script.on_init(function ()
	global = {}
	global.next_ID = 1
	global.last_tick = 0
	global.trees = nil
	
	
	for chunk in game.surfaces[1].get_chunks() do
		trees_of_area_to_table ({{(chunk.x*32), (chunk.y*32)},{(chunk.x*32+32), (chunk.y*32+32)}})
	end
end)


script.on_event(defines.events.on_chunk_generated, function (event)
	local area = event.area
	trees_of_area_to_table (area)
end)


script.on_event(defines.events.on_tick, function (event)
	local cur = global.trees;
	while cur do
		cur.age_ticks = cur.age_ticks + 1
		cur = cur.next;
	end
	if (game.tick % 600 == 0) then 
		log ("game.tick = " .. game.tick .. " Trees: " .. global.next_ID) 
	end
end)


function trees_of_area_to_table (area, surface)
	local surface = surface or game.surfaces[1]
	--find_entities_filtered{area=…, position=…, name=…, type=…, force=…, limit=…}
	local trees = surface.find_entities_filtered{area=area, type="tree"}
	if not trees then return end
	for i, tree in pairs (trees) do
		global.trees = {next=global.trees, age_ticks = 0, entity = tree}
		global.next_ID = global.next_ID+1;
	end
end


function printAll(text)
	if type(text) == "table" then text = serpent.block(text, {comment = false}) end
	for player_index, player in pairs (game.players) do game.players[player_index].print (text) end
end