/******************************************************************************\
  Game tick callback support
\******************************************************************************/

local registered_chips = {}
local tickrun = 0

registerCallback("destruct",function(self)
	registered_chips[self.entity] = nil
end)

__e2setcost(1)

--- If <activate> != 0 the expression will execute once every game tick
e2function void runOnTick(activate)
    if activate ~= 0 then
        registered_chips[self.entity] = true
    else
		registered_chips[self.entity] = nil
    end
end

--- Returns 1 if the current execution was caused by "runOnTick"
e2function number tickClk()
	return tickrun
end

local function Expression2TickClock()
	local ents = {}
	
	-- this additional step is needed because we cant modify registered_chips while it is being iterated.
	for entity,_ in pairs(registered_chips) do
		if entity:IsValid() then table.insert(ents, entity) end
	end
	
	tickrun = 1
	for _,entity in ipairs(ents) do
		entity:Execute()
	end
	tickrun = 0
end
hook.Add("Think", "Expression2TickClock", Expression2TickClock)
timer.Create("Expression2TickClock", 5, 0, hook.Add, "Think", "Expression2TickClock", Expression2TickClock)

__e2setcost(nil)