source: node_modules/d3-geo/src/bounds.js@ a762898

import {Adder} from "d3-array";
import {areaStream, areaRingSum} from "./area.js";
import {cartesian, cartesianCross, cartesianNormalizeInPlace, spherical} from "./cartesian.js";
import {abs, degrees, epsilon, radians} from "./math.js";
import stream from "./stream.js";

var lambda0, phi0, lambda1, phi1, // bounds
    lambda2, // previous lambda-coordinate
    lambda00, phi00, // first point
    p0, // previous 3D point
    deltaSum,
    ranges,
    range;

var boundsStream = {
  point: boundsPoint,
  lineStart: boundsLineStart,
  lineEnd: boundsLineEnd,
  polygonStart: function() {
    boundsStream.point = boundsRingPoint;
    boundsStream.lineStart = boundsRingStart;
    boundsStream.lineEnd = boundsRingEnd;
    deltaSum = new Adder();
    areaStream.polygonStart();
  },
  polygonEnd: function() {
    areaStream.polygonEnd();
    boundsStream.point = boundsPoint;
    boundsStream.lineStart = boundsLineStart;
    boundsStream.lineEnd = boundsLineEnd;
    if (areaRingSum < 0) lambda0 = -(lambda1 = 180), phi0 = -(phi1 = 90);
    else if (deltaSum > epsilon) phi1 = 90;
    else if (deltaSum < -epsilon) phi0 = -90;
    range[0] = lambda0, range[1] = lambda1;
  },
  sphere: function() {
    lambda0 = -(lambda1 = 180), phi0 = -(phi1 = 90);
  }
};

function boundsPoint(lambda, phi) {
  ranges.push(range = [lambda0 = lambda, lambda1 = lambda]);
  if (phi < phi0) phi0 = phi;
  if (phi > phi1) phi1 = phi;
}

function linePoint(lambda, phi) {
  var p = cartesian([lambda * radians, phi * radians]);
  if (p0) {
    var normal = cartesianCross(p0, p),
        equatorial = [normal[1], -normal[0], 0],
        inflection = cartesianCross(equatorial, normal);
    cartesianNormalizeInPlace(inflection);
    inflection = spherical(inflection);
    var delta = lambda - lambda2,
        sign = delta > 0 ? 1 : -1,
        lambdai = inflection[0] * degrees * sign,
        phii,
        antimeridian = abs(delta) > 180;
    if (antimeridian ^ (sign * lambda2 < lambdai && lambdai < sign * lambda)) {
      phii = inflection[1] * degrees;
      if (phii > phi1) phi1 = phii;
    } else if (lambdai = (lambdai + 360) % 360 - 180, antimeridian ^ (sign * lambda2 < lambdai && lambdai < sign * lambda)) {
      phii = -inflection[1] * degrees;
      if (phii < phi0) phi0 = phii;
    } else {
      if (phi < phi0) phi0 = phi;
      if (phi > phi1) phi1 = phi;
    }
    if (antimeridian) {
      if (lambda < lambda2) {
        if (angle(lambda0, lambda) > angle(lambda0, lambda1)) lambda1 = lambda;
      } else {
        if (angle(lambda, lambda1) > angle(lambda0, lambda1)) lambda0 = lambda;
      }
    } else {
      if (lambda1 >= lambda0) {
        if (lambda < lambda0) lambda0 = lambda;
        if (lambda > lambda1) lambda1 = lambda;
      } else {
        if (lambda > lambda2) {
          if (angle(lambda0, lambda) > angle(lambda0, lambda1)) lambda1 = lambda;
        } else {
          if (angle(lambda, lambda1) > angle(lambda0, lambda1)) lambda0 = lambda;
        }
      }
    }
  } else {
    ranges.push(range = [lambda0 = lambda, lambda1 = lambda]);
  }
  if (phi < phi0) phi0 = phi;
  if (phi > phi1) phi1 = phi;
  p0 = p, lambda2 = lambda;
}

function boundsLineStart() {
  boundsStream.point = linePoint;
}

function boundsLineEnd() {
  range[0] = lambda0, range[1] = lambda1;
  boundsStream.point = boundsPoint;
  p0 = null;
}

function boundsRingPoint(lambda, phi) {
  if (p0) {
    var delta = lambda - lambda2;
    deltaSum.add(abs(delta) > 180 ? delta + (delta > 0 ? 360 : -360) : delta);
  } else {
    lambda00 = lambda, phi00 = phi;
  }
  areaStream.point(lambda, phi);
  linePoint(lambda, phi);
}

function boundsRingStart() {
  areaStream.lineStart();
}

function boundsRingEnd() {
  boundsRingPoint(lambda00, phi00);
  areaStream.lineEnd();
  if (abs(deltaSum) > epsilon) lambda0 = -(lambda1 = 180);
  range[0] = lambda0, range[1] = lambda1;
  p0 = null;
}

// Finds the left-right distance between two longitudes.
// This is almost the same as (lambda1 - lambda0 + 360°) % 360°, except that we want
// the distance between ±180° to be 360°.
function angle(lambda0, lambda1) {
  return (lambda1 -= lambda0) < 0 ? lambda1 + 360 : lambda1;
}

function rangeCompare(a, b) {
  return a[0] - b[0];
}

function rangeContains(range, x) {
  return range[0] <= range[1] ? range[0] <= x && x <= range[1] : x < range[0] || range[1] < x;
}

export default function(feature) {
  var i, n, a, b, merged, deltaMax, delta;

  phi1 = lambda1 = -(lambda0 = phi0 = Infinity);
  ranges = [];
  stream(feature, boundsStream);

  // First, sort ranges by their minimum longitudes.
  if (n = ranges.length) {
    ranges.sort(rangeCompare);

    // Then, merge any ranges that overlap.
    for (i = 1, a = ranges[0], merged = [a]; i < n; ++i) {
      b = ranges[i];
      if (rangeContains(a, b[0]) || rangeContains(a, b[1])) {
        if (angle(a[0], b[1]) > angle(a[0], a[1])) a[1] = b[1];
        if (angle(b[0], a[1]) > angle(a[0], a[1])) a[0] = b[0];
      } else {
        merged.push(a = b);
      }
    }

    // Finally, find the largest gap between the merged ranges.
    // The final bounding box will be the inverse of this gap.
    for (deltaMax = -Infinity, n = merged.length - 1, i = 0, a = merged[n]; i <= n; a = b, ++i) {
      b = merged[i];
      if ((delta = angle(a[1], b[0])) > deltaMax) deltaMax = delta, lambda0 = b[0], lambda1 = a[1];
    }
  }

  ranges = range = null;

  return lambda0 === Infinity || phi0 === Infinity
      ? [[NaN, NaN], [NaN, NaN]]
      : [[lambda0, phi0], [lambda1, phi1]];
}