/*
	Copyright (c) 2017 Jean-Marc VIGLINO, 
	released under the CeCILL-B license (http://www.cecill.info/).
	
	ol.coordinate.convexHull compute a convex hull using Andrew's Monotone Chain Algorithm.
	
	@see https://en.wikipedia.org/wiki/Convex_hull_algorithms
*/

import ol_geom_Geometry from 'ol/geom/geometry'

(function(){

/* Tests if a point is left or right of line (a,b).
* @param {ol.coordinate} a point on the line
* @param {ol.coordinate} b point on the line
* @param {ol.coordinate} 0
* @return {bool} true if (a,b,o) turns clockwise
*/
function clockwise (a, b, o) 
{	return ( (a[0] - o[0]) * (b[1] - o[1]) - (a[1] - o[1]) * (b[0] - o[0]) <= 0 )
}

/** Compute a convex hull using Andrew's Monotone Chain Algorithm
* @param {Array<ol.geom.Point>} points an array of 2D points 
* @return {Array<ol.geom.Point>} the convex hull vertices
*/
var ol_coordinate_convexHull = function (points)
{	// Sort by increasing x and then y coordinate
	points.sort(function(a, b) 
	{	return a[0] == b[0] ? a[1] - b[1] : a[0] - b[0];
	});

    // Compute the lower hull 
	var lower = [];
	for (var i = 0; i < points.length; i++) 
	{	while (lower.length >= 2 && clockwise (lower[lower.length - 2], lower[lower.length - 1], points[i]) ) 
		{	lower.pop();
		}
		lower.push(points[i]);
	}

    // Compute the upper hull 
	var upper = [];
	for (var i = points.length - 1; i >= 0; i--) 
	{	while (upper.length >= 2 && clockwise (upper[upper.length - 2], upper[upper.length - 1], points[i]) ) 
		{	upper.pop();
		}
		upper.push(points[i]);
	}

	upper.pop();
	lower.pop();
	return lower.concat(upper);
}

/* Get coordinates of a geometry */
function getCoordinates(geom)
{	var h = [];
	switch (geom.getType())
	{	case "Point":
			h.push(geom.getCoordinates());
			break;
		case "LineString":
		case "LinearRing":
		case "MultiPoint":
			 h = geom.getCoordinates();
			break;
		case "MultiLineString":
			var p = geom.getLineStrings();
			for (var i=0; i<p.length; i++) h.concat(getCoordinates(p[i]));
			break;
		case "Polygon":
			h = getCoordinates(geom.getLinearRing(0));
			break;
		case "MultiPolygon":
			var p = geom.getPolygons();
			for (var i=0; i<p.length; i++) h.concat(getCoordinates(p[i]));
			break;
		case "GeometryCollection":
			var p = geom.getGeometries();
			for (var i=0; i<p.length; i++) h.concat(getCoordinates(p[i]));
			break;
		default:break;
	}
	return h;
}

/** Compute a convex hull on a geometry using Andrew's Monotone Chain Algorithm
* @return {Array<ol.geom.Point>} the convex hull vertices
*/
ol_geom_Geometry.prototype.convexHull = function()
{	return ol_coordinate_convexHull( getCoordinates(this) );
};


})();