Add command block:

* not obtainable legitimately in Survival mode
* found in Creative inventory or using /giveme mesecons_commandblock:commandblock_off
* glows slightly when turned on
* runs a command in the context of the targeted player
* player can be targeted by name, or using the special forms (@nearest, @farthest, @random)
* when powered, runs its command with its parameters
* right click to bring up the configuration screen
* diggable and modifiable only by its owner, the person who placed it

mesecons_commandblock/depends.txt

@@ -0,0 +1 @@
+mesecons

mesecons_commandblock/init.lua

@@ -0,0 +1,157 @@
+local initialize_data = function(meta, player, command, param)
+	meta:set_string("formspec",
+		"invsize[9,6;]" ..
+		"field[1,1;7.5,1;player;Player;" .. player .. "]" ..
+		"button[1.3,2;2,1;nearest;Nearest]" ..
+		"button[3.3,2;2,1;farthest;Farthest]" ..
+		"button[5.3,2;2,1;random;Random]" ..
+		"field[1,4;2,1;command;Command;" .. command .. "]" ..
+		"field[3,4;5.5,1;param;Parameter;" .. param .. "]" ..
+		"button_exit[3.3,5;2,1;submit;Submit]")
+	local owner = meta:get_string("owner")
+	if owner == "" then
+		owner = "not owned"
+	else
+		owner = "owned by " .. owner
+	end
+	meta:set_string("infotext", "Command Block\n" ..
+		"(" .. owner .. ")\n" ..
+		"Command: /" .. command .. " " .. param)
+end
+
+local construct = function(pos)
+	local meta = minetest.env:get_meta(pos)
+
+	meta:set_string("player", "@nearest")
+	meta:set_string("command", "time")
+	meta:set_string("param", "7000")
+
+	meta:set_string("owner", "")
+
+	initialize_data(meta, "@nearest", "time", "7000")
+end
+
+local after_place = function(pos, placer)
+	if placer then
+		local meta = minetest.env:get_meta(pos)
+		meta:set_string("owner", placer:get_player_name())
+		initialize_data(meta, "@nearest", "time", "7000")
+	end
+end
+
+local receive_fields = function(pos, formname, fields, sender)
+	local meta = minetest.env:get_meta(pos)
+	if fields.nearest then
+		initialize_data(meta, "@nearest", fields.command, fields.param)
+	elseif fields.farthest then
+		initialize_data(meta, "@farthest", fields.command, fields.param)
+	elseif fields.random then
+		initialize_data(meta, "@random", fields.command, fields.param)
+	else --fields.submit or pressed enter
+		meta:set_string("player", fields.player)
+		meta:set_string("command", fields.command)
+		meta:set_string("param", fields.param)
+
+		initialize_data(meta, fields.player, fields.command, fields.param)
+	end
+end
+
+local resolve_player = function(name, pos)
+	local get_distance = function(pos1, pos2)
+		return math.sqrt((pos1.x - pos2.x) ^ 2 + (pos1.y - pos2.y) ^ 2 + (pos1.z - pos2.z) ^ 2)
+	end
+
+	if name == "@nearest" then
+		local min_distance = math.huge
+		for index, player in ipairs(minetest.get_connected_players()) do
+			local distance = get_distance(pos, player:getpos())
+			if distance < min_distance then
+				min_distance = distance
+				name = player:get_player_name()
+			end
+		end
+	elseif name == "@farthest" then
+		local max_distance = -1
+		for index, player in ipairs(minetest.get_connected_players()) do
+			local distance = get_distance(pos, player:getpos())
+			if distance > max_distance then
+				max_distance = distance
+				name = player:get_player_name()
+			end
+		end
+	elseif name == "@random" then
+		local players = minetest.get_connected_players()
+		local player = players[math.random(#players)]
+		name = player:get_player_name()
+	end
+	return name
+end
+
+minetest.register_node("mesecons_commandblock:commandblock_off", {
+	description = "Command Block",
+	tiles = {"jeija_commandblock_off.png"},
+	inventory_image = minetest.inventorycube("jeija_commandblock_off.png"),
+	groups = {cracky=2, mesecon_effector_off=1, mesecon=2},
+	on_construct = construct,
+	after_place_node = after_place,
+	on_receive_fields = receive_fields,
+	can_dig = function(pos,player)
+		local owner = minetest.env:get_meta(pos):get_string("owner")
+		return owner == "" or owner == player:get_player_name()
+	end,
+})
+
+minetest.register_node("mesecons_commandblock:commandblock_on", {
+	tiles = {"jeija_commandblock_on.png"},
+	groups = {cracky=2, mesecon_effector_on=1, mesecon=2, not_in_creative_inventory=1},
+	light_source = 10,
+	drop = "mesecons_commandblock:commandblock_off",
+	on_construct = construct,
+	after_place_node = after_place,
+	on_receive_fields = receive_fields,
+	can_dig = function(pos,player)
+		local owner = minetest.env:get_meta(pos):get_string("owner")
+		return owner == "" or owner == player:get_player_name()
+	end,
+})
+
+mesecon:register_effector("mesecons_commandblock:commandblock_on", "mesecons_commandblock:commandblock_off")
+
+local swap_node = function(pos, name)
+	local node = minetest.env:get_node(pos)
+	local data = minetest.env:get_meta(pos):to_table()
+	node.name = name
+	minetest.env:add_node(pos, node)
+	minetest.env:get_meta(pos):from_table(data)
+end
+
+mesecon:register_on_signal_on(function(pos, node)
+	if node.name ~= "mesecons_commandblock:commandblock_off" then
+		return
+	end
+
+	swap_node(pos, "mesecons_commandblock:commandblock_on")
+
+	local meta = minetest.env:get_meta(pos)
+	local command = minetest.chatcommands[meta:get_string("command")]
+	if command == nil then
+		return
+	end
+	local owner = meta:get_string("owner")
+	if owner == "" then
+		return
+	end
+	local has_privs, missing_privs = minetest.check_player_privs(owner, command.privs)
+	if not has_privs then
+		minetest.chat_send_player(owner, "You don't have permission to run this command (missing privileges: "..table.concat(missing_privs, ", ")..")")
+		return
+	end
+	local player = resolve_player(meta:get_string("player"), pos)
+	command.func(player, meta:get_string("param"))
+end)
+
+mesecon:register_on_signal_off(function(pos, node)
+	if node.name == "mesecons_commandblock:commandblock_on" then
+		swap_node(pos, "mesecons_commandblock:commandblock_off")
+	end
+end)