coolDown = 0
timeSinceSeen = 999
lastSeenPos = Vec(0,0,0)
lastAngle = 1

function init()	
	--Find handle to radio
	turret = FindBody("turret")
	hinge = FindJoint("hinge")
	eye = FindLight("eye")

	--Find gun position in turret local coordinate frame
	local gun = FindLocation("gun")
	local gunWorldPos = GetLocationTransform(gun).pos
	local turretTransform = GetBodyTransform(turret)
	gunLocalPos = TransformToLocalPoint(turretTransform, gunWorldPos)
	
	--Load sound from game assets
	gunSound = LoadSound("tools/gun0.ogg")
end


function canSeePlayer()
	--Use the area light transform to determine visiblity
	local t = GetLightTransform(eye)
	local origin = TransformToParentPoint(t, Vec(0, 0, 0.1))
	local forward = TransformToParentVec(t, Vec(0, 0, 1))
	
	--Direction and distance to player
	local playerPos = GetPlayerCameraTransform().pos		
	local dirToPlayer = VecNormalize(VecSub(playerPos, origin))
	local distToPlayer = VecLength(VecSub(playerPos, origin))

	--Player is seen when in front of turret and visible
	if VecDot(forward, dirToPlayer) > 0 then
		if QueryRaycast(origin, dirToPlayer, distToPlayer) then
			--Raycast hit something, that means player is not seen
			return false
		else
			--Raycast does not hit anything, player is seen!
			return true
		end
	else
		--Player behind turret
		return false
	end
end


--This function will return the signed angle to provided position. This is used
--to figure out which direction to turn the turret.
function getTurretAngleTo(pos)
	local t = GetLightTransform(eye)
	local origin = TransformToParentPoint(t, Vec(0, 0, 0.1))
	local forward = TransformToParentVec(t, Vec(0, 0, 1))
	local dirToPos = VecNormalize(VecSub(pos, origin))
	
	--Compute angle between forward directino and direction to pos
	local angle = math.acos(VecDot(forward, dirToPos))

	--Check sign of cross product y component to determine sign of angle
	if VecCross(dirToPos, forward)[2] > 0 then
		return angle
	else
		return -angle
	end
end


function fire()
	--Find world space gun position and direction using the turret transform
	local turretTransform = GetBodyTransform(turret)
	local gunWorldPos = TransformToParentPoint(turretTransform, gunLocalPos)
	local forward = TransformToParentVec(turretTransform, Vec(0, 0, -1))

	--Play sound, flash light and shoot
	PlaySound(gunSound, gunWorldPos)
	PointLight(gunWorldPos, 1, 0.8, 0.6, 5)
	Shoot(gunWorldPos, forward, "bullet")
end


function tick(dt)
	--Check if seen and remember the last seen position
	local seen = canSeePlayer()
	if seen then
		lastSeenPos = GetPlayerCameraTransform().pos
		timeSinceSeen = 0
	else
		timeSinceSeen = timeSinceSeen + dt
	end

	--Turn towards player and shoot for a while even if no longer seen
	if timeSinceSeen < 2 then
		local angle = getTurretAngleTo(lastSeenPos)

		--If the angle is small, engage the gun
		if timeSinceSeen < 1 and math.abs(angle) < 0.2 and GetPlayerHealth() > 0 then
			coolDown = coolDown - dt
			if coolDown < 0 then
				fire()
				coolDown = 0.2
			end
		end

		--Turn turret
		angle = angle * 3
		if angle < -2 then angle = -2 end
		if angle > 2 then angle = 2 end
		SetJointMotor(hinge, angle, 100)
		
		--Remember the last angle to player
		lastAngle = angle
	else
		--Player not seen, keep rotating in direction of the last known angle
		if lastAngle > 0 then
			SetJointMotor(hinge, 1, 100)
		else
			SetJointMotor(hinge, -1, 100)
		end
	end
end