Equation Parser and Calculator

equation-calculator-challenge.js

const _ = require('lodash');

function getEquationVariables(equation) {
    variables = equation.match(/[a-z]/g);
    return _.chain(variables).compact().uniq().value();
}

function getAllVariables(equations) {
    return _.chain(equations)
    .map(getEquationVariables)
    .flatten()
    .uniq()
    .value();
}

function invertTerm(term) {
    const NEGATIVE_TERM_REGEX = /^-/;
    return term.match(NEGATIVE_TERM_REGEX)
        ? term.replace(NEGATIVE_TERM_REGEX, '')
        : (
            term === '0' ? term : `-${term}`
        );
}

function matchEquationToZero(equation) {
    const parts = splitEquationInTwoParts(isZeroLeft(equation) ? invertZero(equation) : equation);
    const leftTerms = removeMinusSign(parts[0]);
    const rightTerms = removeMinusSign(parts[1]);

    const zeroEq = leftTerms.concat(rightTerms.map(invertTerm));
    
    return zeroEq[zeroEq.length -1].match(/[a-z]/) ? zeroEq.concat('0') : zeroEq;
}

function extractCoeficient(part) {
    const coeficient = part.match(/(-?[\d\.]*)/);

    if(!coeficient || !coeficient[0]) return 1;
    if(coeficient[0] === '-') return -1;
    return parseFloat(coeficient[0], 10);
}

function extractCoeficients(parts) {
    return parts.map(extractCoeficient);
}

function removeMinusSign(part) {
    const terms = part.split(' ');
    return terms.map((term, i) => isMinus(term)
        ? '+'
        : (
            isMinus(terms[i - 1])
            ? invertTerm(term)
            : term
        )
    ).filter(term => term !== '+');
}

const isMinus = term => term === '-';

function isEquationEqualsZero(equation) {
    const parts = splitEquationInTwoParts(equation);
    return parts[0] === '0' || parts[1] === '0';
}
function isZeroLeft(equation) {
    const parts = splitEquationInTwoParts(equation);
    return parts[0] === '0';
}
function invertZero(equation) {
    const parts = splitEquationInTwoParts(equation);
    return `${parts[1]} = ${parts[0]}`;
}

function convertEquationToCoeficients(equation) {
    const eq = simplifyEquation(equation);
    const terms = matchEquationToZero(eq);
    return extractCoeficients(terms);
}

const splitEquationInTwoParts = equation => equation.replace(/ ?= ?/, '=').split('=');

function simplifyEquation(equation) {
    return equation.toLowerCase()
        .replace(/\+/g, ' + ')
        .replace(/-/g, ' - ')
        .replace(/=/g, ' = ')
        .replace(/ +/g, ' ') // trailing spaces
        .replace(/^ /g, '')  // space in beggining
        .replace(/ $/g, '') // space in end
        .replace(/^\+ /, '') // remove + from beggining
}

module.exports = {
    getEquationVariables,
    getAllVariables,
    simplifyEquation,
    invertTerm,
    isEquationEqualsZero,
    matchEquationToZero,
    removeMinusSign,
    extractCoeficient,
    extractCoeficients,
    convertEquationToCoeficients,
}