Overhaul kelp interactions.

Highlights:
- Added locking system to drops. Will be removed after testing.
- Expose more variables and functions. Will be finalized soon.
- Implement MC-like age and natural growth mechanics.
- Implement correct piston interactions with kelp and its surface.
- Implement correct falling node interactions for its surface.
- ABMs are now nonfunction. Will be fixed.
- Various optimizations and fixes.

mods/ITEMS/mcl_ocean/init.lua

@@ -1,3 +1,5 @@
+mcl_ocean = {}
+
 -- Prismarine (includes sea lantern)
 dofile(minetest.get_modpath(minetest.get_current_modname()).."/prismarine.lua")
 

mods/ITEMS/mcl_ocean/kelp.lua

@@ -3,9 +3,6 @@
 --
 -- TODO: In MC, you can't actually destroy kelp by bucket'ing water in the middle.
 -- However, because of the plantlike_rooted hack, we'll just allow it for now.
---
--- TODO: Currently, you lose kelp if the kelp is placed on a block and then falls.
--- This is most relevant for (red)sand and gravel.
 
 local S = minetest.get_translator("mcl_ocean")
 local mod_doc = minetest.get_modpath("doc") ~= nil
@@ -14,19 +11,28 @@ local mod_doc = minetest.get_modpath("doc") ~= nil
 -- local-ify runtime functions
 --------------------------------------------------------------------------------
 -- objects
-local registered_items = minetest.registered_items
-local registered_nodes = minetest.registered_nodes
+local mt_registered_items = minetest.registered_items
+local mt_registered_nodes = minetest.registered_nodes
 
 -- functions
+local mt_add_item = minetest.add_item
 local mt_get_item_group = minetest.get_item_group
 local mt_get_node = minetest.get_node
-local mt_set_node = minetest.set_node
-local mt_add_item = minetest.add_item
-local mt_sound_play = minetest.sound_play
-local mt_is_creative_enabled = minetest.is_creative_enabled
-local mt_is_protected = minetest.is_protected
-local mt_hash_node_position = minetest.hash_node_position
+local mt_get_node_level = minetest.get_node_level
+local mt_get_node_max_level = minetest.get_node_max_level
+local mt_get_node_or_nil = minetest.get_node_or_nil
 local mt_get_node_timer = minetest.get_node_timer
+local mt_hash_node_position = minetest.hash_node_position
+local mt_is_protected = minetest.is_protected
+local mt_set_node = minetest.set_node
+local mt_get_meta = minetest.get_meta
+
+local mt_is_creative_enabled = minetest.is_creative_enabled
+local mt_sound_play = minetest.sound_play
+
+local math_floor = math.floor
+local math_random = math.random
+local string_format = string.format
 
 -- DEBUG: functions
 local log = minetest.log
@@ -36,109 +42,218 @@ local chatlog = minetest.chat_send_all
 -- Kelp API
 --------------------------------------------------------------------------------
 
-kelp = {}
+local kelp = {}
+mcl_ocean.kelp = kelp
+
+kelp.MAX_AGE = 25
+kelp.TIMER_INTERVAL = 0.2
+
+-- The average amount of growth for kelp in a day is 2.16 (https://youtu.be/5Bp4lAjAk3I)
+-- Normally, a day lasts 20 minutes, meaning this nodetimer is executed 24000 times.
+-- Calculate probability via 2.16/24000 and we get the probability 9/100'000 or 9.0e-5
+-- NOTE: currently, we can't exactly use the same type of randomness MC does,
+-- because it has multiple complicated sets of PRNGs.
+-- kelp.RANDOM_NUMERATOR = 9
+kelp.RANDOM_NUMERATOR = 100
+kelp.RANDOM_DENOMINATOR = 100000
+
+kelp.leaf_sounds = mcl_sounds.node_sound_leaves_defaults()
+
+-- TODO: is this really necessary
+-- Lock drops to avoid duplicate drops, set after dropping detached kelp.
+kelp.lock_drop = 0
+
+-- Registrar of nodetimers, indexed by pos_hash.
+kelp.registered_nodetimers = {}
+
+-- Pool storing age, indexed by pos_hash.
+kelp.age_pool = {}
+
+
+-- is age in the growable range?
+function kelp.is_age_growable(age)
+	return age >= 0 and age < kelp.MAX_AGE
+end
+
 
 -- Is this water?
 -- Returns the liquidtype, if indeed water.
-local function is_submerged(node, nodedef)
+function kelp.is_submerged(node, def)
 	if mt_get_item_group(node.name, "water") ~= 0 then
-		return nodedef.liquidtype -- Expected only "source" and "flowing" from water liquids
+		return def.liquidtype -- Expected only "source" and "flowing" from water liquids
 	end
 	return false
 end
-kelp.is_submerged = is_submerged
 
 
 -- Is the water downward flowing?
 -- (kelp can grow/be placed inside downward flowing water)
-local function is_downward_flowing(pos, node, nodedef, is_above)
-	local result = (math.floor(node.param2 / 8) % 2) == 1
+function kelp.is_downward_flowing(pos, node, def, is_above)
+	local result = (math_floor(node.param2 / 8) % 2) == 1
 	if not (result or is_above) then
 		-- If not, also check node above.
 		-- (this is needed due a weird quirk in the definition of "downwards flowing"
 		-- liquids in Minetest)
 		local node_above = mt_get_node({x=pos.x,y=pos.y+1,z=pos.z})
-		local nodedef_above = registered_nodes[node_above.name]
-		result = is_submerged(node_above, nodedef_above)
-			or is_downward_flowing(pos, node_above, nodedef_above, true)
+		local def_above = mt_registered_nodes[node_above.name]
+		result = kelp.is_submerged(node_above, def_above)
+			or kelp.is_downward_flowing(pos, node_above, def_above, true)
 	end
 	return result
 end
-kelp.is_downward_flowing = is_downward_flowing
+
+
+-- Will node fall at that position?
+-- This only checks if a node would fall, meaning that node need not be at pos.
+function kelp.is_falling(pos, node)
+	-- NOTE: Modified from check_single_for_falling in builtin.
+	-- Please update as necessary.
+	local nodename = node.name
+
+	if mt_get_item_group(nodename, "falling_node") == 0 then
+		return false
+	end
+
+	local pos_bottom = {x = pos.x, y = pos.y - 1, z = pos.z}
+	-- get_node_or_nil: Only fall if node below is loaded
+	local node_bottom = mt_get_node_or_nil(pos_bottom)
+	local nodename_bottom = node_bottom.name
+	local def_bottom = node_bottom and mt_registered_nodes[nodename_bottom]
+	if not def_bottom then
+		return false
+	end
+
+	local same = nodename == nodename_bottom
+	-- Let leveled nodes fall if it can merge with the bottom node
+	if same and def_bottom.paramtype2 == "leveled" and
+			mt_get_node_level(pos_bottom) <
+			mt_get_node_max_level(pos_bottom) then
+		return true
+	end
+
+	-- Otherwise only if the bottom node is considered "fall through"
+	if not same and
+			(not def_bottom.walkable or def_bottom.buildable_to) and
+			(mt_get_item_group(nodename, "float") == 0 or
+			def_bottom.liquidtype == "none") then
+		return true
+	end
+
+	return false
+end
 
 
 -- Converts param2 to kelp height.
-local function get_height(param2)
-	return math.floor(param2 / 16)
+function kelp.get_height(param2)
+	return math_floor(param2 / 16)
 end
-kelp.get_height = get_height
 
 
--- Obtain pos and node of the top of kelp.
-local function get_tip(pos, node)
+-- Obtain pos and node of the tip of kelp.
+function kelp.get_tip(pos, node)
 	local size = math.ceil(node.param2 / 16)
-	local pos_top = table.copy(pos)
-	pos_top.y = pos_top.y + size
-	return pos_top, mt_get_node(pos_top)
+	local pos_tip = table.copy(pos)
+	pos_tip.y = pos_tip.y + size
+	return pos_tip, mt_get_node(pos_tip)
 end
-kelp.get_tip = get_tip
 
 
 -- Obtain position of the first kelp unsubmerged.
-local function find_unsubmerged(pos, node)
+function kelp.find_unsubmerged(pos, node)
+
 	local x,y,z = pos.x, pos.y, pos.z
-	local height = get_height(node.param2)
+	local height = kelp.get_height(node.param2)
+	local walk_pos = {x=x, z=z}
 	for i=1,height do
-		local walk_pos = {x=x, y=y + i, z=z}
-		if mt_get_item_group(mt_get_node(walk_pos).name, "water") == 0 then
-			return walk_pos
+		walk_pos.y = y + i
+		local walk_node = mt_get_node(walk_pos)
+		if mt_get_item_group(walk_node.name, "water") == 0 then
+			return walk_pos, walk_node
 		end
 	end
 	return nil
 end
-kelp.find_unsubmerged = find_unsubmerged
 
 
 -- Obtain next param2.
-local function next_param2(param2)
-	local old_param2 = param2
-	param2 = param2+16 - param2 % 16
-	return param2, param2 ~= old_param2
+function kelp.next_param2(param2)
+	return param2+16 - param2 % 16
 end
-kelp.next_param2 = next_param2
 
 
 -- Grow next kelp.
-local function next_grow(pos, node, pos_top, def_top, is_downward_flowing)
+function kelp.next_grow(pos, node, pos_tip, def_tip, downward_flowing)
+	-- Optional parameters
+	local pos_tip, def_tip = pos_tip, def_tip
+	local downward_flowing = downward_flowing
+	if pos_tip == nil and def_tip == nil then
+		local node_tip
+		pos_tip, node_tip = kelp.get_tip(pos, node)
+		def_tip = mt_registered_nodes[node_tip.name]
+		downward_flowing = kelp.is_submerged(pos_tip, node_tip)
+			and kelp.is_downward_flowing(pos_tip, node_tip, def_tip)
+	end
+
 	-- Liquid source: Grow normally.
+	local node = table.copy(node)
+	node.param2 = kelp.next_param2(node.param2)
 	mt_set_node(pos, node)
 
-	-- Flowing liquid: Grow 1 step, but also turn the top node into a liquid source.
-	if is_downward_flowing then
-		local alt_liq = def_top.liquid_alternative_source
+	-- Flowing liquid: Grow 1 step, but also turn the tip node into a liquid source.
+	if downward_flowing then
+		local alt_liq = def_tip.liquid_alternative_source
 		if alt_liq then
-			mt_set_node(pos_top, {name=alt_liq})
+			mt_set_node(pos_tip, {name=alt_liq})
 		end
 	end
 end
-kelp.next_grow = next_grow
+
+
+-- Naturally grow next kelp.
+function kelp.natural_grow(pos, node, age, pos_hash, meta)
+	-- Must grow first, then get the new meta
+	kelp.next_grow(pos, node)
+
+	-- Optional params
+	local meta = meta or mt_get_meta(pos)
+	local pos_hash = pos_hash or mt_hash_node_position(pos)
+
+	local age = age + 1
+	kelp.age_pool[pos_hash] = age
+	meta:set_int("mcl_ocean:kelp_age", age)
+
+end
 
 
 -- Drops the items for detached kelps.
-local function detach_drop(pos, height)
+function kelp.detach_drop(pos, height, pos_hash)
+	local pos_hash = pos_hash or mt_hash_node_position(pos) -- Optional params
+
+	if kelp.lock_drop > 0 then
+		minetest.log("error",
+			string_format("Duplicate drop prevented at (%d, %d, %d) with lock level %d! Please report this.",
+				pos.x, pos.y, pos.z, kelp.lock_drop))
+		return
+	end
+
 	local x,y,z = pos.x,pos.y,pos.z
 	for i=1,height do
 		mt_add_item({x=x, y=y+i, z=z}, "mcl_ocean:kelp")
 	end
+
+	-- Locks drop.
+	kelp.lock_drop = kelp.lock_drop + 1
+	return true
 end
-kelp.detach_drop = detach_drop
 
 
 -- Detach the kelp at dig_pos, and drop their items.
 -- Synonymous to digging the kelp.
 -- NOTE: this is intended for whenever kelp truly becomes segmented plants
 -- instead of rooted to the floor. Don't try to remove dig_pos.
-local function detach_dig(dig_pos, pos, node, is_drop)
+function kelp.detach_dig(dig_pos, pos, node, is_drop, pos_hash)
+	local pos_hash = pos_hash or mt_hash_node_position(pos)
+
 	local param2 = node.param2
 	-- pos.y points to the surface, offset needed to point to the first kelp.
 	local new_height = dig_pos.y - (pos.y+1)
@@ -146,52 +261,77 @@ local function detach_dig(dig_pos, pos, node, is_drop)
 	-- Digs the entire kelp: invoke after_dig_node to mt_set_node.
 	if new_height <= 0 then
 		if is_drop then
-			detach_drop(dig_pos, get_height(param2))
+			kelp.detach_drop(dig_pos, kelp.get_height(param2), pos_hash)
 		end
 		mt_set_node(pos, {
-			name=registered_nodes[node.name].node_dig_prediction,
+			name=mt_registered_nodes[node.name].node_dig_prediction,
 			param=node.param, param2=0 })
 
 	-- Digs the kelp beginning at a height
 	else
 		if is_drop then
-			detach_drop(dig_pos, get_height(param2) - new_height)
+			kelp.detach_drop(dig_pos, kelp.get_height(param2) - new_height, pos_hash)
 		end
 		mt_set_node(pos, {name=node.name, param=node.param, param2=16*new_height})
 	end
 end
-kelp.detach_dig = detach_dig
+
 
 --------------------------------------------------------------------------------
 -- Kelp callback functions
 --------------------------------------------------------------------------------
 
-local function surface_on_dig(pos, node, digger)
-	-- NOTE: if instead, kelp shouldn't drop in creative: use this instead
-	-- detach_dig(pos, pos, node,
-	-- 	not (digger and mt_is_creative_enabled(digger:get_player_name())))
-	detach_dig(pos, pos, node, true)
+-- Set this to drop kelps when
+function kelp.surface_on_dig(pos, node, digger)
+	kelp.detach_dig(pos, pos, node, true)
 end
-kelp.surface_on_dig = surface_on_dig
 
 
-local function surface_after_dig_node(pos, node)
+function kelp.surface_after_dig_node(pos, node)
 	return mt_set_node(pos, {name=registred_nodes[node.name].node_dig_prediction})
 end
-kelp.surface_after_dig_node = surface_after_dig_node
 
 
-local kelp_timers = {}
-local kelp_timers_counter = 0
-local function surface_on_timer(pos, elapsed)
+function kelp.surface_on_timer(pos, elapsed)
 	local node = mt_get_node(pos)
-	local dig_pos = find_unsubmerged(pos, node)
+	local dig_pos = kelp.find_unsubmerged(pos, node)
+	local pos_hash = mt_hash_node_position(pos)
 	if dig_pos then
-		detach_dig(dig_pos, pos, node, true)
+		kelp.detach_dig(dig_pos, pos, node, true, pos_hash)
 	end
+
+	-- Grow kelp on chance
+	if math_random(kelp.RANDOM_DENOMINATOR) - kelp.RANDOM_NUMERATOR < 0 then
+		local age = kelp.age_pool[pos_hash]
+		if kelp.is_age_growable(age) then
+			kelp.natural_grow(pos, node, age, pos_hash)
+		end
+	end
+
 	return true
 end
 
+function kelp.surface_on_destruct(pos)
+	local node = mt_get_node(pos)
+	local pos_hash = mt_hash_node_position(pos)
+
+	-- on_falling callback. Activated by pistons for falling nodes too.
+	if kelp.is_falling(pos, node) then
+		kelp.detach_drop(pos, kelp.get_height(node.param2), pos_hash)
+	end
+
+	-- Unlocks drops.
+	if kelp.lock_drop > 0 then
+		kelp.lock_drop = kelp.lock_drop - 1
+	end
+end
+
+
+function kelp.surface_on_mvps_move(pos, node, oldpos, nodemeta)
+	-- Pistons moving falling nodes will have already activated on_falling callback.
+	kelp.detach_dig(pos, pos, node, mt_get_item_group(node.name, "falling_node") ~= 1)
+end
+
 
 -- NOTE: Uncomment this to use ABMs
 -- local function surface_unsubmerged_abm(pos, node)
@@ -204,35 +344,52 @@ end
 
 
 -- NOTE: Uncomment this to use nodetimers
-local function surface_register_nodetimer(pos, node)
-	local pos_hash = mt_hash_node_position(pos)
-	if kelp_timers[pos_hash] then
-		return
+function kelp.surface_register_nodetimer(pos, node, pos_hash, meta, age)
+	-- Optional params
+	local pos_hash,meta,age = pos_hash,meta,age
+	local timer = kelp.registered_nodetimers[pos_hash]
+
+	if not timer then
+		pos_hash = pos_hash or mt_hash_node_position(pos)
+
+		timer = mt_get_node_timer(pos)
+		kelp.registered_nodetimers[pos_hash] = timer
+
+		-- Pool age to avoid meta:get* operations
+		meta = meta or mt_get_meta(pos)
+		if not age then
+			if not meta:contains("mcl_ocean:kelp_age") then
+				age = math_random(0, kelp.MAX_AGE-1)
+			else
+				age = meta:get_int("mcl_ocean:kelp_age")
+			end
+		end
+		kelp.age_pool[pos_hash] = age
+		meta:set_int("mcl_ocean:kelp_age", age)
 	end
-	local timer = mt_get_node_timer(pos)
-	kelp_timers[pos_hash] = timer
-	timer:start(0.5)
-	kelp_timers_counter = kelp_timers_counter + 1
-	chatlog("added a timer. Currently " ..tostring(kelp_timers_counter) .." timers")
-end
-kelp.surface_register_nodetiemr = surface_register_nodetimer
 
-
-local function grow_kelp(pos, node)
-	local grow
-	-- Grow kelp by 1 node length if it would grow inside water
-	node.param2, grow = next_param2(node.param2)
-	local pos_top, node_top = get_tip(pos, node)
-	local def_top = registered_nodes[node_top.name]
-	if grow and is_submerged(node_top, def_top) then
-		next_grow(pos, node, pos_top, def_top,
-			is_downward_flowing(pos_top, node_top, def_top))
+	if not timer:is_started() then
+		timer:start(kelp.TIMER_INTERVAL)
 	end
+
+	return pos_hash, meta, age
 end
-kelp.grow_kelp = grow_kelp
 
 
-local function kelp_on_place(itemstack, placer, pointed_thing)
+-- NOTE: Uncomment this to use ABMs
+-- function kelp.grow_abm(pos, node)
+-- 	-- Grow kelp by 1 node length if it would grow inside water
+-- 	node.param2 = next_param2(node.param2)
+-- 	local pos_tip, node_tip = get_tip(pos, node)
+-- 	local def_tip = mt_registered_nodes[node_tip.name]
+-- 	if is_submerged(node_tip, def_tip) then
+-- 		kelp.next_grow(pos, node, pos_tip, def_tip,
+-- 			is_downward_flowing(pos_tip, node_tip, def_tip))
+-- 	end
+-- end
+
+
+function kelp.kelp_on_place(itemstack, placer, pointed_thing)
 	if pointed_thing.type ~= "node" or not placer then
 		return itemstack
 	end
@@ -242,14 +399,15 @@ local function kelp_on_place(itemstack, placer, pointed_thing)
 	local pos_above = pointed_thing.above
 	local node_under = mt_get_node(pos_under)
 	local nu_name = node_under.name
-	local def_under = registered_nodes[nu_name]
+	local def_under = mt_registered_nodes[nu_name]
 
-	-- Allow rightclick override.
+	-- Allow rightclick to override place.
 	if def_under and def_under.on_rightclick and not placer:get_player_control().sneak then
 		return def_under.on_rightclick(pos_under, node_under,
 				placer, itemstack, pointed_thing) or itemstack
 	end
 
+	-- Protection
 	if mt_is_protected(pos_under, player_name) or
 			mt_is_protected(pos_above, player_name) then
 		minetest.log("action", player_name
@@ -260,86 +418,89 @@ local function kelp_on_place(itemstack, placer, pointed_thing)
 		return itemstack
 	end
 
-	local new_kelp = false
-	local downward_flowing = false
-	local pos_top, node_top, def_top
+
+	local pos_tip, node_tip, def_tip
+	local pos_hash, meta
+
+
+	-- Kelp must also be placed on the top/tip side of the surface/kelp
+	if pos_under.y >= pos_above.y then
+		return itemstack
+	end
 
 	-- When placed on kelp.
 	if mt_get_item_group(nu_name, "kelp") == 1 then
-		node_under.param2, new_kelp = next_param2(node_under.param2)
-		-- Kelp must not reach the height limit.
-		-- Kelp must also be placed on top of kelp to add kelp.
-		if not new_kelp or pos_under.y >= pos_above.y then
-			return itemstack
-		end
-		pos_top, node_top = get_tip(pos_under, node_under)
-		def_top = registered_nodes[node_top.name]
+		pos_tip, node_tip = kelp.get_tip(pos_under, node_under)
+		def_tip = mt_registered_nodes[node_tip.name]
+
+		pos_hash = mt_hash_node_position(pos_under)
+		meta = mt_get_meta(pos_under)
 
 	-- When placed on surface.
 	else
-		local surfaces = kelp.surfaces or surfaces
-		for _,surface in pairs(surfaces) do
-			-- Surface must support kelp
+		local new_kelp = false
+		for _,surface in pairs(kelp.surfaces) do
 			if nu_name == surface.nodename then
 				node_under.name = "mcl_ocean:kelp_" ..surface.name
-				node_under.param2 = registered_items[nu_name].place_param2 or 16
+				node_under.param2 = 0
 				new_kelp = true
 				break
 			end
 		end
-
-		-- Kelp must also be placed on top of surface to add new kelp.
-		if not new_kelp or pos_under.y >= pos_above.y then
+		-- Surface must support kelp
+		if not new_kelp then
 			return itemstack
 		end
 
-		pos_top = pos_above
-		node_top = mt_get_node(pos_above)
-		def_top = registered_nodes[node_top.name]
-
 		-- NOTE: Uncomment this to use nodetimers
 		-- Register nodetimer
-		surface_register_nodetimer(pos_under, node_under)
+		pos_hash, meta = kelp.surface_register_nodetimer(pos_under)
+
+		pos_tip = pos_above
+		node_tip = mt_get_node(pos_above)
+		def_tip = mt_registered_nodes[node_tip.name]
 	end
 
 	-- New kelp must also be submerged in water.
-	downward_flowing = is_downward_flowing(pos_top, node_top, def_top)
-	if not (is_submerged(node_top, def_top) or downward_flowing) then
+	local downward_flowing = kelp.is_downward_flowing(pos_tip, node_tip, def_tip)
+	if not (kelp.is_submerged(node_tip, def_tip) or downward_flowing) then
 		return itemstack
 	end
 
 	-- Play sound, place surface/kelp and take away an item
-	local def_node = registered_items[nu_name]
+	local def_node = mt_registered_items[nu_name]
 	if def_node.sounds then
 		mt_sound_play(def_node.sounds.place, { gain = 0.5, pos = pos_under }, true)
 	end
-	next_grow(pos_under, node_under, pos_top, def_top, downward_flowing)
+	kelp.next_grow(pos_under, node_under, pos_tip, def_tip, downward_flowing)
 	if not mt_is_creative_enabled(player_name) then
 		itemstack:take_item()
 	end
 
+	-- Reroll age
+	local age = math_random(0, kelp.MAX_AGE-1)
+	meta:set_int("mcl_ocean:kelp_age", age)
+	kelp.age_pool[pos_hash] = age
+
 	return itemstack
 end
-kelp.kelp_on_place = kelp_on_place
 
 --------------------------------------------------------------------------------
 -- Kelp registration API
 --------------------------------------------------------------------------------
 
 -- List of supported surfaces for seagrass and kelp.
-local surfaces = {
+kelp.surfaces = {
 	{ name="dirt",    nodename="mcl_core:dirt",    },
 	{ name="sand",    nodename="mcl_core:sand",    },
 	{ name="redsand", nodename="mcl_core:redsand", },
 	{ name="gravel",  nodename="mcl_core:gravel",  },
 }
-kelp.surfaces = surfaces
-local registered_surfaces = {}
-kelp.registered_surfaces = registered_surfaces
+kelp.registered_surfaces = {}
 
 -- Commented properties are the ones obtained using register_kelp_surface.
 -- If you define your own properties, it overrides the default ones.
-local surface_deftemplate = {
+kelp.surface_deftemplate = {
 	drawtype = "plantlike_rooted",
 	paramtype = "light",
 	paramtype2 = "leveled",
@@ -365,55 +526,46 @@ local surface_deftemplate = {
 	groups = { dig_immediate = 3, deco_block = 1, plant = 1, kelp = 1, },
 	--sounds = sounds,
 	--node_dig_prediction = nodename,
-	after_dig_node = surface_after_dig_node,
-	on_dig = surface_on_dig,
-	on_timer = surface_on_timer,
+	after_dig_node = kelp.surface_after_dig_node,
+	on_destruct = kelp.surface_on_destruct,
+	on_dig = kelp.surface_on_dig,
+	on_timer = kelp.surface_on_timer,
+	mesecon = { on_mvps_move = kelp.surface_on_mvps_move, },
 	drop = "", -- drops are handled in on_dig
 	--_mcl_falling_node_alternative = is_falling and nodename or nil,
 	_mcl_hardness = 0,
 	_mcl_blast_resistance = 0,
 }
-kelp.surface_deftemplate = surface_deftemplate
 
 -- Commented properties are the ones obtained using register_kelp_surface.
-local surface_docs = {
+kelp.surface_docs = {
 	-- entry_id_orig = nodename,
 	_doc_items_entry_name = S("Kelp"),
 	_doc_items_longdesc = S("Kelp grows inside water on top of dirt, sand or gravel."),
 	--_doc_items_create_entry = doc_create,
 	_doc_items_image = "mcl_ocean_kelp_item.png",
 }
-kelp.surface_docs = surface_docs
 
---[==[--
-register_kelp_surface(surface[, surface_deftemplate[, surface_docs]])
-
-surface: table with its specific properties. See also kelp.surface.
-
-surface_deftemplate: modifiable nodedef template. See also kelp.surface_deftempate.
-DO NOT RE-USE THE SAME DEFTEMPLATE. create copies.
-
-surface_docs: table with properties related to docs. See also kelp.surface_docs.
---]==]--
-local leaf_sounds = mcl_sounds.node_sound_leaves_defaults()
-local function register_kelp_surface(surface, surface_deftemplate, surface_docs)
+-- Creates new surfaces.
+-- NOTE: surface_deftemplate will be modified in-place.
+function kelp.register_kelp_surface(surface, surface_deftemplate, surface_docs)
 	local name = surface.name
 	local nodename = surface.nodename
-	local def = registered_nodes[nodename]
+	local def = mt_registered_nodes[nodename]
 	local def_tiles = def.tiles
 
 	local surfacename = "mcl_ocean:kelp_"..name
-	local surface_deftemplate = surface_deftemplate or kelp.surface_deftemplate -- optional param
+	local surface_deftemplate = surface_deftemplate or kelp.surface_deftemplate -- Optional param
 
 	local doc_create = surface.doc_create or false
-	local surface_docs = surface_docs or kelp.surface_docs
+	local surface_docs = surface_docs or kelp.surface_docs -- Optional param
 
 	if doc_create then
 		surface_deftemplate._doc_items_entry_name = surface_docs._doc_items_entry_name
 		surface_deftemplate._doc_items_longdesc = surface_docs._doc_items_longdesc
 		surface_deftemplate._doc_items_create_entry = true
 		surface_deftemplate._doc_items_image = surface_docs._doc_items_image
-		-- Takes the first surface with docs
+		-- Sets the first surface as the docs' entry ID
 		if not surface_docs.entry_id_orig then
 			surface_docs.entry_id_orig = nodename
 		end
@@ -422,9 +574,9 @@ local function register_kelp_surface(surface, surface_deftemplate, surface_docs)
 	end
 
 	local sounds = table.copy(def.sounds)
-	sounds.dig = leaf_sounds.dig
-	sounds.dug = leaf_sounds.dug
-	sounds.place = leaf_sounds.place
+	sounds.dig = kelp.leaf_sounds.dig
+	sounds.dug = kelp.leaf_sounds.dug
+	sounds.place = kelp.leaf_sounds.place
 
 	surface_deftemplate.tiles = surface_deftemplate.tiles or def_tiles
 	surface_deftemplate.inventory_image = surface_deftemplate.inventory_image or "("..def_tiles[1]..")^mcl_ocean_kelp_item.png"
@@ -440,9 +592,9 @@ end
 -- Kelp surfaces nodes ---------------------------------------------------------
 
 -- Dirt must be registered first, for the docs
-register_kelp_surface(surfaces[1], table.copy(surface_deftemplate), surface_docs)
-for i=2, #surfaces do
-	register_kelp_surface(surfaces[i], table.copy(surface_deftemplate), surface_docs)
+kelp.register_kelp_surface(kelp.surfaces[1], table.copy(kelp.surface_deftemplate), kelp.surface_docs)
+for i=2, #kelp.surfaces do
+	kelp.register_kelp_surface(kelp.surfaces[i], table.copy(kelp.surface_deftemplate), kelp.surface_docs)
 end
 
 -- Kelp item -------------------------------------------------------------------
@@ -453,12 +605,12 @@ minetest.register_craftitem("mcl_ocean:kelp", {
 	_doc_items_create_entry = false,
 	inventory_image = "mcl_ocean_kelp_item.png",
 	wield_image = "mcl_ocean_kelp_item.png",
-	on_place = kelp_on_place,
+	on_place = kelp.kelp_on_place,
 	groups = { deco_block = 1 },
 })
 
 if mod_doc then
-	doc.add_entry_alias("nodes", surface_docs.entry_id_orig, "craftitems", "mcl_ocean:kelp")
+	doc.add_entry_alias("nodes", kelp.surface_docs.entry_id_orig, "craftitems", "mcl_ocean:kelp")
 end
 
 -- Dried kelp ------------------------------------------------------------------
@@ -523,26 +675,17 @@ minetest.register_craft({
 })
 
 -- ABMs ------------------------------------------------------------------------
-minetest.register_abm({
-	label = "Kelp growth",
-	nodenames = { "group:kelp" },
-	interval = 45,
-	chance = 12,
-	catch_up = false,
-	action = grow_kelp,
-})
 
 -- NOTE: Uncomment this to use nodetimers
 minetest.register_lbm({
 	label = "Kelp timer registration",
 	name = "mcl_ocean:kelp_timer_registration",
 	nodenames = { "group:kelp" },
-	run_at_every_load = false,
-	action = surface_register_nodetimer,
+	run_at_every_load = true, -- so old kelps are also registered
+	action = kelp.surface_register_nodetimer,
 })
 
 -- NOTE: Uncomment this to use ABMs
--- Break kelp not underwater.
 -- minetest.register_abm({
 -- 	label = "Kelp drops",
 -- 	nodenames = { "group:kelp" },
@@ -551,3 +694,12 @@ minetest.register_lbm({
 -- 	catch_up = false,
 -- 	action = surface_unsubmerged_abm,
 -- })
+--
+-- minetest.register_abm({
+-- 	label = "Kelp growth",
+-- 	nodenames = { "group:kelp" },
+-- 	interval = 45,
+-- 	chance = 12,
+-- 	catch_up = false,
+-- 	action = grow_abm,
+-- })