VoxeLibre/mods/ITEMS/REDSTONE/mcl_comparators/init.lua

local S = minetest.get_translator(minetest.get_current_modname())

-- Functions that get the input/output rules of the comparator

local function comparator_get_output_rules(node)
	local rules = {{x = -1, y = 0, z = 0, spread=true}}
	for i = 0, node.param2 do
		rules = mesecon.rotate_rules_left(rules)
	end
	return rules
end


local function comparator_get_input_rules(node)
	local rules = {
		-- we rely on this order in update_self below
		{x = 1, y = 0, z =  0},  -- back
		{x = 0, y = 0, z = -1},  -- side
		{x = 0, y = 0, z =  1},  -- side
	}
	for i = 0, node.param2 do
		rules = mesecon.rotate_rules_left(rules)
	end
	return rules
end


-- Functions that are called after the delay time

local function comparator_turnon(params)
	local rules = comparator_get_output_rules(params.node)
	mesecon.receptor_on(params.pos, rules)
end


local function comparator_turnoff(params)
	local rules = comparator_get_output_rules(params.node)
	mesecon.receptor_off(params.pos, rules)
end


-- Functions that set the correct node type an schedule a turnon/off

local function comparator_activate(pos, node)
	local def = minetest.registered_nodes[node.name]
	minetest.swap_node(pos, { name = def.comparator_onstate, param2 = node.param2 })
	minetest.after(0.1, comparator_turnon , {pos = pos, node = node})
end


local function comparator_deactivate(pos, node)
	local def = minetest.registered_nodes[node.name]
	minetest.swap_node(pos, { name = def.comparator_offstate, param2 = node.param2 })
	minetest.after(0.1, comparator_turnoff, {pos = pos, node = node})
end


-- weather pos has an inventory that contains at least one item
local function container_inventory_nonempty(pos)
	local invnode = minetest.get_node(pos)
	local invnodedef = minetest.registered_nodes[invnode.name]
	-- Ignore stale nodes
	if not invnodedef then return false end

	-- Only accept containers. When a container is dug, it's inventory
	-- seems to stay. and we don't want to accept the inventory of an air
	-- block
	if not invnodedef.groups.container then return false end

	local inv = minetest.get_inventory({type="node", pos=pos})
	if not inv then return false end

	for listname, _ in pairs(inv:get_lists()) do
		if not inv:is_empty(listname) then return true end
	end

	return false
end

-- weather pos has an constant signal output for the comparator
local function static_signal_output(pos)
	local node = minetest.get_node(pos)
	local g = minetest.get_item_group(node.name, "comparator_signal")
	return g > 0
end

-- whether the comparator should be on according to its inputs
local function comparator_desired_on(pos, node)
	local my_input_rules = comparator_get_input_rules(node);
	local back_rule = my_input_rules[1]
	local state
	if back_rule then
		local back_pos = vector.add(pos, back_rule)
		state = mesecon.is_power_on(back_pos) or container_inventory_nonempty(back_pos) or static_signal_output(back_pos)
	end

	-- if back input if off, we don't need to check side inputs
	if not state then return false end

	-- without power levels, side inputs have no influence on output in compare
	-- mode
	local mode = minetest.registered_nodes[node.name].comparator_mode
	if mode == "comp" then return state end

	-- subtract mode, subtract max(side_inputs) from back input
	local side_state = false
	for ri = 2,3 do
		if my_input_rules[ri] then
			side_state = mesecon.is_power_on(vector.add(pos, my_input_rules[ri]))
		end
		if side_state then break end
	end
	-- state is known to be true
	return not side_state
end


-- update comparator state, if needed
local function update_self(pos, node)
	node = node or minetest.get_node(pos)
	local old_state = mesecon.is_receptor_on(node.name)
	local new_state = comparator_desired_on(pos, node)
	if new_state ~= old_state then
		if new_state then
			comparator_activate(pos, node)
		else
			comparator_deactivate(pos, node)
		end
	end
end


-- compute tile depending on state and mode
local function get_tiles(state, mode)
	local top = "mcl_comparators_"..state..".png^"..
		"mcl_comparators_"..mode..".png"
	local sides = "mcl_comparators_sides_"..state..".png^"..
		"mcl_comparators_sides_"..mode..".png"
	local ends = "mcl_comparators_ends_"..state..".png^"..
		"mcl_comparators_ends_"..mode..".png"
	return {
		top, "mcl_stairs_stone_slab_top.png",
		sides, sides.."^[transformFX",
		ends, ends,
	}
end

-- Given one mode, get the other mode
local function flipmode(mode)
	if mode == "comp" then    return "sub"
	elseif mode == "sub" then return "comp"
	end
end

local function make_rightclick_handler(state, mode)
	local newnodename =
		"mcl_comparators:comparator_"..state.."_"..flipmode(mode)
	return function (pos, node, clicker)
		local protname = clicker:get_player_name()
		if minetest.is_protected(pos, protname) then
			minetest.record_protection_violation(pos, protname)
			return
		end
		minetest.swap_node(pos, {name = newnodename, param2 = node.param2 })
	end
end


-- Register the 2 (states) x 2 (modes) comparators

local icon = "mcl_comparators_item.png"

local node_boxes = {
	comp = {
		{ -8/16, -8/16, -8/16,
		   8/16, -6/16,  8/16 },	-- the main slab
		{ -1/16, -6/16,  6/16,
		   1/16, -4/16,  4/16 },	-- front torch
		{ -4/16, -6/16, -5/16,
		  -2/16, -1/16, -3/16 },	-- left back torch
		{  2/16, -6/16, -5/16,
		   4/16, -1/16, -3/16 },	-- right back torch
	},
	sub = {
		{ -8/16, -8/16, -8/16,
		   8/16, -6/16,  8/16 },	-- the main slab
		{ -1/16, -6/16,  6/16,
		   1/16, -3/16,  4/16 },	-- front torch (active)
		{ -4/16, -6/16, -5/16,
		  -2/16, -1/16, -3/16 },	-- left back torch
		{  2/16, -6/16, -5/16,
		   4/16, -1/16, -3/16 },	-- right back torch
	},
}

local collision_box = {
	type = "fixed",
	fixed = { -8/16, -8/16, -8/16, 8/16, -6/16, 8/16 },
}

local state_strs = {
	[ mesecon.state.on  ] = "on",
	[ mesecon.state.off ] = "off",
}

local groups = {
	dig_immediate = 3,
	dig_by_water  = 1,
	destroy_by_lava_flow = 1,
	dig_by_piston = 1,
	attached_node = 1,
}

local on_rotate
if minetest.get_modpath("screwdriver") then
	on_rotate = screwdriver.disallow
end

for _, mode in pairs{"comp", "sub"} do
	for _, state in pairs{mesecon.state.on, mesecon.state.off} do
		local state_str = state_strs[state]
		local nodename =
			"mcl_comparators:comparator_"..state_str.."_"..mode

		-- Help
		local longdesc, usagehelp, use_help
		if state_str == "off" and mode == "comp" then
			longdesc = S("Redstone comparators are multi-purpose redstone components.").."\n"..
			S("They can transmit a redstone signal, detect whether a block contains any items and compare multiple signals.")

			usagehelp = S("A redstone comparator has 1 main input, 2 side inputs and 1 output. The output is in arrow direction, the main input is in the opposite direction. The other 2 sides are the side inputs.").."\n"..
				S("The main input can powered in 2 ways: First, it can be powered directly by redstone power like any other component. Second, it is powered if, and only if a container (like a chest) is placed in front of it and the container contains at least one item.").."\n"..
				S("The side inputs are only powered by normal redstone power. The redstone comparator can operate in two modes: Transmission mode and subtraction mode. It starts in transmission mode and the mode can be changed by using the block.").."\n\n"..
				S("Transmission mode:\nThe front torch is unlit and lowered. The output is powered if, and only if the main input is powered. The two side inputs are ignored.").."\n"..
				S("Subtraction mode:\nThe front torch is lit. The output is powered if, and only if the main input is powered and none of the side inputs is powered.")
		else
			use_help = false
		end

		local nodedef = {
			description = S("Redstone Comparator"),
			inventory_image = icon,
			wield_image = icon,
			_doc_items_create_entry = use_help,
			_doc_items_longdesc = longdesc,
			_doc_items_usagehelp = usagehelp,
			drawtype = "nodebox",
			tiles = get_tiles(state_str, mode),
			use_texture_alpha = minetest.features.use_texture_alpha_string_modes and "opaque" or false,
			--wield_image = "mcl_comparators_off.png",
			walkable = true,
			selection_box = collision_box,
			collision_box = collision_box,
			node_box = {
				type = "fixed",
				fixed = node_boxes[mode],
			},
			groups = groups,
			paramtype = "light",
			paramtype2 = "facedir",
			sunlight_propagates = false,
			is_ground_content = false,
			drop = "mcl_comparators:comparator_off_comp",
			on_construct = update_self,
			on_rightclick =
				make_rightclick_handler(state_str, mode),
			comparator_mode = mode,
			comparator_onstate = "mcl_comparators:comparator_on_"..mode,
			comparator_offstate = "mcl_comparators:comparator_off_"..mode,
			sounds = mcl_sounds.node_sound_stone_defaults(),
			mesecons = {
				receptor = {
					state = state,
					rules = comparator_get_output_rules,
				},
				effector = {
					rules = comparator_get_input_rules,
					action_change = update_self,
				}
			},
			on_rotate = on_rotate,
		}

		if mode == "comp" and state == mesecon.state.off then
			-- This is the prototype
			nodedef._doc_items_create_entry = true
		else
			nodedef.groups = table.copy(nodedef.groups)
			nodedef.groups.not_in_creative_inventory = 1
			--local extra_desc = {}
			if mode == "sub" or state == mesecon.state.on then
				nodedef.inventory_image = nil
			end
			local desc = nodedef.description
			if mode ~= "sub" and state == mesecon.state.on then
				desc = S("Redstone Comparator (Powered)")
			elseif mode == "sub" and state ~= mesecon.state.on then
				desc = S("Redstone Comparator (Subtract)")
			elseif mode == "sub" and state == mesecon.state.on then
				desc = S("Redstone Comparator (Subtract, Powered)")
			end
			nodedef.description = desc
		end

		minetest.register_node(nodename, nodedef)
		mcl_wip.register_wip_item(nodename)
	end
end

-- Register recipies
local rstorch = "mesecons_torch:mesecon_torch_on"
local quartz  = "mcl_nether:quartz"
local stone   = "mcl_core:stone"

minetest.register_craft({
	output = "mcl_comparators:comparator_off_comp",
	recipe = {
		{ "",      rstorch, ""      },
		{ rstorch, quartz,  rstorch },
		{ stone,   stone,   stone   },
	}
})

-- Register active block handlers
minetest.register_abm({
	label = "Comparator signal input check (comparator is off)",
	nodenames = {
		"mcl_comparators:comparator_off_comp",
		"mcl_comparators:comparator_off_sub",
	},
	neighbors = {"group:container", "group:comparator_signal"},
	interval = 1,
	chance = 1,
	action = update_self,
})

minetest.register_abm({
	label = "Comparator signal input check (comparator is on)",
	nodenames = {
		"mcl_comparators:comparator_on_comp",
		"mcl_comparators:comparator_on_sub",
	},
	-- needs to run regardless of neighbors to make sure we detect when a
	-- container is dug
	interval = 1,
	chance = 1,
	action = update_self,
})


-- Add entry aliases for the Help
if minetest.get_modpath("doc") then
	doc.add_entry_alias("nodes", "mcl_comparators:comparator_off_comp",
				"nodes", "mcl_comparators:comparator_off_sub")
	doc.add_entry_alias("nodes", "mcl_comparators:comparator_off_comp",
				"nodes", "mcl_comparators:comparator_on_comp")
	doc.add_entry_alias("nodes", "mcl_comparators:comparator_off_comp",
				"nodes", "mcl_comparators:comparator_on_sub")
end