class Polynomial {
    constructor(coefArray) {
        this.degree = coefArray.length - 1;
        this.coefficients = coefArray;
    }
}

exports.Class = Polynomial;

function multiply(p1, p2, n) {

    let f = p1.coefficients;
    let g = p2.coefficients;
    result = new Array(f.length + g.length - 1).fill(0);

    let tmp = [];
    for (let i = 0; i < f.length; i++) {
        for (let j = 0; j < g.length; j++) {
            result[i + j] += f[i] * g[j];
        }
    }
    return new Polynomial(result.map(x => (x % n) + (x < 0 ? n : 0)));
}

function divide(p1, p2, n) {

    let inverse = (x) => {
        for (let i = 1; i < 2; i++) {
            let r = (i * x) % 2;
            if (r == 1)
                return i
            else
                throw "divisionError"

        }
    }
    if (p1.degree < p2.degree)
        return p1;
    let f = p1.coefficients;
    let g = p2.coefficients;
    let g_lead_coef = g[g.length - 1];
    let g_deg = p2.degree;

    while (f.length >= g.length) {

        let f_lead_coef = f[f.length - 1];
        let tmp_coef = f_lead_coef * inverse(g_lead_coef);
        let tmp_exp = f.length - 1 - g_deg;
        let tmp = [];
        for (let i = 0; i < tmp_exp; i++) {
            tmp.push(0);
        }
        tmp.push(tmp_coef);
        tmp_poly = new Polynomial(tmp);
        let sub = multiply(p2, tmp_poly, n);
        let tmp_f = [];
        for (let i = 0; i < f.length; i++) {
            for (let j = 0; j < sub.coefficients.length; j++) {
                if (i == j)
                    tmp_f.push(f[i] - sub.coefficients[j]);
            }
        }

        f = tmp_f.map(x => (x % n) + (x < 0 ? n : 0));
        while (f && f[f.length - 1] === 0)
            f.pop();

    }
    return new Polynomial(f);
}

function gcd(p1, p2, n) {
    if (p2.coefficients.length === 0) {
        return p1;
    }
    return gcd(p2, divide(p1, p2, n), n);
}

exports.multiply = multiply;
exports.divide = divide;
exports.gcd = gcd;