MeseCraft/mods/PLAYER/player_monoids/init.lua

-- Copyright (c) raymoo 2016
-- Licensed under Apache 2.0 license. See COPYING for details.

-- Any documentation here are internal details, please avoid using them in your
-- mod.

local modpath = minetest.get_modpath(minetest.get_current_modname()) .. "/"

player_monoids = {}

local mon_meta = {}

mon_meta.__index = mon_meta

local nop = function() end

-- A monoid object is a table with the following fields:
--   def: The monoid definition
--   player_map: A map from player names to their effect tables. Effect tables
--     are maps from effect IDs to values.
--   value_cache: A map from player names to the cached value for the monoid.
--   next_id: The next unique ID to assign an effect.

local function monoid(def)
	local mon = {}

	local actual_def = {}

	for k, v in pairs(def) do
		actual_def[k] = v
	end

	if not actual_def.apply then
		actual_def.apply = nop
	end

	if not actual_def.on_change then
		actual_def.on_change = nop
	end

	mon.def = actual_def

	local p_map = {}
        mon.player_map = p_map

	mon.next_id = 1

	local v_cache = {}
	mon.value_cache = v_cache

	setmetatable(mon, mon_meta)

	minetest.register_on_leaveplayer(function(player)
		local p_name = player:get_player_name()
		p_map[p_name] = nil
		v_cache[p_name] = nil
	end)

	return mon
end

player_monoids.make_monoid = monoid

function mon_meta:add_change(player, value, id)
	local p_name = player:get_player_name()

	local def = self.def

	local p_effects = self.player_map[p_name]
	if p_effects == nil then
		p_effects = {}
		self.player_map[p_name] = p_effects
	end

	local actual_id

	if id then
		actual_id = id
	else
		actual_id = self.next_id
		self.next_id = actual_id + 1
	end

	local old_total = self.value_cache[p_name]
	p_effects[actual_id] = value
	local new_total = def.fold(p_effects)
	self.value_cache[p_name] = new_total

	def.apply(new_total, player)
	def.on_change(old_total, new_total, player)

	return actual_id
end

function mon_meta:del_change(player, id)
	local p_name = player:get_player_name()

	local def = self.def

	local p_effects = self.player_map[p_name]
	if p_effects == nil then return end

	local old_total = self.value_cache[p_name]
	p_effects[id] = nil
	local new_total = def.fold(p_effects)
	self.value_cache[p_name] = new_total

	def.apply(new_total, player)
	def.on_change(old_total, new_total, player)
end

function mon_meta:value(player)
	local p_name = player:get_player_name()
	return self.value_cache[p_name] or self.def.identity
end

dofile(modpath .. "standard_monoids.lua")
dofile(modpath .. "test.lua")