-- DESCRIPTION: Glue this entity to another
local U = require "scriptbank\\utillib"
local Q = require "scriptbank\\quatlib"

local deg = math.deg
local rad = math.rad

local glueEnts = {}

function glue_entity_init_name( e, name )
	glueEnts[ e ] = { state = 'init', obj = g_Entity[ e ].obj }
end

-- creates list entry by calculating offsets between entities
local function getOffs( bobj, gobj )
	local x1, y1, z1, ax1, ay1, az1 = GetObjectPosAng( bobj )
	local x2, y2, z2, ax2, ay2, az2 = GetObjectPosAng( gobj )
	
	local q1 = Q.FromEuler( rad( ax1 ), rad( ay1 ), rad( az1 ) )
	local q2 = Q.FromEuler( rad( ax2 ), rad( ay2 ), rad( az2 ) )

	local xo, yo, zo = x2 - x1, y2 - y1, z2 - z1
	-- now need to rotate the offets to what they would be if the 
	-- base object was not rotated
	q1 = Q.Conjugate( q1 )
	xo, yo, zo = U.Rotate3D( xo, yo, zo, Q.ToEuler( q1 ) )
	-- return rotated offsets and angular difference
	return { xo = xo, yo = yo, zo = zo, 
	         angQ = Q.Mul( q1 , q2 ) }
end

local function repositionGE( ge )
	local x, y, z, xa, ya, za = GetObjectPosAng( ge.gluedTo )
	xa, ya, za = rad( xa ), rad( ya ), rad( za )

	local xo, yo, zo = U.Rotate3D( ge.offs.xo, ge.offs.yo, ge.offs.zo, xa, ya, za )
	
	local nquat = Q.FromEuler( xa, ya, za )
		
	xa, ya, za = Q.ToEuler( Q.Mul( nquat, ge.offs.angQ ) )

	PositionObject( ge.obj, x + xo, y + yo, z + zo )
	RotateObject( ge.obj, deg( xa ), deg( ya ), deg( za ) )
end

local function getEntityLinks( e )
	local list = {}
	for i = 0, 9 do
		local elink = GetEntityRelationshipID( e, i )
		if elink > 0 then
			list[ #list + 1 ] = elink
		end
	end
	return list
end

function glue_entity_main( e )
	local ge = glueEnts[ e ]
	if ge == nil then return end
	
	if ge.state == 'init' then
		local links = getEntityLinks( e )
		
		if #links > 1 then
			ge.state = 'too many'
		elseif
		   #links == 0 then
			ge.state = 'unlinked'
		else
			local obj = g_Entity[ links[ 1 ] ].obj
			ge.gluedTo = obj
			ge.offs    = getOffs( obj, ge.obj )
			ge.state   = 'ready'
		end

	elseif
	   ge.state == 'too many' then
		PromptLocal( e, 'Can only be glued to one entity' )
	elseif
	   ge.state == 'unlinked' then
		PromptLocal( e, 'Not linked to anything' )
	elseif
	   ge.state == 'ready' then
		
		repositionGE( ge )
	end
end