NTOS Notepad update (#96892)

## About The Pull Request

You can edit and save text files on your modular console through notepad
app. The only thing that was useful in
https://github.com/tgstation/tgstation/pull/96793
## Why It's Good For The Game

I think these are the basic features of any text editor
## Changelog
🆑
qol: Notepad can edit and save text files
/🆑

code/modules/modular_computers/file_system/programs/notepad.dm

@@ -9,6 +9,10 @@
 	program_icon = "book"
 	can_run_on_flags = PROGRAM_ALL
 	circuit_comp_type = /obj/item/circuit_component/mod_program/notepad
+
+	var/opened_file_uid
+	var/opened_file_on_disk = FALSE
+	var/opened_file_name = "Untitled"
 	var/written_note = "Congratulations on your station upgrading to the new NtOS and Thinktronic based collaboration effort, \
 		bringing you the best in electronics and software since 2467!\n\
 		To help with navigation, we have provided the following definitions:\n\
@@ -19,17 +23,99 @@
 		Quarter - Either sides of Aft\n\
 		Bow - Either sides of Fore"
 
+/datum/computer_file/program/notepad/proc/get_target_disk(opened_on_disk)
+	if(opened_on_disk && computer?.inserted_disk)
+		return computer.inserted_disk
+	return null
+
+/datum/computer_file/program/notepad/proc/find_text_file(uid, opened_on_disk, name)
+	var/obj/item/disk/computer/target_disk = get_target_disk(opened_on_disk)
+	var/datum/computer_file/data/text/file
+	if(uid)
+		file = computer.find_file_by_uid(uid, target_disk)
+	if(!file && length(name))
+		file = computer.find_file_by_full_name("[name].TXT", target_disk)
+	return file
+
+/datum/computer_file/program/notepad/proc/load_text_file(datum/computer_file/data/text/file)
+	written_note = file.stored_text
+	opened_file_uid = file.uid
+	opened_file_on_disk = !!file.disk_host
+	opened_file_name = file.filename
+
+/datum/computer_file/program/notepad/proc/save_text_file(mob/user, name, extension, note, uid, opened_on_disk)
+	var/obj/item/disk/computer/target_disk = get_target_disk(opened_on_disk)
+	var/datum/computer_file/data/text/file = find_text_file(uid, opened_on_disk, name)
+	if(file)
+		file.stored_text = note
+		file.calculate_size()
+		load_text_file(file)
+		return
+
+	var/datum/computer_file/data/text/new_file = create_text_file(extension)
+	new_file.filename = name
+	new_file.stored_text = note
+	new_file.calculate_size()
+	var/file_stored = target_disk ? target_disk.add_file(new_file) : computer.store_file(new_file, user)
+	if(!file_stored)
+		to_chat(user, span_warning("Error occured while saving the file!"))
+		qdel(new_file)
+		return
+
+	load_text_file(new_file)
+
+/datum/computer_file/program/notepad/proc/create_text_file(extension)
+	if(extension == "LOG")
+		return new /datum/computer_file/data/text/logfile()
+	return new /datum/computer_file/data/text()
+
 /datum/computer_file/program/notepad/ui_act(action, list/params, datum/tgui/ui, datum/ui_state/state)
 	. = ..()
+	var/mob/user = ui.user
 	switch(action)
 		if("UpdateNote")
 			written_note = params["newnote"]
 			return TRUE
+		if("SaveNote")
+			written_note = params["newnote"] || written_note
+			save_text_file(user, opened_file_name, null, written_note, opened_file_uid, opened_file_on_disk)
+			return TRUE
+		if("Save")
+			written_note = params["note"] || written_note
+			save_text_file(user, opened_file_name, null, written_note, opened_file_uid, opened_file_on_disk)
+			return TRUE
+		if("SaveAs")
+			var/new_name = trim(params["name"], MAX_MESSAGE_LEN)
+			var/extension = params["extension"]
+			if(!length(new_name) || !filter_filename_pda(new_name))
+				return
+			written_note = params["note"] || written_note
+			save_text_file(user, new_name, extension, written_note, params["uid"], opened_file_on_disk)
+			return TRUE
+		if("Open")
+			var/datum/computer_file/data/text/file = find_text_file(params["uid"], params["onDisk"], params["name"])
+			if(!file)
+				return
+			load_text_file(file)
+			return TRUE
 
 /datum/computer_file/program/notepad/ui_data(mob/user)
 	var/list/data = list()
 
 	data["note"] = written_note
+	data["documentName"] = opened_file_name
+	data["files"] = list()
+	if(computer)
+		for(var/datum/computer_file/file in computer.get_files(TRUE))
+			if(!istype(file, /datum/computer_file/data/text))
+				continue
+			data["files"] += list(list(
+				"uid" = file.uid,
+				"name" = file.filename,
+				"filetype" = file.filetype,
+				"onDisk" = !!file.disk_host,
+				"displayName" = "[file.filename].[file.filetype]",
+			))
 
 	return data