collectgarbage()
local sensorID,sensorParam
local stepSize
local resetSwitch

local altitudeStep=0
local altitudeGained=0
local resetSwitchState

local function printForm(formID)
	local telSensors=system.getSensors()
	local sensorIDs={0}
	local sensorParams={0}
	local sensorLabels={"..."}
	local sensorIndex=0
	for k,v in ipairs(telSensors) do
		if v.param>0 then
			table.insert(sensorIDs,v.id)
			table.insert(sensorParams,v.param)
			table.insert(sensorLabels,v.sensorName..": "..v.label.." ["..v.unit.."]")
			if (sensorID==v.id and sensorParam==v.param) then sensorIndex=k end
		end
	end

	form.addRow(2)
	form.addLabel({label="Sensor",width=80})
	form.addSelectbox(sensorLabels,sensorIndex,true,function(i) sensorID=sensorIDs[i] sensorParam=sensorParams[i] system.pSave("sensorID",sensorID) system.pSave("sensorParam",sensorParam) end,{width=232})
	form.addRow(2)
	form.addLabel({label="Step Size"})
	form.addIntbox(stepSize,1,50,10,0,1,function(i) stepSize=i system.pSave("stepSize",stepSize) end)
	form.addRow(2)
	form.addLabel({label="Reset Switch"})
	form.addInputbox(resetSwitch,true,function(i) resetSwitch=i system.pSave("resetSwitch",resetSwitch) end)
 end
local function init(code)
	sensorID=system.pLoad("sensorID",0)
	sensorParam=system.pLoad("sensorParam",0)
	stepSize=system.pLoad("stepSize",10)
	resetSwitch=system.pLoad("resetSwitch")
	
	system.registerTelemetry(1,"Altitude Gain",0,function() lcd.drawText(5,0,altitudeGained.."m",FONT_BIG) end)
	system.registerForm(1,MENU_APPS,"Altitude Gain",printForm)
end
local function loop()
	local sensor=system.getSensorValueByID(sensorID,sensorParam)
	if (not sensor) then return end

	if (resetSwitch) then
		local resetSwitchStateNew=system.getInputsVal(resetSwitch)
		if (resetSwitchState~=resetSwitchStateNew) then
			resetSwitchState=resetSwitchStateNew
			altitudeGained=0
		end
	end

	if (sensor.value>altitudeStep+stepSize) then
		altitudeStep=altitudeStep+stepSize
		altitudeGained=altitudeGained+stepSize
	elseif (sensor.value<altitudeStep-stepSize) then
		altitudeStep=altitudeStep-stepSize
	end
end

return {init=init,loop=loop,author="LD",version="1.0",name="Altitude Gain"}