Save players’ data on discovered recipes

Specifically, data on items/groups they have held.

init.lua

@@ -1,5 +1,6 @@
 local S = minetest.get_translator("mtg_craftguide")
 local esc = minetest.formspec_escape
+local storage = minetest.get_mod_storage()
 
 local player_data = {}
 local init_items = {}
@@ -408,26 +409,6 @@ local function on_receive_fields(player, fields)
 	end
 end
 
-minetest.register_on_joinplayer(function(player)
-	local name = player:get_player_name()
-	local info = minetest.get_player_information(name)
-
-	player_data[name] = {
-		filter = "",
-		pagenum = 1,
-		items = {},
-		held_items = {},
-		held_groups = {},
-		known_items = {},
-		lang_code = info.lang_code
-	}
-end)
-
-minetest.register_on_leaveplayer(function(player)
-	local name = player:get_player_name()
-	player_data[name] = nil
-end)
-
 sfinv.register_page("mtg_craftguide:craftguide", {
 	title = esc(S("Recipes")),
 	get = function(self, player, context)
@@ -559,4 +540,77 @@ minetest.register_on_craft(function(itemstack, player)
 		update_known_items(player, itemstack:get_name())
 end)
 
+-- Initialize player-data.
+-- If saved data is found, load previous held-items and held-groups data.
+function load_player_data(player)
+	local name = player:get_player_name()
+	local info = minetest.get_player_information(name)
+
+	player_data[name] = {
+		filter = "",
+		pagenum = 1,
+		items = {},
+		held_items = {},
+		held_groups = {},
+		known_items = {},
+		lang_code = info.lang_code
+	}
+
+	local saved_data_str = storage:get_string("player_" .. name)
+	local saved_data = minetest.deserialize(saved_data_str or "")
+	if saved_data_str and saved_data then
+		player_data[name].held_items = saved_data.held_items
+		player_data[name].held_groups = saved_data.held_groups
+	end
+end
+
+-- Go over held items, and make sure any recipes that can be done with
+-- them is listed in visible items.
+function init_player_known_items(player)
+	local name = player:get_player_name()
+	local data = player_data[name]
+
+	for item,_ in pairs(data.held_items) do
+		local outputs = known_crafting_outputs(data, item)
+		if outputs then
+			for _,output in pairs(outputs) do
+				data.known_items[output] = true
+			end
+		end
+	end
+end
+
+-- Save a player’s held-item and held-group data.
+function save_player_data(player)
+	local name = player:get_player_name()
+	local data = player_data[name]
+	if data then
+		storage:set_string("player_" .. name, minetest.serialize(data))
+	end
+end
+
+-- Save all players’ held-item and held-group data.
+function save_all_player_data()
+	for name,data in pairs(player_data) do
+		if data then
+			storage:set_string("player_" .. name, minetest.serialize(data))
+		end
+	end
+end
+
+minetest.register_on_joinplayer(function(player)
+	load_player_data(player)
+	init_player_known_items(player)
+
+	-- Init displayed items.
+	local data = player_data[player:get_player_name()]
+	data.items = visible_items(data)
+end)
+
+minetest.register_on_leaveplayer(function(player)
+	save_player_data(player)
+	player_data[player:get_player_name()] = nil -- Save memory!
+end)
+
+minetest.register_on_shutdown(save_all_player_data)