collectgarbage()
local startStopSwitch
local startStopSwitchState=0
local altitudeSensorIndex
local distanceSensorIndex
  
local sensorLabels
local indexToSensor

local duration,sinkRate,airspeed,glideRatio={},{},{},{}
local timeStart,altitudeStart,distanceStart

local function printCell(x,y,w,text,format)
	lcd.drawText(x+(w+1-lcd.getTextWidth(format,text))/2,y,text,format)
	--lcd.drawRectangle(x,y,w+1)
	return x+w
end
local function printRow(row,text,format)
	local x,y=-1,-1+row*18
	x=printCell(x,y,80,text[1],format)
	x=printCell(x,y,80,text[2],format)
	x=printCell(x,y,80,text[3],format)
	x=printCell(x,y,80,text[4],format)
	lcd.drawLine(0,y,320,y)
end
local function printTable()
	printRow(0,{"Duration","Sink Rate","Airspeed","Glide Ratio"},FONT_BOLD)
	
	for i=1,#duration do
		local text={"-","-","-","-"}
		if duration[i]>=0 then text[1]=string.format("%d s",duration[i]) end
		if sinkRate[i]>=0 then text[2]=string.format("%.2f m/s",sinkRate[i]) end
		if airspeed[i]>=0 then text[3]=string.format("%.1f m/s",airspeed[i]) end
		if glideRatio[i]>=0 then text[4]=string.format("%.1f",glideRatio[i]) end
		printRow(i,text,FONT_NORMAL)
	end
end
local function initSensors()
	local telSensors=system.getSensors()
	sensorLabels={"..."}
	indexToSensor={0}
	for k,v in ipairs(telSensors) do
		if v.param>0 then
			table.insert(sensorLabels,v.sensorName..": "..v.label.." ["..v.unit.."]")
			table.insert(indexToSensor,k)
		end
	end
end
local function createForm(formID)
	initSensors()
	
	form.addRow(2)
	form.addLabel({label="Start/Stop Switch"})
	form.addInputbox(startStopSwitch,false,function(input) startStopSwitch=input system.pSave("startStopSwitch",startStopSwitch) end)
	form.addLabel()
	form.addLabel({label="Sensors",font=FONT_BOLD})
	form.addRow(2)
	form.addLabel({label="Altitude",width=100})
	form.addSelectbox(sensorLabels,altitudeSensorIndex,true,function(index) altitudeSensorIndex=index system.pSave("altitudeSensorIndex",altitudeSensorIndex) end,{width=212})
	form.addRow(2)
	form.addLabel({label="Distance",width=100})
	form.addSelectbox(sensorLabels,distanceSensorIndex,true,function(index) distanceSensorIndex=index system.pSave("distanceSensorIndex",distanceSensorIndex) end,{width=212})
 end
local function init(code)
	startStopSwitch=system.pLoad("startStopSwitch")
	altitudeSensorIndex=system.pLoad("altitudeSensorIndex",1)
	distanceSensorIndex=system.pLoad("distanceSensorIndex",1)
	initSensors()
	
	system.registerTelemetry(1,"Glider Performance",4,printTable)
	system.registerForm(1,MENU_APPS,"Glider Performance",createForm)	
	collectgarbage()	
end
local function loop()
	if not startStopSwitch then return end
	local startStopSwitchStateOld=startStopSwitchState
	startStopSwitchState=system.getInputsVal(startStopSwitch)

	if startStopSwitchState>0 then
		local telSensors=system.getSensors()
		local timeNow=system.getTimeCounter()
		local altitudeSensor=telSensors[indexToSensor[altitudeSensorIndex]]
		local distanceSensor=telSensors[indexToSensor[distanceSensorIndex]]
		
		if startStopSwitchStateOld<=0 then
			timeStart,altitudeStart,distanceStart=timeNow,nil,nil
			if altitudeSensor then altitudeStart=altitudeSensor.value end
			if distanceSensor then distanceStart=distanceSensor.value end
			
			table.insert(duration,1,-1)
			table.insert(sinkRate,1,-1)
			table.insert(airspeed,1,-1)
			table.insert(glideRatio,1,-1)
			
			if #duration==9 then
				table.remove(duration,9)
				table.remove(sinkRate,9)
				table.remove(airspeed,9)
				table.remove(glideRatio,9)
			end
		else
			duration[1]=(timeNow-timeStart)/1000
			if altitudeSensor and altitudeStart then sinkRate[1]=(altitudeStart-altitudeSensor.value)/duration[1] end
			if distanceSensor and distanceStart then airspeed[1]=(distanceSensor.value-distanceStart)*1000/duration[1] end
			if altitudeSensor and altitudeStart and distanceSensor and distanceStart then
				glideRatio[1]=(distanceSensor.value-distanceStart)*1000/(altitudeStart-altitudeSensor.value)
			end
		end
	end
	collectgarbage()
end

collectgarbage()
return {init=init,loop=loop,author="LD",version="1.0",name="Glider Performance"}