AdventOfCode-js-2019/12/12_1.js

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

const input = parseInput([
    "<x=14, y=15, z=-2>",
    "<x=17, y=-3, z=4>",
    "<x=6, y=12, z=-13>",
    "<x=-2, y=10, z=-8>",
]);

const tests = parseInput([
    "<x=-1, y=0, z=2>",
    "<x=2, y=-10, z=-7>",
    "<x=4, y=-8, z=8>",
    "<x=3, y=5, z=-1>",
]);

const STEPS = 1000;

for (let i = 0; i < STEPS; i++) {
    step(input);
}

console.log(`Total energy in system is: ${calculateTotalEnergy(input)}`);

/**
 * 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;
}

/**
 * Calculate the total energy in the system
 *
 * The total energy in the system is the sum of the sum of the positional
 * values multiplied by the sum of the velocity values.
 *
 * @param {Moon[]} moons The moons in the system
 * @returns {number} The total energy in the system
 */
function calculateTotalEnergy(moons) {
    let energy = 0;

    for (const moon of moons) {
        const potentialEnergy = Math.abs(moon.position.x) + Math.abs(moon.position.y) + Math.abs(moon.position.z);
        const kineticEnergy = Math.abs(moon.velocity.x) + Math.abs(moon.velocity.y) + Math.abs(moon.velocity.z);
        energy += potentialEnergy * kineticEnergy;
    }

    return energy;
}

/**
 * @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;
}

// console.log(util.inspect(parseInput(input)));