AdventOfCode-js-2019/12/common.js

const Moon = require("./Moon");
const Vector3 = require("./Vector3");

/**
 * @param {string[]} inputs The day's input
 * @returns {Moon[]} An array of Moon objects
 */
function parseInput(inputs) {
    const moons = [];
    const parseRegex = new RegExp(/x=(-?\d+), y=(-?\d+), z=(-?\d+)/);

    for (const position of inputs) {
        // eslint-disable-next-line no-shadow-restricted-names
        const [undefined, x, y, z] = position.match(parseRegex);
        moons.push(new Moon(new Vector3(parseInt(x, 10), parseInt(y, 10), parseInt(z, 10))));
    }

    return moons;
}

/**
 * Calculate one step of time
 *
 * @param {Moon[]} moons A list of moons
 * @returns {void}
 */
function step(moons) {
    for (let i = 0; i < moons.length - 1; i++) {
        for (let j = i + 1; j < moons.length; j++) {
            // Calculate Moon B's gravity influence on Moon A
            const firstGravity = calculateGravity(moons[i], moons[j]);
            // Invert the signage to represent Moon A's influence on Moon B
            const secondGravity = firstGravity.negate();

            moons[i].velocity.add(firstGravity);
            moons[j].velocity.add(secondGravity);
        }
    }

    moons.forEach((moon) => { moon.position.add(moon.velocity); });
}

/**
 * Find the gravitational influence two moons have on each other
 *
 * @param {Moon} moonA The first moon to consider
 * @param {Moon} moonB The second moon to consider
 *
 * @returns {Vector3} The gravitational influence of Moon B on Moon A
 */
function calculateGravity(moonA, moonB) {
    // The gravitational pull on Moon A caused by Moon B
    const gravityDifference = new Vector3(
        // eslint-disable-next-line no-nested-ternary
        moonB.position.x > moonA.position.x ? 1 : (moonB.position.x < moonA.position.x ? -1 : 0),
        // eslint-disable-next-line no-nested-ternary
        moonB.position.y > moonA.position.y ? 1 : (moonB.position.y < moonA.position.y ? -1 : 0),
        // eslint-disable-next-line no-nested-ternary
        moonB.position.z > moonA.position.z ? 1 : (moonB.position.z < moonA.position.z ? -1 : 0),
    );

    return gravityDifference;
}

module.exports = {
    parseInput,
    step,
};