local ns = oUF
local oUF = ns.oUF
assert(oUF, "oUF not loaded")

local cos, sin, sqrt2, max, atan2 = math.cos, math.sin, math.sqrt(2), math.max, math.atan2
local tinsert, tremove = table.insert, table.remove
local pi2 = 3.141592653589793 / 2

local GetPlayerMapPosition = GetPlayerMapPosition
local UnitInParty = UnitInParty
local UnitInRaid = UnitInRaid
local UnitInRange = UnitInRange
local UnitIsConnected = UnitIsConnected
local UnitIsUnit = UnitIsUnit

local _FRAMES, OnUpdateFrame = {}

local function CalculateCorner(r) return .5 + cos(r) / sqrt2, .5 + sin(r) / sqrt2 end
local function RotateTexture(texture, angle)
	local LRx, LRy = CalculateCorner(angle + 0.785398163)
	local LLx, LLy = CalculateCorner(angle + 2.35619449)
	local ULx, ULy = CalculateCorner(angle + 3.92699082)
	local URx, URy = CalculateCorner(angle - 0.785398163)

	texture:SetTexCoord(ULx, ULy, LLx, LLy, URx, URy, LRx, LRy)
end

local GetAngle = function(unit1, unit2)
	local x1, y1 = GetPlayerMapPosition(unit1)
	if x1 <= 0 and y1 <= 0 then return nil end
	local x2, y2 = GetPlayerMapPosition(unit2)
	if x2 <= 0 and y2 <= 0 then return nil end
	return -pi2 - GetPlayerFacing() - atan2(y2 - y1, x2 - x1)
end

local minThrottle = 0.02
local numArrows, inRange, unit, GPS
local Update = function(self, elapsed)
	if self.elapsed and self.elapsed > (self.throttle or minThrottle)  then
		numArrows = 0
		for _, object in next, _FRAMES do
			if object:IsShown()  then
				GPS = object.GPS
				unit = object.unit
				if unit  then
					if unit and GPS.outOfRange  then
						inRange = CheckInteractDistance(unit, 4)
					end

					if not unit or not (UnitInParty(unit) or UnitInRaid(unit)) or UnitIsUnit(unit, "player") or not UnitIsConnected(unit) or (GPS.onMouseOver and (GetMouseFocus() ~= object)) or (GPS.outOfRange and inRange)  then
						GPS:Hide()
					else
						local angle = GetAngle("player", unit)
						if angle == nil  then
							GPS:Hide()
						else
							GPS:Show()
							RotateTexture(GPS.Texture, angle)

							numArrows = numArrows + 1
						end
					end
				else
					GPS:Hide()
				end
			end
		end

		self.elapsed = 0
		self.throttle = max(minThrottle, 0.005 * numArrows)
	else
		self.elapsed = (self.elapsed or 0) + elapsed
	end
end

local Enable = function(self)
	local GPS = self.GPS
	if GPS then
		tinsert(_FRAMES, self)

		if not OnUpdateFrame then
			OnUpdateFrame = CreateFrame("Frame")
			OnUpdateFrame:SetScript("OnUpdate", function()
				Update(this, arg1)
			end)
		end

		OnUpdateFrame:Show()
		return true
	end
end

local Disable = function(self)
	local GPS = self.GPS
	if GPS then
		for k, frame in next, _FRAMES do
			if frame == self then
				tremove(_FRAMES, k)
				GPS:Hide()
				break
			end
		end

		if getn(_FRAMES) == 0 and OnUpdateFrame then
			OnUpdateFrame:Hide()
		end
	end
end

oUF:AddElement("GPS", function() end, Enable, Disable)