import 'dart:math';

import 'package:aves/utils/math_utils.dart';
import 'package:latlong2/latlong.dart';

class ScaleBarUtils {
  static LatLng calculateEndingGlobalCoordinates(LatLng start, double startBearing, double distance) {
    var mSemiMajorAxis = 6378137.0; //WGS84 major axis
    var mSemiMinorAxis = (1.0 - 1.0 / 298.257223563) * 6378137.0;
    var mFlattening = 1.0 / 298.257223563;
    // double mInverseFlattening = 298.257223563;

    var a = mSemiMajorAxis;
    var b = mSemiMinorAxis;
    var aSquared = a * a;
    var bSquared = b * b;
    var f = mFlattening;
    var phi1 = toRadians(start.latitude);
    var alpha1 = toRadians(startBearing);
    var cosAlpha1 = cos(alpha1);
    var sinAlpha1 = sin(alpha1);
    var s = distance;
    var tanU1 = (1.0 - f) * tan(phi1);
    var cosU1 = 1.0 / sqrt(1.0 + tanU1 * tanU1);
    var sinU1 = tanU1 * cosU1;

    // eq. 1
    var sigma1 = atan2(tanU1, cosAlpha1);

    // eq. 2
    var sinAlpha = cosU1 * sinAlpha1;

    var sin2Alpha = sinAlpha * sinAlpha;
    var cos2Alpha = 1 - sin2Alpha;
    var uSquared = cos2Alpha * (aSquared - bSquared) / bSquared;

    // eq. 3
    var A = 1 + (uSquared / 16384) * (4096 + uSquared * (-768 + uSquared * (320 - 175 * uSquared)));

    // eq. 4
    var B = (uSquared / 1024) * (256 + uSquared * (-128 + uSquared * (74 - 47 * uSquared)));

    // iterate until there is a negligible change in sigma
    double deltaSigma;
    var sOverbA = s / (b * A);
    var sigma = sOverbA;
    double sinSigma;
    var prevSigma = sOverbA;
    double sigmaM2;
    double cosSigmaM2;
    double cos2SigmaM2;

    for (;;) {
      // eq. 5
      sigmaM2 = 2.0 * sigma1 + sigma;
      cosSigmaM2 = cos(sigmaM2);
      cos2SigmaM2 = cosSigmaM2 * cosSigmaM2;
      sinSigma = sin(sigma);
      var cosSignma = cos(sigma);

      // eq. 6
      deltaSigma = B * sinSigma * (cosSigmaM2 + (B / 4.0) * (cosSignma * (-1 + 2 * cos2SigmaM2) - (B / 6.0) * cosSigmaM2 * (-3 + 4 * sinSigma * sinSigma) * (-3 + 4 * cos2SigmaM2)));

      // eq. 7
      sigma = sOverbA + deltaSigma;

      // break after converging to tolerance
      if ((sigma - prevSigma).abs() < 0.0000000000001) break;

      prevSigma = sigma;
    }

    sigmaM2 = 2.0 * sigma1 + sigma;
    cosSigmaM2 = cos(sigmaM2);
    cos2SigmaM2 = cosSigmaM2 * cosSigmaM2;

    var cosSigma = cos(sigma);
    sinSigma = sin(sigma);

    // eq. 8
    var phi2 = atan2(sinU1 * cosSigma + cosU1 * sinSigma * cosAlpha1, (1.0 - f) * sqrt(sin2Alpha + pow(sinU1 * sinSigma - cosU1 * cosSigma * cosAlpha1, 2.0)));

    // eq. 9
    // This fixes the pole crossing defect spotted by Matt Feemster. When a
    // path passes a pole and essentially crosses a line of latitude twice -
    // once in each direction - the longitude calculation got messed up.
    // Using
    // atan2 instead of atan fixes the defect. The change is in the next 3
    // lines.
    // double tanLambda = sinSigma * sinAlpha1 / (cosU1 * cosSigma - sinU1 *
    // sinSigma * cosAlpha1);
    // double lambda = Math.atan(tanLambda);
    var lambda = atan2(sinSigma * sinAlpha1, (cosU1 * cosSigma - sinU1 * sinSigma * cosAlpha1));

    // eq. 10
    var C = (f / 16) * cos2Alpha * (4 + f * (4 - 3 * cos2Alpha));

    // eq. 11
    var L = lambda - (1 - C) * f * sinAlpha * (sigma + C * sinSigma * (cosSigmaM2 + C * cosSigma * (-1 + 2 * cos2SigmaM2)));

    // eq. 12
    // double alpha2 = Math.atan2(sinAlpha, -sinU1 * sinSigma + cosU1 *
    // cosSigma * cosAlpha1);

    // build result
    var latitude = toDegrees(phi2);
    var longitude = start.longitude + toDegrees(L);

    // if ((endBearing != null) && (endBearing.length > 0)) {
    // endBearing[0] = toDegrees(alpha2);
    // }

    latitude = latitude < -90 ? -90 : latitude;
    latitude = latitude > 90 ? 90 : latitude;
    longitude = longitude < -180 ? -180 : longitude;
    longitude = longitude > 180 ? 180 : longitude;
    return LatLng(latitude, longitude);
  }
}