if FirstLoad then
	XEditorSelection = {}
	XEditorSelectSingleObjects = 0
end

function selo()
	for _, obj in ipairs(XEditorSelection) do
		if IsValid(obj) then return obj end
	end
end

function editor.GetSel(permanent_only)
	local sel = {}
	for _, obj in ipairs(XEditorSelection) do
		if IsValid(obj) and (not permanent_only or obj:GetGameFlags(const.gofPermanent) ~= 0) then sel[#sel + 1] = obj end
	end
	return sel
end

function editor.IsSelected(obj)
	return IsValid(obj) and obj:GetGameFlags(const.gofEditorSelection) ~= 0
end

function editor.GetSelUniqueCollections()
	local collections, count = {}, 0
	for _, obj in ipairs(XEditorSelection) do
		if IsValid(obj) then
			local col = obj:GetRootCollection()
			if col and not collections[col] then
				collections[col] = true
				count = count + 1
			end
		end
	end
	return count, collections
end

-- Removes all child objects (as per GetEditorParentObject) for which the parent is also in the selection;
-- this makes sure that e.g. move works properly, as the parent will also move child objects
function editor.SelectionCollapseChildObjects()
	local objs = XEditorSelection
	local i, count = 1, #objs
	while i <= count do
		local obj = objs[i]
		if editor.IsSelected(obj:GetEditorParentObject()) then
			obj:ClearHierarchyGameFlags(const.gofEditorSelection)
			objs[i] = objs[count]
			objs[count] = nil
			count = count - 1
		else
			i = i + 1
		end
	end
	return objs
end

function editor.SelectionChanged(dont_notify)
	if not dont_notify then
		editor.SelectionCollapseChildObjects()
		Msg("EditorSelectionChanged", editor.GetSel())
	end
end

function editor.ClearSel(dont_notify)
	if #XEditorSelection == 0 then
		return
	end
	for _, obj in ipairs(XEditorSelection) do
		if IsValid(obj) and obj:GetGameFlags(const.gofEditorSelection) ~= 0 then
			obj:ClearHierarchyGameFlags(const.gofEditorSelection | const.gofRealTimeAnim)
		end
	end
	XEditorSelection = {}
	editor.SelectionChanged(dont_notify)
end

function editor.AddObjToSel(obj, dont_notify, force)
	if force or IsValid(obj) and obj:GetGameFlags(const.gofEditorSelection) == 0 then
		obj:SetHierarchyGameFlags(const.gofEditorSelection)
		table.insert(XEditorSelection, obj)
		editor.SelectionChanged(dont_notify)
	end
end

function editor.RemoveObjFromSel(obj, dont_notify, force)
	if force or IsValid(obj) and obj:GetGameFlags(const.gofEditorSelection) ~= 0 then
		if table.remove_value(XEditorSelection, obj) then
			obj:ClearHierarchyGameFlags(const.gofEditorSelection)
			editor.SelectionChanged(dont_notify)
		end
	end
end

function editor.AddToSel(ol, dont_notify)
	if #(ol or "") == 0 then
		return
	end
	local flags = const.gofEditorSelection
	for _, obj in ipairs(ol) do
		if IsValid(obj) and obj:GetGameFlags(flags) == 0 then
			obj:SetHierarchyGameFlags(const.gofEditorSelection)
			table.insert(XEditorSelection, obj)
		end
	end
	editor.SelectionChanged(dont_notify)
end

function editor.RemoveFromSel(ol, to_remove)
	if #XEditorSelection == 0 then
		return
	end
	
	to_remove = to_remove or {}
	local flags = const.gofEditorSelection
	for _, obj in ipairs(ol) do
		to_remove[obj] = not IsValid(obj) or obj:GetGameFlags(flags) ~= 0
	end
	
	if next(to_remove) then
		local new_sel = {}
		for _, obj in ipairs(XEditorSelection) do
			if not to_remove[obj] then
				new_sel[#new_sel + 1] = obj
			elseif IsValid(obj) then
				obj:ClearHierarchyGameFlags(flags)
			end
		end
		XEditorSelection = new_sel
		editor.SelectionChanged()
	end
end

function editor.ChangeSelWithUndoRedo(sel, dont_notify)
	XEditorUndo:BeginOp()
	editor.SetSel(sel, dont_notify)
	XEditorUndo:EndOp()
end

function editor.SetSel(sel, dont_notify)
	if #sel == 0 then
		editor.ClearSel(dont_notify)
		return
	end
	if #XEditorSelection == 0 then
		editor.AddToSel(sel, dont_notify)
		return
	end
	if table.equal_values(sel, XEditorSelection) then
		return
	end
	local flags = const.gofEditorSelection
	local prev_sel = table.validate(XEditorSelection)
	for _, obj in ipairs(prev_sel) do
		obj:ClearHierarchyGameFlags(flags)
	end
	local new_sel = {}
	for _, obj in ipairs(sel) do
		if IsValid(obj) and obj:GetGameFlags(flags) == 0 then
			obj:SetHierarchyGameFlags(flags)
			table.insert(new_sel, obj)
		end
	end
	XEditorSelection = new_sel
	editor.SelectionChanged(dont_notify)
end

function editor.DelSelWithUndoRedo()
	local sel = editor.GetSel()
	if #sel == 0 then return end
	XEditorUndo:BeginOp{ objects = sel, name = string.format("Deleted %d objects", #sel) }
	SuspendPassEditsForEditOp()
	Msg("EditorCallback", "EditorCallbackDelete", sel)
	for _, obj in ipairs(sel) do obj:delete() end
	editor.ClearSel()
	ResumePassEditsForEditOp()
	XEditorUndo:EndOp()
end

function editor.ClearSelWithUndoRedo()
	XEditorUndo:BeginOp()
	editor.ClearSel()
	XEditorUndo:EndOp()
end

function editor.MirrorSel(sel)
	local positions = {}
	for _, obj in ipairs(sel) do
		if IsValid(obj) then 
			table.insert(positions, obj:GetPos())
		end
	end
	if #positions == 0 then return end
	
	local pivot = point(0, 0, 0)
	for _, pos in ipairs(positions) do pivot = pivot + pos end
	pivot = pivot / #positions
	for _, obj in ipairs(sel) do
		if IsValid(obj) then
			obj:SetMirrored(obj:GetGameFlags(const.gofMirrored) == 0)
			local newPos = obj:GetPos()
			local distToPivot = pivot - newPos
			
			newPos = newPos:SetY(pivot:y() + distToPivot:y())
			obj:SetPos(newPos)
		end
	end
end

function editor.IsSelectionKindOf(class)
	local has_objs
	for _, obj in ipairs(XEditorSelection) do
		if IsValid(obj) then
			if not obj:IsKindOf(class) then
				return false
			end
			has_objs = true
		end
	end
	return has_objs
end