// https://d3js.org/d3-polygon/ v1.0.5 Copyright 2018 Mike Bostock
(function (global, factory) {
typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
typeof define === 'function' && define.amd ? define(['exports'], factory) :
(factory((global.d3 = global.d3 || {})));
}(this, (function (exports) { 'use strict';

function area(polygon) {
  var i = -1,
      n = polygon.length,
      a,
      b = polygon[n - 1],
      area = 0;

  while (++i < n) {
    a = b;
    b = polygon[i];
    area += a[1] * b[0] - a[0] * b[1];
  }

  return area / 2;
}

function centroid(polygon) {
  var i = -1,
      n = polygon.length,
      x = 0,
      y = 0,
      a,
      b = polygon[n - 1],
      c,
      k = 0;

  while (++i < n) {
    a = b;
    b = polygon[i];
    k += c = a[0] * b[1] - b[0] * a[1];
    x += (a[0] + b[0]) * c;
    y += (a[1] + b[1]) * c;
  }

  return k *= 3, [x / k, y / k];
}

// Returns the 2D cross product of AB and AC vectors, i.e., the z-component of
// the 3D cross product in a quadrant I Cartesian coordinate system (+x is
// right, +y is up). Returns a positive value if ABC is counter-clockwise,
// negative if clockwise, and zero if the points are collinear.
function cross(a, b, c) {
  return (b[0] - a[0]) * (c[1] - a[1]) - (b[1] - a[1]) * (c[0] - a[0]);
}

function lexicographicOrder(a, b) {
  return a[0] - b[0] || a[1] - b[1];
}

// Computes the upper convex hull per the monotone chain algorithm.
// Assumes points.length >= 3, is sorted by x, unique in y.
// Returns an array of indices into points in left-to-right order.
function computeUpperHullIndexes(points) {
  var n = points.length,
      indexes = [0, 1],
      size = 2;

  for (var i = 2; i < n; ++i) {
    while (size > 1 && cross(points[indexes[size - 2]], points[indexes[size - 1]], points[i]) <= 0) --size;
    indexes[size++] = i;
  }

  return indexes.slice(0, size); // remove popped points
}

function hull(points) {
  if ((n = points.length) < 3) return null;

  var i,
      n,
      sortedPoints = new Array(n),
      flippedPoints = new Array(n);

  for (i = 0; i < n; ++i) sortedPoints[i] = [+points[i][0], +points[i][1], i];
  sortedPoints.sort(lexicographicOrder);
  for (i = 0; i < n; ++i) flippedPoints[i] = [sortedPoints[i][0], -sortedPoints[i][1]];

  var upperIndexes = computeUpperHullIndexes(sortedPoints),
      lowerIndexes = computeUpperHullIndexes(flippedPoints);

  // Construct the hull polygon, removing possible duplicate endpoints.
  var skipLeft = lowerIndexes[0] === upperIndexes[0],
      skipRight = lowerIndexes[lowerIndexes.length - 1] === upperIndexes[upperIndexes.length - 1],
      hull = [];

  // Add upper hull in right-to-l order.
  // Then add lower hull in left-to-right order.
  for (i = upperIndexes.length - 1; i >= 0; --i) hull.push(points[sortedPoints[upperIndexes[i]][2]]);
  for (i = +skipLeft; i < lowerIndexes.length - skipRight; ++i) hull.push(points[sortedPoints[lowerIndexes[i]][2]]);

  return hull;
}

function contains(polygon, point) {
  var n = polygon.length,
      p = polygon[n - 1],
      x = point[0], y = point[1],
      x0 = p[0], y0 = p[1],
      x1, y1,
      inside = false;

  for (var i = 0; i < n; ++i) {
    p = polygon[i], x1 = p[0], y1 = p[1];
    if (((y1 > y) !== (y0 > y)) && (x < (x0 - x1) * (y - y1) / (y0 - y1) + x1)) inside = !inside;
    x0 = x1, y0 = y1;
  }

  return inside;
}

function length(polygon) {
  var i = -1,
      n = polygon.length,
      b = polygon[n - 1],
      xa,
      ya,
      xb = b[0],
      yb = b[1],
      perimeter = 0;

  while (++i < n) {
    xa = xb;
    ya = yb;
    b = polygon[i];
    xb = b[0];
    yb = b[1];
    xa -= xb;
    ya -= yb;
    perimeter += Math.sqrt(xa * xa + ya * ya);
  }

  return perimeter;
}

exports.polygonArea = area;
exports.polygonCentroid = centroid;
exports.polygonHull = hull;
exports.polygonContains = contains;
exports.polygonLength = length;

Object.defineProperty(exports, '__esModule', { value: true });

})));
