export const applyChaos = (image, start, iterations, transforms, weights, cb) => {
    let point = start;

    if (weights === undefined) {
        weights = Array.apply(null, Array(transforms.length)).map(
            () => 1 / transforms.length
        );
    }

    while (iterations--) {
        const index = chooseIndex(weights);
        point = transforms[index](point);

        cb(point);
    }
};