blockgame/mods/bg_tree/decompose.lua

local modname = minetest.get_current_modname()
local api = blockgame.tree
local vec = blockgame.vector

-- NODE NAMES

local leaves = modname .. ":leaves"
local leaves_decomposing = modname .. ":leaves_decomposing"

-- END OF NODE NAMES

blockgame.register_increasing_abm({
	id = modname .. ":begin_decompose",
	label = "decompose leaves",
	nodenames = {leaves},
	neighbors = {"group:dirty", leaves_decomposing},
	interval = 15,
	chance = 4,
	rate = function (pos, node, data)
		return data.value + math.random(4, 6)
	end,
	check = function (pos, node, data)
		return data.value >= 20
	end,
	action = function (pos, node, data)
		minetest.set_node(pos, {name = leaves_decomposing})
	end,
})

local decompose_scores = {
	dirty = 50,
	leaves_decomposing = 30,
}

local decompose_cost = 2000

blockgame.register_increasing_abm({
	id = modname .. ":decompose",
	label = "decompose leaves",
	nodenames = {"group:leaves_decomposing"},
	-- neighbors = {"group:dirty", "group:leaves_decomposing"},
	interval = 30,
	chance = 10,
	rate = function (pos, node, data)
		local score = 100

		local source_pos = pos
		blockgame.flood_fill(pos, function (pos, distance)
			if pos == source_pos then return true end

			local name = minetest.get_node(pos).name

			local gain = 0
			for group, value in pairs(decompose_scores) do
				local group = minetest.get_item_group(name, group)
				if group > 0 then
					gain = math.max(gain, value * group)
				end
			end

			gain = math.floor(gain / distance)

			if gain > 0 then
				score = score + gain
				return true
			end

			return false
		end, 4)

		return data.value + score
	end,
	check = function (pos, node, data)
		return data.value >= decompose_cost
	end,
	action = function (pos, node, data)
		-- currently, larger leaf piles have a greater chance of turning into dirt instead of disappearing.
		-- might wanna make it so that instead, dirt is layered as well?
		local def = minetest.registered_nodes[node.name]
		local dirt_chance = def.level_max - def.level + 1

		if blockgame.chance(dirt_chance) then
			minetest.set_node(pos, {name = "bg_terrain:dirt"})
		else
			minetest.remove_node(pos)
		end
	end,
})