MTSM/mods/climates/lib/skybox_merger.lua

local default_sky = {
	sky_data = {
		base_color = nil,
		type = "regular",
		textures = nil,
		clouds = true,
		sky_color = {
			day_sky = "#8cbafa",
			day_horizon = "#9bc1f0",
			dawn_sky = "#b4bafa",
			dawn_horizon = "#bac1f0",
			night_sky = "#006aff",
			night_horizon = "#4090ff",
			indoors = "#646464",
			fog_tint_type = "default"
		}
	},
	cloud_data = {
		density = 0.4,
		color = "#fff0f0e5",
		ambient = "#000000",
		height = 120,
		thickness = 16,
		speed = {x=0, z=-2}
	},
	sun_data = {
		visible = true,
		texture = "sun.png",
		tonemap = "sun_tonemap.png",
		sunrise = "sunrisebg.png",
		sunrise_visible = true,
		scale = 1
	},
	moon_data = {
		visible = true,
		texture = "moon.png",
		tonemap = "moon_tonemap.png",
		scale = 1
	},
	star_data = {
		visible = true,
		count = 1000,
		star_color = "#ebebff69",
		scale = 1
	}
}

local skybox = {}
local layers = {}

-- from https://stackoverflow.com/a/29133654
-- merges two tables together
-- if in conflict, b will override values of a
local function merge_tables(a, b)
	if type(a) == "table" and type(b) == "table" then
		for k,v in pairs(b) do
			if type(v)=="table" and type(a[k] or false)=="table" then
				merge_tables(a[k],v)
			else a[k]=v end
		end
	end
	return a
end

local function set_skybox(playername, sky)
	local player = minetest.get_player_by_name(playername)
	if player == nil or	not player.get_stars then return end
	player:set_sky(sky.sky_data)
	player:set_clouds(sky.cloud_data)
	player:set_moon(sky.moon_data)
	player:set_sun(sky.sun_data)
	player:set_stars(sky.star_data)
end

function skybox.update(playername)
	local p_layers = layers[playername]
	local sky = table.copy(default_sky)
	if p_layers == nil then p_layers = {} end
	local numbered_layers = {}
	for layer, values in pairs(p_layers) do
		table.insert(numbered_layers, values)
	end
	table.sort(numbered_layers, function(left, right)
		if left.priority == nil then left.priority = 1 end
		if right.priority == nil then right.priority = 1 end
		return left.priority < right.priority
	end)
	for i = 1, #numbered_layers do
		sky = merge_tables(sky, numbered_layers[i])
	end
	set_skybox(playername, sky)
end

function skybox.add(playername, name, sky)
	if layers[playername] == nil then layers[playername] = {} end
	layers[playername][name] = sky
end

function skybox.remove(playername, name)
	if layers[playername] == nil or layers[playername][name] == nil then return end
	layers[playername][name] = nil
end

minetest.register_on_leaveplayer(function(player)
	local playername = player:get_player_name()
	layers[playername] = nil
end)

return skybox