Optimize the mod code

This also improves formatting to comply with Minetest's
Lua code style guidelines.

init.lua

@@ -3,62 +3,52 @@
 -- Copyright © 2014-2020 4aiman, Hugo Locurcio and contributors - MIT License
 -- See `LICENSE.md` included in the source distribution for details.
 
-local hp_bar = {
-	physical = false,
-	collisionbox = {x = 0, y = 0, z = 0},
+if minetest.settings:get_bool("health_bars") == false or
+		not minetest.settings:get_bool("enable_damage")
+then return end
+
+minetest.register_entity("gauges:hp_bar", {
 	visual = "sprite",
-	textures = {"20.png"}, -- The texture is changed later in the code
-	visual_size = {x = 1.5, y = 0.09375, z = 1.5}, -- Y value is (1 / 16) * 1.5
-	wielder = nil,
-}
+	visual_size = {x=1, y=1/16, z = 1},
+	-- The texture is changed later in the code
+	textures = {"blank.png"},
+	collisionbox = {0},
+	physical = false,
 
-function vector.sqdist(a, b)
-	local dx = a.x - b.x
-	local dy = a.y - b.y
-	local dz = a.z - b.z
-	return dx * dx + dy * dy + dz * dz
-end
+	on_step = function(self)
+		local player = self.wielder
 
-function hp_bar:on_step(dtime)
-	local wielder = self.wielder and minetest.get_player_by_name(self.wielder)
-
-	if
-		wielder == nil or
-		vector.sqdist(wielder:get_pos(), self.object:get_pos()) > 3
+		if not player or
+				not minetest.is_player(player) or
+				vector.distance(player:get_pos(), self.object:get_pos()) > 3
 		then
 			self.object:remove()
 			return
 		end
 
-	local hp = wielder:get_hp()
-	local breath = wielder:get_breath()
+		local hp = player:get_hp() <= 20 and player:get_hp() or 20
+		local breath = player:get_breath() <= 10 and player:get_breath() or 11
 
+		if self.hp ~= hp or self.breath ~= breath then
 			self.object:set_properties({
 				textures = {
-			"health_" .. tostring(hp) .. ".png^breath_" .. tostring(breath) .. ".png",
-		},
+					"health_"..tostring(hp)..".png^"..
+					"breath_"..tostring(breath)..".png"
+				}
 			})
-end
-
-minetest.register_entity("gauges:hp_bar", hp_bar)
-
-local function add_HP_gauge(name)
-	local player = minetest.get_player_by_name(name)
-	local pos = player:get_pos()
-	local ent = minetest.add_entity(pos, "gauges:hp_bar")
-
-	if ent ~= nil then
-		ent:set_attach(player, "", {x = 0, y = 19, z = 0}, {x = 0, y = 0, z = 0})
-		ent = ent:get_luaentity()
-		ent.wielder = player:get_player_name()
+			self.hp = hp
+			self.breath = breath
 		end
 	end
+})
+
+local function add_gauge(player)
+	local entity = minetest.add_entity(player:get_pos(), "gauges:hp_bar")
+
+	entity:set_attach(player, "", {x=0, y=19, z=0}, {x=0, y=0, z=0})
+	entity:get_luaentity().wielder = player
+end
 
-if
-	minetest.settings:get_bool("enable_damage") and
-	minetest.settings:get_bool("health_bars") ~= false
-then
 minetest.register_on_joinplayer(function(player)
-		minetest.after(1, add_HP_gauge, player:get_player_name())
+	minetest.after(1, add_gauge, player)
 end)
-end