-- Nodes that function as cauldrons
local CAULDRONS = {}

-- How many nodes downwards a droplet is able to drop from a stalactite
-- before the droplet evaporates.
local DROP_DOWN_REACH = 50

-- The number of seconds it takes for a dripstone node to grow 1 unit
-- (NOTE: Not one node size! One unit, which quadratically increases
-- per node size.)
local GROWTH_FACTOR = 3

-- This mod's name.
local MODNAME = minetest.get_current_modname()

-- The number of samples that each ABM should execute.
-- Make sure this is a whole number and less than speed_factor.
local SAMPLES_PER_INTERVAL = 30

-- Nodes that provide droplets
local SOURCES = {}

-- Factor deciding this mod's relative speed.
-- Set this value to 1 if you wish to debug and let the dripstone
-- change rapidly.
-- Rule of thumb: with a setting of 60, it takes a lava farm about 30
-- minutes to fill a cauldron with lava.
local SPEED_FACTOR = 60

-- Nodes that allow a droplet to trickle down if it is directly below a
	-- node that passes down that droplet.
local TRICKLERS = {}

-- Names of the various dripstone widths
local WIDTH_NAMES = {
	"spike", "tiny", "small", "medium", "great", "large", "huge", "block",
}

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

-- Internal table that lets us define functions without directly exposing them.
local internal = {}

-- Capitalize a string
function internal.capitalize(str)
	return (str:gsub("^%l", string.upper))
end

function internal.drawtype_of_size(size)
	if size >= 8 then
		return "normal"
	else
		return "nodebox"
	end
end

function internal.hit_with_droplet(pos, node, droplet, spikename)
	local m = CAULDRONS[droplet] or {}

	if m[node.name] == nil then
		-- Not a cauldron! Therefore we place a spike on top.
		pos = vector.offset(pos, 0, 1, 0)
		node = minetest.get_node(pos)
		node.name = spikename
		minetest.set_node(pos, node)
	else
		node.name = m[node.name]
		minetest.set_node(pos, node)
	end
end

-- Determine whether this mod considers a node an air node.
function internal.is_air(nodename)
	return (nodename == "air") or (minetest.get_item_group(nodename, "air") ~= 0)
end

-- Create a node box for any given dripstone size.
-- Size 8 is a normal block size
function internal.nodebox_of_size(size)
	if size >= 8 then
		return nil
	else
		return {
			type = "fixed",
			fixed = {
				{ - size / 16, -0.5, - size / 16, size / 16, 0.5, size / 16 },
			},
		}
	end
end

function internal.register_absorb_abm(droplet, oldnodename, newnodename)
	minetest.register_abm({
		nodenames = { oldnodename },
		interval = SPEED_FACTOR / SAMPLES_PER_INTERVAL,
		chance = SAMPLES_PER_INTERVAL,
		catch_up = true,
		action = function(pos, node)
			local pos_above = vector.offset(pos, 0, 1, 0)
			local node_above = minetest.get_node(pos_above)

			for _, source in pairs(SOURCES[droplet] or {}) do
				if node_above.name == source then
					node.name = newnodename
					minetest.set_node(pos, node)
					return
				end
			end
		end
	})
end

function internal.register_dripstone_craft(newnodename, oldnodename, spikename)
	minetest.register_craft({
		output = newnodename,
		recipe = {
			{ spikename, spikename  , spikename },
			{ spikename, oldnodename, spikename },
			{ spikename, spikename  , spikename },
		}
	})
end

function internal.register_dripstone_flavor(flavor, def)
	-- Guaranteed values
	local drop = def.drop or internal.size_to_name(flavor, 1)
	local on_droplet_receive = def.on_droplet_receive or {}
	local trickle_speed = def.trickle_speed or 1

	-- Potentially nil, might need to be checked before assumed safe
	local dry_up = def.grow_to
	local sounds = def.sounds
	local tiles = def.tiles
	local trickl = def.trickle_down

	-- Register nodes
	for width = 1, 8, 1 do
		internal.register_dripstone_node(flavor, width, tiles, sounds, drop)
	end

	-- Register upgrade crafting recipes
	for width = 1, 6, 1 do
		internal.register_dripstone_craft(
			internal.size_to_name(flavor, width + 1),
			internal.size_to_name(flavor, width),
			internal.size_to_description(flavor, 1)
		)
	end

	-- Allow dripstone nodes to trickle down droplets
	for droplet, new_flavor in pairs(on_droplet_receive) do
		for width = 1, 8, 1 do
			internal.register_trickler(
				droplet,
				internal.size_to_name(flavor, width),
				internal.size_to_name(new_flavor, width)
			)
		end
	end

	-- Makes dripstone stalagmite spikes delete droplets.
	-- Without this, stalactites remain very thick and short while
	-- stalagmites become absurdly long and thin.
	-- A watered stalagmite can't accept a water droplet and the stalagmite
	-- therefore grows one per droplet. To mitigate this, a watered spike
	-- can still act as a water droplet cauldron without changing.
	-- This way, no new droplets are passed on if the stalagmite is already
	-- full, and the structure simply waits for a dripstone node to grow.
	-- This behaviour is designed to be easy to override. (For example: if
	-- you want a HEAVY watered dripstone type that holds 2 droplets.)
	if trickl then
		internal.register_droplet_catcher(
			trickl,
			internal.size_to_name(flavor, 1),
			internal.size_to_name(flavor, 1)
		)
	end

	-- Allow spike stalagmites to catch droplets.
	-- This feature can override the former safeguard.
	for droplet, new_flavor in pairs(on_droplet_receive) do
		internal.register_droplet_catcher(
			droplet,
			internal.size_to_name(flavor, 1),
			internal.size_to_name(new_flavor, 1)
		)
	end

	-- Register ABM to grow when possible.
	if dry_up then
		for width = 1, 6, 1 do
			internal.register_grow_abm(
				internal.size_to_name(flavor, width),
				internal.size_to_name(dry_up, width + 1),
				width
			)
		end
	end

	-- Register ABM to grow when possible
	if trickl and dry_up then
		for width = 1, 8, 1 do
			internal.register_trickle_down_abm(
				trickl,
				width,
				internal.size_to_name(flavor, width),
				internal.size_to_name(dry_up, width),
				dry_up,
				trickle_speed
			)
		end
	end

	-- Register ABM to absorb liquids from above
	for droplet, new_flavor in pairs(on_droplet_receive) do
		internal.register_absorb_abm(
			droplet,
			internal.size_to_name(flavor, 8),
			internal.size_to_name(new_flavor, 8)
		)
	end

	-- Register ABM to drop down droplets from a stalactite spike
	if dry_up and trickl then
		internal.register_drop_down_abm(
			trickl,
			internal.size_to_name(flavor, 1),
			internal.size_to_name(dry_up, 1),
			trickle_speed
		)
	end
end

function internal.register_dripstone_node(flavor, size, tiles, sounds, drop)
	minetest.register_node(internal.size_to_name(flavor, size), {
		description = internal.size_to_description(flavor, size),
		tiles = tiles,
		groups = {
			pickaxey = 2,
			material_stone = 1,
			fall_damage_add_percent = math.max(4 - size, 0) / 4 * 100
		},
		is_ground_content = true,
		drop = {
			max_items = math.floor((size + 1) / 2),
			items = {
				{
					rarity = 1,
					items = { drop },
				},
				{
					rarity = 2,
					items = { drop },
				},
				{
					rarity = 4,
					items = { drop },
				},
				{
					rarity = 4,
					items = { drop },
				},
			}
		},
		sounds = sounds,
		drawtype = internal.drawtype_of_size(size),
		paramtype = "light",
		sunlight_propagates = size < 8,
		node_box = internal.nodebox_of_size(size),
		_mcl_hardness = 1.0 + size / 8,
		_mcl_blast_resistance = 1 + size / 2,
		_mcl_silk_touch_drop = true,
	})
end

function internal.register_drop_down_abm(droplet, spikename, dryspikename, trickle_speed)
	minetest.register_abm({
		nodenames = { spikename },
		interval = trickle_speed * SPEED_FACTOR / SAMPLES_PER_INTERVAL,
		chance = SAMPLES_PER_INTERVAL,
		catch_up = true,
		action = function(pos, node)
			local pos_below = vector.offset(pos, 0, -1, 0)
			local node_below = minetest.get_node(pos_below)

			if not internal.is_air(node_below.name) then
				-- Node below is not air! Unable to drop a droplet down.
				return
			end

			for dy = 2, DROP_DOWN_REACH, 1 do
				pos_below = vector.offset(pos, 0, -dy, 0)
				node_below = minetest.get_node(pos_below)

				if not internal.is_air(node_below.name) then
					-- Node is not air! If it is a cauldron, update the node.
					internal.hit_with_droplet(
						pos_below,
						node_below,
						droplet,
						dryspikename
					)
					break
				end
			end

			node.name = dryspikename
			minetest.set_node(pos, node)
		end
	})
end

-- Register a new droplet type that can be absorbed and passed on by dripstone.
function internal.register_droplet(droplet)
	if CAULDRONS[droplet] == nil then
		CAULDRONS[droplet] = {}
	end
	if SOURCES[droplet] == nil then
		SOURCES[droplet] = {}
	end
	if TRICKLERS[droplet] == nil then
		TRICKLERS[droplet] = {}
	end
end

-- Add a droplet catcher, which is a node that allows a stalactite spike to
-- change the name using a droplet.
function internal.register_droplet_catcher(droplet, oldnodename, newnodename)
	if CAULDRONS[droplet] == nil then
		internal.uninitialized_droplet_error(droplet)
	end

	CAULDRONS[droplet][oldnodename] = newnodename
end

function internal.register_droplet_source(droplet, nodename)
	if SOURCES[droplet] == nil then
		internal.uninitialized_droplet_error(droplet)
	end
	table.insert(SOURCES[droplet], nodename)

	-- If the node can emit an infinite number of droplets,
	-- it can also absorb an infinite number of droplets.
	internal.register_droplet_catcher(droplet, nodename, nodename)
end

function internal.register_grow_abm(oldnodename, newnodename, width)
	minetest.register_abm({
		nodenames = { oldnodename },
		-- 2(w + 1) * 2(w + 1) - 2w * 2w = 8w + 4
		interval = (8 * width + 4) * SPEED_FACTOR * GROWTH_FACTOR / SAMPLES_PER_INTERVAL,
		chance = SAMPLES_PER_INTERVAL,
		catch_up = true,
		action = function(pos, node)
			node.name = newnodename
			minetest.set_node(pos, node)
		end
	})
end

function internal.register_trickle_down_abm(droplet, width, old_source, new_source, dry_up, trickle_speed)
	minetest.register_abm({
		nodenames = { old_source },
		interval = trickle_speed * SPEED_FACTOR / SAMPLES_PER_INTERVAL,
		chance = SAMPLES_PER_INTERVAL,
		catch_up = true,
		action = function(pos, node)
			local pos_below = vector.offset(pos, 0, -1, 0)
			local node_below = minetest.get_node(pos_below)

			local m = TRICKLERS[droplet] or {}

			if m[node_below.name] ~= nil then
				-- Trickler found below!
				node_below.name = m[node_below.name]
			elseif width > 1 and internal.is_air(node_below.name) then
				-- Air node found below a non-spike, turn it into a spike.
				node_below.name = internal.size_to_name(dry_up, 1)
			else
				return -- Prevent droplet from leaking away
			end

			node.name = new_source
			minetest.set_node(pos_below, node_below)
			minetest.set_node(pos, node)
		end
	})
end

-- Add a droplet trickler, which is a dripstone node that allows a droplet to
-- be trickled down from the node directly above it.
-- Running this function overrides previous values.
function internal.register_trickler(droplet, oldnodename, newnodename)
	if TRICKLERS[droplet] == nil then
		internal.uninitialized_droplet_error(droplet)
	end

	TRICKLERS[droplet][oldnodename] = newnodename
end

function internal.size_to_description(flavor, size)
	local width_name = WIDTH_NAMES[size]

	if size == 1 or size == 8 then
		return internal.capitalize(flavor) .. " dripstone " .. width_name
	else
		return internal.capitalize(width_name) .. " " .. flavor .. " dripstone"
	end
end

function internal.size_to_name(flavor, size)
	local namespace = MODNAME .. ":"
	local width_name = WIDTH_NAMES[size]

	if size == 1 or size == 8 then
		return namespace .. flavor .. "_dripstone_" .. width_name
	else
		return namespace .. width_name .. "_" .. flavor .. "_dripstone"
	end
end

function internal.uninitialized_droplet_error(droplet)
	error(
		"Droplet " .. droplet .. " has not been initialized yet!"
	)
end

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
---------------------------     PUBLIC API     --------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

dripstone = {
	-- DEPRECATED: will be removed in next major version
	add_droplet_catcher = internal.register_droplet_catcher,

	-- DEPRECATED: will be removed in next major version
	add_droplet_source = internal.register_droplet_source,

	-- Register a node that can catch a droplet from a dripstone stalactite.
	register_catcher = internal.register_droplet_catcher,

	-- Register a new dripstone type.
	register_dripstone = internal.register_dripstone_flavor,

	-- Register a new droplet type that can be absorbed and passed on by dripstone.
	register_droplet = internal.register_droplet,

	-- Register a source node that can provide droplets to dripstone blocks.
	register_source = internal.register_droplet_source,

	-- Get a dripstone's node name based on its flavor and size.
	size_to_name = internal.size_to_name,
}