/**
* Written by Shane Tomlinson 2010
* http://www.shanetomlinson.com
* Released under Creative Commons Attribution Licence 3.0
* http://creativecommons.org/licenses/by/3.0/
* Uses LatLon, Spherical formulas from Chris Veness
* http://www.movable-type.co.uk/scripts/latlong.html
*/

/**
* Finds distance distanceMarkers on a line defined by a series of points.
* @class DistanceMarkerPointsCalculator
*/
function DistanceMarkerPointsCalculator() {
}

DistanceMarkerPointsCalculator.prototype = {
	init: function( config ) {
		this.latLons = [];
		if( config && config.line ) {
			this.loadLine( config.line );
		}
	},
	
	loadLine: function( line ) {
		// overload for specific source like GMaps, Yahoo maps, etc.
		// overridden function should create a LatLng and add it via addLatLon
	},

	/**
	* Add a LatLon point representing a point on the line.
	* @method addLatLon
	* @param {object} latLon - LatLon object
	*/
	addLatLon: function(latLon)
	{
	    this.latLons.push(latLon);
	},
	
	/**
	* convert a LatLon to a point that we can use in our own application.
	* @method latLonToDistanceMarker
	* @param {object} latLon - LatLon object
	* @return {object} - point we can use in our application.
	*/
	latLonToDistanceMarker: function(latLon)
	{
	    // overload to convert from a LatLon to create a distance marker point.
	    return latLon;
	},
	
	/**
	* Gets the distance marker points, each point having a lat and lng field.
	* @method getDistanceMarkerPoints
	* @param {number} distanceBetweenMarkers - distance in kilometers between distanceMarkers.
	*/
	getDistanceMarkerPoints: function(distanceBetweenMarkers)
	{
	    var distanceMarkers = [];
	    var startLatLon = this.latLons[0];
	    var distanceSinceLastMarker = 0;
		
	    // Basic idea is to keep passing points until we have gone too far.
	    // Once we have gone too far, fill in all the points up to the current
	    // location.  Repeat.
	    for (var index=1, latLon; latLon = this.latLons[index]; ++index)
	    {
		distanceSinceLastMarker += parseFloat(startLatLon.distanceTo(latLon, 6));
		var currPoint = latLon;
		var bearingToStartLatLon = currPoint.bearingTo(startLatLon);
		while (distanceSinceLastMarker > distanceBetweenMarkers)
		{
		    var distanceToMarker = distanceSinceLastMarker - distanceBetweenMarkers;
		    var markerLatLon = currPoint.destinationPoint(bearingToStartLatLon, distanceToMarker);
		    var distanceMarker = this.latLonToDistanceMarker(markerLatLon);
		    distanceMarkers.push(distanceMarker);
		    distanceSinceLastMarker = distanceToMarker;
		}
		startLatLon = latLon;
	    }
	    return distanceMarkers;
	}
};