import math from 'mathjs';

// convert degrees (lat/long) to radians
const radians = (deg) => (deg / 360) * 2 * Math.PI;

// create a set of points around the origin at the given radius
const rotatedPointsOrigin = (radius, sides) => {
  const z = new math.complex({ phi: 0, r: radius });
  const angle = (2 * Math.PI) / sides;
  return map(range(sides), (x) => {
    const i = math.complex(0, 1);
    const point = math.multiply(z, math.exp(math.multiply(x, angle, math.complex(0, 1))));
    return [math.re(point), math.im(point)];
  });
};

// scale points to coordinate system
// const latFactor = 69.172 // if miles
const latFactor = 111321.543 // if meters
const scalePoints = (points, lat) => {
  const lngFactor = math.cos(radians(lat)) * latFactor;
  return map(points, (x) => [x[0] / latFactor, x[1] / lngFactor]);
};

// move this circle to the correct place on the map
const translatePoints = (points, center) => map(
  points,
  (point) => [point[0] + center[0], point[1] + center[1]],
);

// create GeoJSON feature from circle
// (using a 24 sided approximation by default)
export const generateCircleApprox = (radius, unit, center, sides = 24) => {
  console.log('stuff', radius, unit, center, sides);
  const points = rotatedPointsOrigin(radius, sides);
  const scaledPoints = scalePoints(points, center[0]);
  const translatedPoints = translatePoints(scaledPoints, center);
  const reversedPoints = map(translatedPoints, (x) => reverse(x));
  return {
    type: 'Feature',
    properties: {
      radius,
      unit,
      center,
      sides,
    },
    geometry: {
      type: 'MultiPolygon',
      coordinates: [[reversedPoints]],
    },
  };
};