Mushroom spread: Optimise and make overridable

Move mushroom spread ABM action into a global and overridable function.
Optimise spread code.
Reduce spread range to reduce spread through walls.

mods/flowers/init.lua

@@ -204,38 +204,34 @@ minetest.register_node("flowers:mushroom_brown", {
 
 -- Mushroom spread and death
 
-minetest.register_abm({
+function flowers.mushroom_spread(pos, node)
-	label = "Mushroom spread",
-	nodenames = {"flowers:mushroom_brown", "flowers:mushroom_red"},
-	interval = 11,
-	chance = 50,
-	action = function(pos, node)
 	if minetest.get_node_light(pos, nil) == 15 then
 		minetest.remove_node(pos)
 		return
 	end
-		local random = {
+	local positions = minetest.find_nodes_in_area_under_air(
-			x = pos.x + math.random(-2, 2),
+		{x = pos.x - 1, y = pos.y - 2, z = pos.z - 1},
-			y = pos.y + math.random(-1, 1),
+		{x = pos.x + 1, y = pos.y + 1, z = pos.z + 1},
-			z = pos.z + math.random(-2, 2)
+		{"group:soil", "group:tree"})
-		}
+	if #positions == 0 then
-		local random_node = minetest.get_node_or_nil(random)
-		if not random_node or random_node.name ~= "air" then
 		return
 	end
-		local node_under = minetest.get_node_or_nil({x = random.x,
+	local pos2 = positions[math.random(#positions)]
-			y = random.y - 1, z = random.z})
+	pos2.y = pos2.y + 1
-		if not node_under then
+	if minetest.get_node_light(pos, 0.5) <= 3 and
-			return
+			minetest.get_node_light(pos2, 0.5) <= 3 then
+		minetest.set_node(pos2, {name = node.name})
 	end
+end
 
-		if (minetest.get_item_group(node_under.name, "soil") ~= 0 or
+minetest.register_abm({
-				minetest.get_item_group(node_under.name, "tree") ~= 0) and
+	label = "Mushroom spread",
-				minetest.get_node_light(pos, 0.5) <= 3 and
+	nodenames = {"flowers:mushroom_brown", "flowers:mushroom_red"},
-				minetest.get_node_light(random, 0.5) <= 3 then
+	interval = 11,
-			minetest.set_node(random, {name = node.name})
+	chance = 150,
-		end
+	action = function(...)
-	end
+		flowers.mushroom_spread(...)
+	end,
 })