node_damage/init.lua

--[[
Node Damage and Repair System
Copyright (C) 2020 Noodlemire

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
--]]

--mod-specific global storage
node_damage = {}

--Get mod-private storage, which is used to remember what nodes will exist.
local store = minetest.get_mod_storage()

--A list of nodes to define. Nodes added by this mod are initialized with an empty definition,
--so that override_item can be used when all other nodes are registered.
local queue = {}

--Get the node_damage version of an item's name.
--In the original name, the comma is gsubbed into an underscore in order to comply with naming standards.
local function get_node_damage_name(name, i)
	return "node_damage:"..(name:gsub(":", "_")).."_"..i
end

--For each item name that was previously saved...
for name in pairs(store:to_table().fields) do
	--Add it to the queue.
	queue[name] = true

	--Also, add the three other stages of cracking to the queue after registering them with blank definitions.
	for i = 1, 3 do
		minetest.register_node(get_node_damage_name(name, i), {})
		queue[get_node_damage_name(name, i)] = true
	end
end

--Check if any particular node is valid for crackification.
local function node_is_valid(name, can_be_in_queue)
	--Get the existing definition for this item.
	local def = minetest.registered_items[name]

	--If this item isn't in the queue, it is nil, rather than false.
	--So, if can_be_in_queue was left as false, this function would always return false.
	if can_be_in_queue == false then
		can_be_in_queue = nil
	end

	--Return true if all of the following is true:
	--The definition exists
	--Either an entry in the queue exists and it can be in the queue, or there is no queue entry and it can't be in the queue.
	--This item is not something that would immediately be dug up anyways
	--This item isn't already cracked
	--This item is a node
	--This item doesn't originate from this mod.
	--This item can be destroyed
	--This item is visible
	return (def and queue[name] == can_be_in_queue and minetest.get_item_group(name, "dig_immediate") == 0 
		and minetest.get_item_group(name, "node_damage") == 0 and def.type == "node" and def.mod_origin ~= "node_damage" 
		and def.diggable and def.drawtype ~= "airlike")
end

--Once every mod has loaded and therefore every node has been registered...
minetest.register_on_mods_loaded(function()
	--For each node name in the queue...
	for name in pairs(queue) do
		--As long as the node is still valid
		if node_is_valid(name, true) then
			--Override the node to tell it which node to place when damaged.
			local def = {node_damaged_name = get_node_damage_name(name, 1)}
			minetest.override_item(name, def)

			--For each of the cracked stages...
			for i = 1, 3 do
				--Copy the base node's definition and remove information from the copy that can't be overridden.
				def = table.copy(minetest.registered_items[name])
				def.name = nil
				def.type = nil
				def.mod_origin = nil

				--Give it the not_in_creative_inventory and node_damage groups
				--The exact number of node_damage can be used to know how damaged a node is.
				def.groups = def.groups or {}
				def.groups.not_in_creative_inventory = 1
				def.groups.node_damage = i

				--If the node doesn't already define drops, make the cracked nodes only drop their fully repaired version.
				if not def.drop then
					def.drop = name
				end

				--If the damage stage is 1, repairing it gives the base node.
				if i == 1 then
					def.node_repaired_name = name
				--Otherwise, it gives the damage stage one less than this one.
				else
					def.node_repaired_name = get_node_damage_name(name, i - 1)
				end

				--If the damage stage isn't the highest, 3, damaging it gives the next stage of damage.
				if i ~= 3 then
					def.node_damaged_name = get_node_damage_name(name, i + 1)
				else
					--Stage 3 of damage doesn't place a new node when damage. They're just destroyed.
					def.node_damaged_name = nil
				end

				--If this node defines textures...
				if def.tiles then
					--For each tile...
					for k, tile in pairs(def.tiles) do
						--If the tile is just a string, overlay cracks onto the tile
						if type(tile) == "string" then
							def.tiles[k] = tile.."^node_damage_"..i..".png"
						--If there's a name field, overlay cracks onto the name
						elseif def.tiles[k].name then
							def.tiles[k].name = tile.name.."^node_damage_"..i..".png"
						--If there's an image field (deprecated), overlay cracks onto the image
						elseif def.tiles[k].image then
							def.tiles[k].image = tile.image.."^node_damage_"..i..".png"
						--Otherwise, relay an error message.
						else
							minetest.log("error: Could not overlay "..dump(tile))
						end
					end
				else
					--Otherwise, relay an error message.
					minetest.log(name.." has no tiles.")
					break
				end

				--Finally, override the cracked node's empty definition with the base node's altered definition.
				minetest.override_item(get_node_damage_name(name, i), def)
			end
		end
	end

	--This remembers if the player should be told to reload the world or not.
	local reload_msg = false

	--For each registered item...
	for name, def in pairs(minetest.registered_items) do
		--If there's a valid node that wasn't in the queue...
		if node_is_valid(name) then
			--Know that the reload message should be displayed.
			reload_msg = true

			--Remember the name of this newly added node.
			store:set_int(name, 1)
		end
	end

	--If a reload message should be displayed, show it.
	if reload_msg then
		minetest.log("New nodes have been added to the game. Please reload to enable them to use the Node Damage and Repair System.")
	end
end)



--A function to damage a given node, as long as that's possible.
--pos: The location of the node to damage.
--node: Optional; the node itself. It there's already data, you can pass it along to save time, but this function can grab the data itself.
--digger: Optional; A person who is attacking this node. If its destroyed, that person will pick it up.
--num: Optional, defaults to 1; The amount of times to damage this node. 3 will destroy any node_damage node.
function node_damage.damage(pos, node, digger, num)
	--If the node itself wasn't provided, grab it from the provided position
	if not node then
		node = minetest.get_node(pos)
	end

	--Get the node's definition
	local def = minetest.registered_items[node.name]

	--If the definition exists...
	if def then
		--If it defines a next stage of damage, swap to that next stage.
		if def.node_damaged_name and minetest.registered_items[def.node_damaged_name] then
			minetest.swap_node(pos, {name = def.node_damaged_name})
		--Otherwise, if it doesn't because it's in the last stage of damage, destroy the node.
		elseif def.groups.node_damage == 3 then
			--If a digger was provided, use node_dig to give the node to them.
			if digger then
				minetest.node_dig(pos, node, digger)
			--Otherwise, use the standard dig_node. This leaves the drops on the ground.
			else
				minetest.dig_node(pos, node)
			end
		end
	end

	--If num was provided and it was more than 1...
	if num and num > 1 then
		--Call damage again, but with 1 less num.
		node_damage.damage(pos, node, digger, num - 1)
	end
end

--The opposite of damage. Removes damage from a node, as long as its possible.
--pos: The location of the node to repair.
--node: Optional; the node itself. It there's already data, you can pass it along to save time, but this function can grab the data itself.
--num: Optional, defaults to 1; The amount of times to repair this node. 3 will repair any node that still exists.
function node_damage.repair(pos, node, num)
	--If the node itself wasn't provided, grab it from the provided position
	if not node then
		node = minetest.get_node(pos)
	end

	--Get the node's definition
	local def = minetest.registered_items[node.name]

	--If the definition exists and has the name of a less damaged node to switch to, swap the node.
	if def and def.node_repaired_name and minetest.registered_items[def.node_repaired_name] then
		minetest.swap_node(pos, {name = def.node_repaired_name})
	end

	--If num was provided and it was more than 1...
	if num and num > 1 then
		--Call repair again, but with 1 less num.
		node_damage.damage(pos, node, digger, num - 1)
	end
end



--Register a tool that can test both the damage and repair functions.
minetest.register_tool("node_damage:test_hammer", {
	description = "Node Damage Test Hammer",
	inventory_image = "node_damage_test_hammer.png",

	--When left-clicking, 
	on_use = function(itemstack, user, pointed_thing)
		--If the user is pointing at a node,
		if pointed_thing.type == "node" then
			--Get the position of that node
			local pos = pointed_thing.under

			--Damage it once.
			node_damage.damage(pos, nil, user)
		end
	end,

	--When right-clicking,
	on_place = function(itemstack, placer, pointed_thing)
		--If the user is pointing at a node,
		if pointed_thing.type == "node" then
			--Get the position of that node
			local pos = pointed_thing.under

			--Repair it once.
			node_damage.repair(pos)
		end
	end
})



--If the tnt mod is being used...
if tnt then
	--Create a function that, after blasing a position, cracks nearby nodes.
	local function on_blast(pos, intensity)
		--Blast the position with a 3 node radius.
		tnt.boom(pos, {radius = minetest.settings:get("tnt_radius") or 3})

		--Cracking radius is set to a minimum of 5, but can be bigger if the explosion is more intense.
		local r = 5 * math.max(1, intensity)

		--In an 11x11x11 cube...
		for a = -r, r do
			for b = -r, r do
				for c = -r, r do
					--Get the current pos of the node to damage
					local npos = vector.add(pos, {x=a, y=b, z=c})
					--Get the distance between the current node and the center of the blast
					local dist = vector.distance(pos, npos)
					--Get the number of times to crack this node. Its random,
					--but the maximum increases when its closer to the center of the blast.
					local num = math.random(0, math.ceil(r / math.max(1, dist)))

					--If the distance of this node is within the radius of 5 (to create more of a spherical shape than a cube)
					--And the randomly selected num wasn't 0...
					if dist <= r and num > 0 then
						--Damage this particular node num times.
						node_damage.damage(npos, nil, nil, num)
					end
				end
			end
		end
	end

	--Override tnt blocks to use the above function when exploded.
	minetest.override_item("tnt:tnt", {
		on_blast = function(pos, intensity)
			minetest.after(0.1, on_blast, pos, intensity)
		end
	})

	--Override burning tnt blocks to use the above function once the timer runs out.
	minetest.override_item("tnt:tnt_burning", {
		on_timer = function(pos, elapsed)
			on_blast(pos, 1)
		end
	})
end