let Polynomial = require('./polynomial.js');

const to_bytes_ascii = a => a.charCodeAt(0);
const from_bytes_ascii = a => String.fromCharCode(a);
const to_bin = a => {
    var result = "";
    for (var i = 0; i < a.length; i++) {
        var bin = a[i].charCodeAt().toString(2);
        result += Array(8 - bin.length + 1).join("0") + bin;
    }
    return result;
}
const to_ascii = a => {
    a = a.join('');
    return String.fromCharCode(parseInt(a, 2));;
}



const fcs = m => {
    bits = m.map(to_bin); //message in binary
    bits = bits.join('').split('').reverse(); //reverse binary decoded message
    let M = new Polynomial.Class(2, bits);
    let L = new Polynomial.Class(2, new Array(16).fill(1));
    let X = new Polynomial.Class(2, [0, 1]);
    let X16 = Polynomial.power(X, 16);
    let G = new Polynomial.Class(2, [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1]); //jako ze można to od razu wymnożyć

    let fcs = Polynomial.multiply(X16, M);
    fcs = Polynomial.add(fcs,
        Polynomial.multiply(
            Polynomial.power(X, m.length * 8),
            L
        )
    )
    fcs = Polynomial.divide(fcs, G);
    for (let i = 0; i < 16 - fcs.coefficients.length; i++) fcs.coefficients.push(0);
    fcs.coefficients.reverse();
    return fcs.coefficients;
}


function encode(m) {
    m = m.split('');
    let res = fcs(m);

    let f1 = [];
    let f2 = [];
    for (let i = 0; i < res.length; i++) {
        if (i < 8) {
            f1.push(res[i]);
        } else {
            f2.push(res[i]);
        }
    }
    f1 = to_ascii(f1);
    f2 = to_ascii(f2);
    m.push(f1);
    m.push(f2);
    return m;

}

exports.encode = encode;