// Converts UTM coordinates to latitude and longitude

const a = 6378137.0; // WGS84 Major axis
const eccSquared = 0.00669438; // WGS84 eccentricity squared
const k0 = 0.9996; // Scale factor

function UTMtoLatLon(UTMEasting, UTMNorthing, UTMZoneNumber, Hemisphere) {
    const e1 = (1 - Math.sqrt(1 - eccSquared)) / (1 + Math.sqrt(1 - eccSquared));
    let x = UTMEasting - 500000.0;
    let y = UTMNorthing;

    if (Hemisphere === 'S') {
        y -= 10000000.0;
    }

    const LongOrigin = (UTMZoneNumber - 1) * 6 - 180 + 3;
    const eccPrimeSquared = eccSquared / (1 - eccSquared);
    const M = y / k0;
    const mu = M / (a * (1 - eccSquared / 4 - (3 * eccSquared ** 2) / 64 - (5 * eccSquared ** 3) / 256));

    let phi1Rad = mu + ((3 * e1) / 2 - (27 * e1 ** 3) / 32) * Math.sin(2 * mu) + ((21 * e1 ** 2) / 16 - (55 * e1 ** 4) / 32) * Math.sin(4 * mu) + ((151 * e1 ** 3) / 96) * Math.sin(6 * mu);

    const N1 = a / Math.sqrt(1 - eccSquared * Math.sin(phi1Rad) ** 2);
    const T1 = Math.tan(phi1Rad) ** 2;
    const C1 = eccPrimeSquared * Math.cos(phi1Rad) ** 2;
    const R1 = (a * (1 - eccSquared)) / Math.pow(1 - eccSquared * Math.sin(phi1Rad) ** 2, 1.5);
    const D = x / (N1 * k0);

    let lat = phi1Rad - ((N1 * Math.tan(phi1Rad)) / R1) * (D ** 2 / 2 - ((5 + 3 * T1 + 10 * C1 - 4 * C1 ** 2 - 9 * eccPrimeSquared) * D ** 4) / 24 + ((61 + 90 * T1 + 298 * C1 + 45 * T1 ** 2 - 252 * eccPrimeSquared - 3 * C1 ** 2) * D ** 6) / 720);
    lat *= 180 / Math.PI;

    let lon = (D - ((1 + 2 * T1 + C1) * D ** 3) / 6 + ((5 - 2 * C1 + 28 * T1 - 3 * C1 ** 2 + 8 * eccPrimeSquared + 24 * T1 ** 2) * D ** 5) / 120) / Math.cos(phi1Rad);
    lon = LongOrigin + (lon * 180) / Math.PI;

    return { latitude: lat, longitude: lon };
}

// Converts latitude and longitude to UTM coordinates
function LatLontoUTM(lat, lon) {
    const LatRad = (lat * Math.PI) / 180.0;
    const LongRad = (lon * Math.PI) / 180.0;

    const ZoneNumber = Math.floor((lon + 180) / 6) + 1;
    const LongOrigin = (ZoneNumber - 1) * 6 - 180 + 3;
    const LongOriginRad = (LongOrigin * Math.PI) / 180.0;

    const eccPrimeSquared = eccSquared / (1 - eccSquared);
    const N = a / Math.sqrt(1 - eccSquared * Math.sin(LatRad) ** 2);
    const T = Math.tan(LatRad) ** 2;
    const C = eccPrimeSquared * Math.cos(LatRad) ** 2;
    const A = Math.cos(LatRad) * (LongRad - LongOriginRad);

    const M =
        a *
        ((1 - eccSquared / 4 - (3 * eccSquared ** 2) / 64 - (5 * eccSquared ** 3) / 256) * LatRad -
            ((3 * eccSquared) / 8 + (3 * eccSquared ** 2) / 32 + (45 * eccSquared ** 3) / 1024) * Math.sin(2 * LatRad) +
            ((15 * eccSquared ** 2) / 256 + (45 * eccSquared ** 3) / 1024) * Math.sin(4 * LatRad) -
            ((35 * eccSquared ** 3) / 3072) * Math.sin(6 * LatRad));

    let UTMEasting = k0 * N * (A + ((1 - T + C) * A ** 3) / 6 + ((5 - 18 * T + T ** 2 + 72 * C - 58 * eccPrimeSquared) * A ** 5) / 120) + 500000.0;

    let UTMNorthing = k0 * (M + N * Math.tan(LatRad) * (A ** 2 / 2 + ((5 - T + 9 * C + 4 * C ** 2) * A ** 4) / 24 + ((61 - 58 * T + T ** 2 + 600 * C - 330 * eccPrimeSquared) * A ** 6) / 720));

    const Hemisphere = lat < 0 ? 'S' : 'N';
    if (lat < 0) {
        UTMNorthing += 10000000.0;
    }

    return {
        easting: UTMEasting,
        northing: UTMNorthing,
        zoneNumber: ZoneNumber,
        hemisphere: Hemisphere
    };
}

// Exporting functions as a module
export { UTMtoLatLon, LatLontoUTM };