source: node_modules/d3-geo/src/rotation.js@ e4c61dd

import compose from "./compose.js";
import {abs, asin, atan2, cos, degrees, pi, radians, sin, tau} from "./math.js";

function rotationIdentity(lambda, phi) {
  if (abs(lambda) > pi) lambda -= Math.round(lambda / tau) * tau;
  return [lambda, phi];
}

rotationIdentity.invert = rotationIdentity;

export function rotateRadians(deltaLambda, deltaPhi, deltaGamma) {
  return (deltaLambda %= tau) ? (deltaPhi || deltaGamma ? compose(rotationLambda(deltaLambda), rotationPhiGamma(deltaPhi, deltaGamma))
    : rotationLambda(deltaLambda))
    : (deltaPhi || deltaGamma ? rotationPhiGamma(deltaPhi, deltaGamma)
    : rotationIdentity);
}

function forwardRotationLambda(deltaLambda) {
  return function(lambda, phi) {
    lambda += deltaLambda;
    if (abs(lambda) > pi) lambda -= Math.round(lambda / tau) * tau;
    return [lambda, phi];
  };
}

function rotationLambda(deltaLambda) {
  var rotation = forwardRotationLambda(deltaLambda);
  rotation.invert = forwardRotationLambda(-deltaLambda);
  return rotation;
}

function rotationPhiGamma(deltaPhi, deltaGamma) {
  var cosDeltaPhi = cos(deltaPhi),
      sinDeltaPhi = sin(deltaPhi),
      cosDeltaGamma = cos(deltaGamma),
      sinDeltaGamma = sin(deltaGamma);

  function rotation(lambda, phi) {
    var cosPhi = cos(phi),
        x = cos(lambda) * cosPhi,
        y = sin(lambda) * cosPhi,
        z = sin(phi),
        k = z * cosDeltaPhi + x * sinDeltaPhi;
    return [
      atan2(y * cosDeltaGamma - k * sinDeltaGamma, x * cosDeltaPhi - z * sinDeltaPhi),
      asin(k * cosDeltaGamma + y * sinDeltaGamma)
    ];
  }

  rotation.invert = function(lambda, phi) {
    var cosPhi = cos(phi),
        x = cos(lambda) * cosPhi,
        y = sin(lambda) * cosPhi,
        z = sin(phi),
        k = z * cosDeltaGamma - y * sinDeltaGamma;
    return [
      atan2(y * cosDeltaGamma + z * sinDeltaGamma, x * cosDeltaPhi + k * sinDeltaPhi),
      asin(k * cosDeltaPhi - x * sinDeltaPhi)
    ];
  };

  return rotation;
}

export default function(rotate) {
  rotate = rotateRadians(rotate[0] * radians, rotate[1] * radians, rotate.length > 2 ? rotate[2] * radians : 0);

  function forward(coordinates) {
    coordinates = rotate(coordinates[0] * radians, coordinates[1] * radians);
    return coordinates[0] *= degrees, coordinates[1] *= degrees, coordinates;
  }

  forward.invert = function(coordinates) {
    coordinates = rotate.invert(coordinates[0] * radians, coordinates[1] * radians);
    return coordinates[0] *= degrees, coordinates[1] *= degrees, coordinates;
  };

  return forward;
}