// JavaScript Document

var start_stop_btn, wpid=false, map, z, op, prev_lat, prev_long, min_speed=0, max_speed=0, min_altitude=0, max_altitude=0, distance_travelled=0, min_accuracy=150, date_pos_updated="", info_string="";

// This function just adds a leading "0" to time/date components which are <10 (because there is no cross-browser way I know of to do this using the date object)
function format_time_component(time_component)
{
	if(time_component<10)
		time_component="0"+time_component;
	else if(time_component.length<2)
		time_component=time_component+"0";
		
	return time_component;
}

// This is the function which is called each time the Geo location position is updated
function geo_success(position)
{
	start_stop_btn.innerHTML="Stop"; // Set the label on the start/stop button to "Stop"
	
	info_string="";
	var d=new Date(); // Date object, used below for output messahe
	var h=d.getHours();
	var m=d.getMinutes();
	var s=d.getSeconds();
		
	var current_datetime=format_time_component(h)+":"+format_time_component(m)+":"+format_time_component(s);
	
	// Check that the accuracy of our Geo location is sufficient for our needs
	if(position.coords.accuracy<=min_accuracy)
	{
// We don't want to action anything if our position hasn't changed - we need this because on IPhone Safari at least, we get repeated readings of the same location with 
		// different accuracy which seems to count as a different reading - maybe it's just a very slightly different reading or maybe altitude, accuracy etc has changed
		if(prev_lat!=position.coords.latitude || prev_long!=position.coords.longitude)
		{
			if(position.coords.speed>max_speed)
				max_speed=position.coords.speed;
			else if(position.coords.speed<min_speed)
				min_speed=position.coords.speed;
				
			if(position.coords.altitude>max_altitude)
				max_altitude=position.coords.altitude;
			else if(position.coords.altitude<min_altitude)
				min_altitude=position.coords.altitude;
			
			
			prev_lat=position.coords.latitude;
			prev_long=position.coords.longitude;
			
			
			info_string="Current positon: lat="+position.coords.latitude+", long="+position.coords.longitude+" (accuracy "+Math.round(position.coords.accuracy, 1)+"m)<br />Speed: min="+(min_speed?min_speed:"Not recorded/0")+"m/s, max="+(max_speed?max_speed:"Not recorded/0")+"m/s<br />Altitude: min="+(min_altitude?min_altitude:"Not recorded/0")+"m, max="+(max_altitude?max_altitude:"Not recorded/0")+"m (accuracy "+Math.round(position.coords.altitudeAccuracy,1)+"m)<br />last reading taken at: "+current_datetime;
		}
	}
	else
		info_string="Accuracy not sufficient ("+Math.round(position.coords.accuracy, 1)+"m vs "+min_accuracy+"m) - last reading taken at: "+current_datetime;

	if(info_string)
		op.innerHTML=info_string;
}

// This function is called each time navigator.geolocation.watchPosition() generates an error (i.e. cannot get a Geo location reading)
function geo_error(error)
{
	switch(error.code)
	{
		case error.TIMEOUT:
			op.innerHTML="Timeout!";
		break;
	};
}


function get_pos()
{
	// Set up a watchPosition to constantly monitor the geo location provided by the browser - NOTE: !! forces a boolean response
	// We  use watchPosition rather than getPosition since it more easily allows (on IPhone at least) the browser/device to refine the geo location rather than simply taking the first available position
	// Full spec for navigator.geolocation can be foud here: http://dev.w3.org/geo/api/spec-source.html#geolocation_interface
	
	// First, check that the Browser is capable
	if(!!navigator.geolocation)
		wpid=navigator.geolocation.watchPosition(geo_success, geo_error, {enableHighAccuracy:true, maximumAge:30000, timeout:27000});
	else
		op.innerHTML="ERROR: Your Browser doesnt support the Geo Location API";
}


// Initialiser: This will find the output message div and set up the actions on the start/stop button
function init_geo()
{
	op=document.getElementById("output"); // Note the op is defined in global space and is therefore globally available
	
	if(op)
	{
		start_stop_btn=document.getElementById("geo_start_stop");
		
		if(start_stop_btn)
		{
			start_stop_btn.onclick=function()
			{
				if(wpid) // If we already have a wpid which is the ID returned by navigator.geolocation.watchPosition()
				{
					start_stop_btn.innerHTML="Start";
					navigator.geolocation.clearWatch(wpid);
					wpid=false;
				}
				else // Else...We should only ever get here right at the start of the process
				{
					start_stop_btn.innerHTML="Aquiring Geo Location...";
					get_pos();
				}
			}
			
			
		}
		else
			op.innerHTML="ERROR: Couldn't find the start/stop button";
	}
}

function getRadius(){
	
	var R = 6371; // km
	var dLat = (lat2-lat1).toRad();
	var dLon = (lon2-lon1).toRad();
	var lat1 = lat1.toRad();
	var lat2 = lat2.toRad();
	
	var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
			Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
	var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
	var d = R * c;
	
	}
	
// Initialise the whole system (above)
window.onload=init_geo;