/*
 * Call generic wms service for GoogleMaps v2
 * John Deck, UC Berkeley
 * Inspiration & Code from:
 *      Mike Williams http://www.econym.demon.co.uk/googlemaps2/ V2 Reference & custommap code
 *      Brian Flood http://www.spatialdatalogic.com/cs/blogs/brian_flood/archive/2005/07/11/39.aspx V1 WMS code
 *      Kyle Mulka http://blog.kylemulka.com/?p=287  V1 WMS code modifications
 *      http://search.cpan.org/src/RRWO/GPS-Lowrance-0.31/lib/Geo/Coordinates/MercatorMeters.pm
 * 		Modified by Chris Holmes, TOPP to work by default with GeoServer.
 *		Guilhem Vellut <guilhem.vellut@gmail.com> for more accurate Javascript Mercator Fxn
 *
 * Note this only works with gmaps v2.36 and above.  http://johndeck.blogspot.com
 * has scripts
 * that do the same for older gmaps versions - just change from 54004 to 41001.
 *
 * About:
 * This script provides an implementation of GTileLayer that works with WMS
 * services that provide epsg 41001 (Mercator).  This provides a reasonable
 * accuracy on overlays at most zoom levels.  It switches between Mercator
 * and Lat/Long at the myMercZoomLevel variable, defaulting to MERC_ZOOM_DEFAULT
 * of 5.  It also performs the calculation from a GPoint to the appropriate
 * BBOX to pass the WMS.  The overlays could be more accurate, and if you
 * figure out a way to make them so please contribute information back to
 * http://docs.codehaus.org/display/GEOSDOC/Google+Maps.  There is much
 * information at:
 * http://cfis.savagexi.com/articles/2006/05/03/google-maps-deconstructed
 *
 * Use:
 * This script is used by creating a new GTileLayer, setting the required
 * and any desired optional variables, and setting the functions here to
 * override the appropriate GTileLayer ones.
 *
 * At the very least you will need:
 * var myTileLayer= new GTileLayer(new GCopyrightCollection(""),1,17);
 *     myTileLayer.myBaseURL='http://yourserver.org/wms?'
 *     myTileLayer.myLayers='myLayerName';
 *     myTileLayer=CustomGetTileUrl
 *
 * After that you can override the format (myFormat), the level at
 * which the zoom switches (myMercZoomLevel), and the style (myStyles)
 * - be sure to put one style for each layer (both are separated by
 * commas).  You can also override the Opacity:
 *     myTileLayer.myOpacity=0.69
 *     myTileLayer.getOpacity=customOpacity
 *
 * Then you can overlay on google maps with something like:
 * var layer=[G_SATELLITE_MAP.getTileLayers()[0],tileCountry];
 * var custommap = new GMapType(layer, G_SATELLITE_MAP.getProjection(), "WMS");
 * var map = new GMap(document.getElementById("map"));
 *     map.addMapType(custommap);
 */

var MAGIC_NUMBER = 6356752.3142;
var WGS84_SEMI_MAJOR_AXIS = 6378137.0;
var WGS84_ECCENTRICITY = 0.0818191913108718138;
var DEG2RAD = 0.0174532922519943;
var PI = 3.14159267;

//Default image format, used if none is specified
var FORMAT_DEFAULT = 'PNG';

//Google Maps Zoom level at which we switch from Mercator to Lat/Long.
var MERC_ZOOM_DEFAULT = 15;

function dd2MercMetersLng(p_lng) 
{
	return WGS84_SEMI_MAJOR_AXIS * (p_lng * DEG2RAD);
}

function dd2MercMetersLat(p_lat) 
{
	var lat_rad = p_lat * DEG2RAD;
	return WGS84_SEMI_MAJOR_AXIS * Math.log(Math.tan((lat_rad + PI / 2) / 2) * Math.pow( ((1 - WGS84_ECCENTRICITY * Math.sin(lat_rad)) / (1 + WGS84_ECCENTRICITY * Math.sin(lat_rad))), (WGS84_ECCENTRICITY/2)));
}

CustomGetTileUrl = function(a, b, c) 
{
	if (this.myMercZoomLevel == undefined) 
	{
    	this.myMercZoomLevel = MERC_ZOOM_DEFAULT;
	}
	if (this.myFormat == undefined) 
	{
    	this.myFormat = FORMAT_DEFAULT;
	}
	if (typeof(window['this.myStyles']) == 'undefined') 
	{
		this.myStyles = '';
	}
	var lULP = new GPoint(a.x * 256, (a.y + 1) * 256);
	var lLRP = new GPoint((a.x + 1) * 256, a.y * 256);
	var lUL = G_NORMAL_MAP.getProjection().fromPixelToLatLng(lULP, b, c);
	var lLR = G_NORMAL_MAP.getProjection().fromPixelToLatLng(lLRP, b, c);

	// switch between Mercator and DD if merczoomlevel is set
	// NOTE -it is now safe to use Mercator exclusively for all zoom levels (if your WMS supports it)
	// so you can just use the two lines of code below the IF (& delete the ELSE)
	// drg & doq are topozone layers--- they don't work with epsg:54004
	
	var coordMin = ToUtm(lUL.y, lUL.x)
	var coordMax = ToUtm(lLR.y, lLR.x)
	
	var xMin = coordMin[0];
	var yMin = coordMin[1];
	var xMax = coordMax[0];
	var yMax = coordMax[1];
	
	//var lBbox = lUL.x + ',' + lUL.y + ',' + lLR.x + ',' + lLR.y;
	var lBbox = xMin + ';' + yMin + ';' + xMax + ';' + yMax;
	
	//var lSRS = 'EPSG:4326';
	//var lSRS = 'EPSG:32632';

	var lURL = this.myBaseURL;
	lURL += 'req=getimage';
	lURL += '&service=Orchidea';
	lURL += '&box=' + lBbox;
	lURL += '&layers=' + this.myLayers;
	return lURL;
}

function customOpacity() { return this.myOpacity; }

function GetImageUrl(lURL)
{
	MakeRequest(lURL);
}

function GetXmlHttp()
{
	var xmlhttp = false;
	if (!xmlhttp && typeof XMLHttpRequest != 'undefined') 
	{
		try 
		{
			xmlhttp = new XMLHttpRequest();
		} 
		catch (e) 
		{
			xmlhttp = false;
		}
	}
	if (!xmlhttp && window.createRequest) 
	{
		try 
		{
			xmlhttp = window.createRequest();
		} 
		catch (e) 
		{
			xmlhttp = false;
		}
	}
	return xmlhttp;
}

function MakeRequest(url) 
{
	/*try 
	{
		netscape.security.PrivilegeManager.enablePrivilege('UniversalBrowserRead');
	} 
	catch (e) 
	{
		alert('Permission UniversalBrowserRead denied.');
	}*/
    var http_request = false;
    http_request = GetXmlHttp();
    if (http_request.overrideMimeType)
	{
		http_request.overrideMimeType('text/xml');
    }
    if (!http_request) 
	{
		alert('Cannot create XMLHTTP instance');
		return false;
    }
    http_request.onreadystatechange = AlertContents;
    http_request.open('GET', url, false);
    //http_request.send(null);
}

function AlertContents(http_request) 
{
	var response = '';
    if (http_request.readyState == 4) 
	{
		if (http_request.status == 200) 
		{
			response = http_request.responseText;	
			alert(response);
		} 
		else 
		{
			alert('There was a problem with the request.');
		}
    }
	return response;
}