-- LUA Script - precede every function and global member with lowercase name of script + '_main'
local rad  = math.rad
local deg  = math.deg
local atan = math.atan2
local sqrt = math.sqrt

local Q = require "scriptbank\\quatlib"

local facingEnts = {}
local rotated    = {}

function facing_init(e)
	Include("quatlib.lua")
end

function FindFacing( ommitting )
	-- return first entity in list that isn't the one specified
	for k, v in pairs( facingEnts ) do
		if v and k ~= ommitting then return k end
	end
end

function facing_main(e)
	local thisEnt = facingEnts[e]
	
	if thisEnt == nil then
		facingEnts[e] = true
		return
		
	elseif not rotated[ e ] then
	
		local otherEnt = FindFacing( e )

		if otherEnt == nil then return end
		
		-- rotate to face it
		local oEnt = g_Entity[ otherEnt ]
		local tEnt = g_Entity[ e ]
		
		local myQ = Q.FromEuler( 0, 0, 0 ) -- our default direction

		-- now work out the angles from us to them
		local DX, DZ = oEnt.x - tEnt.x, oEnt.z - tEnt.z
		local yAng = atan( DX, DZ )
		local DY = oEnt.y - tEnt.y
		
		local xAng = -atan( DY, sqrt( DX*DX + DZ*DZ ) )
		
		myQ = Q.Mul( myQ, Q.FromEuler(    0, yAng,    0 ) )
		myQ = Q.Mul( myQ, Q.FromEuler( xAng,    0,    0 ) )
				
		local xr, yr, zr = Q.ToEuler( myQ )		
	
		CollisionOff( e )
		SetRotation(   e, deg(xr), deg(yr), deg(zr) )
		ResetRotation( e, deg(xr), deg(yr), deg(zr) )
		CollisionOff( e )
		
		rotated[ e ] = true
	end
end