class_name Updater
extends Node
## Updates the game in place to the newest release: downloads the new game next to the
## running one, checks it, swaps the files and starts the new version.
##
## The game is one file on Windows and Linux (the game data is embedded). A running .exe
## can't be overwritten on Windows, but it can be renamed, so it is moved aside to
## [code]<exe>.old[/code], which [method remove_old_files] deletes at the next start. On
## Linux the new file simply replaces the running one.
##
## [member executable_path], [member os_name], [member in_editor], [member start_process]
## and [member quit] can be replaced, so tests choose the platform and nothing restarts.

## Where the newest release can be downloaded by hand.
const RELEASES_PAGE: String = "https://gitea.sanplex.xyz/Sansan/MusicPlayer/releases/latest"
## Added to the game's path for the downloaded new version.
const UPDATE_SUFFIX: String = ".update"
## Added to the game's path for the old version, on Windows.
const OLD_SUFFIX: String = ".old"
## rwxr-xr-x, for the new game on Linux.
const EXECUTABLE_PERMISSIONS: int = 0b111_101_101
## Seconds the whole download may take.
const DOWNLOAD_TIMEOUT: float = 900.0

## The running game's file.
var executable_path: String = OS.get_executable_path()
## The platform, as [method OS.get_name] names it.
var os_name: String = OS.get_name()
## Whether the game runs from the Godot editor, where there is no game file to replace.
var in_editor: bool = OS.has_feature("editor")
## Starts a program: [code](path: String, arguments: PackedStringArray) -> int[/code].
var start_process: Callable = OS.create_process
## Quits the game.
var quit: Callable

var _request: HTTPRequest
var _on_progress: Callable


func _init() -> void:
	quit = func() -> void: get_tree().quit()


func _process(_delta: float) -> void:
	if _request != null && _on_progress.is_valid():
		_on_progress.call(_request.get_downloaded_bytes(), _request.get_body_size())


## The release file to download for [param os_name]: the game itself to update in place,
## or, when not [param in_place], what a person downloads, which on Linux is the package
## with an installer. Empty when there is no release for the platform.
static func asset_for(for_os: String, in_place: bool) -> String:
	match for_os:
		"Windows":
			return "windows"
		"Linux":
			return "linux" if in_place else "linux-package"
	return ""


## Why the game can't update itself here, or empty when it can.
func can_update_in_place() -> String:
	if in_editor:
		return "The game runs from the Godot editor."
	if asset_for(os_name, true).is_empty():
		return "The game updates itself on Windows and Linux."
	var probe: String = executable_path + ".write-test"
	var file: FileAccess = FileAccess.open(probe, FileAccess.WRITE)
	if file == null:
		return "The game's folder %s can't be written to." % executable_path.get_base_dir()
	file.close()
	DirAccess.remove_absolute(probe)
	return ""


## Where the new version is downloaded to, next to the game so it can be renamed into
## place.
func update_path() -> String:
	return executable_path + UPDATE_SUFFIX


## Downloads the new game from [param url]. Calls [param on_progress] with the bytes
## downloaded and the total (-1 while unknown) every frame, then [param on_done] with the
## file's path once it is checked, or [param on_failed] with the reason.
func download(url: String, on_progress: Callable, on_done: Callable,
		on_failed: Callable) -> void:
	cancel()
	_on_progress = on_progress
	_request = HTTPRequest.new()
	_request.download_file = update_path()
	_request.timeout = DOWNLOAD_TIMEOUT
	add_child(_request)
	_request.request_completed.connect(_on_downloaded.bind(on_done, on_failed))
	var error: Error = _request.request(url)
	if error != OK:
		cancel()
		on_failed.call("The download could not start: " + error_string(error))


## Stops a download and deletes what was downloaded.
func cancel() -> void:
	if _request != null:
		_request.cancel_request()
		_request.queue_free()
		_request = null
	DirAccess.remove_absolute(update_path())


## Whether [param path] looks like the game for [param for_os]: a Windows program starts
## with "MZ", a Linux one with the ELF header. An error page saved by mistake does not.
static func check_file(path: String, for_os: String) -> bool:
	var file: FileAccess = FileAccess.open(path, FileAccess.READ)
	if file == null || file.get_length() < 4:
		return false
	var start: PackedByteArray = file.get_buffer(4)
	match for_os:
		"Windows":
			return start.slice(0, 2) == "MZ".to_ascii_buffer()
		"Linux":
			return start == PackedByteArray([0x7F, 0x45, 0x4C, 0x46])
	return false


## Puts the new game at [param update] in place of the game at [param exe]. On Windows
## the running game is moved aside first, and put back if the new one can't be moved in.
static func install(update: String, exe: String, for_os: String) -> Error:
	if for_os == "Windows":
		var old: String = exe + OLD_SUFFIX
		if FileAccess.file_exists(old):
			DirAccess.remove_absolute(old)
		var error: Error = DirAccess.rename_absolute(exe, old)
		if error != OK:
			return error
		error = DirAccess.rename_absolute(update, exe)
		if error != OK:
			DirAccess.rename_absolute(old, exe)
		return error
	FileAccess.set_unix_permissions(update, EXECUTABLE_PERMISSIONS)
	return DirAccess.rename_absolute(update, exe)


## Deletes what an update left next to the game at [param exe]: the old version, and a
## download that was not finished.
static func remove_old_files(exe: String) -> void:
	for suffix: String in [OLD_SUFFIX, UPDATE_SUFFIX]:
		if FileAccess.file_exists(exe + suffix):
			DirAccess.remove_absolute(exe + suffix)


## Starts the game again, now the new version, and quits this one.
func restart() -> void:
	start_process.call(executable_path, OS.get_cmdline_args())
	quit.call()


func _on_downloaded(result: int, response_code: int, _headers: PackedStringArray,
		_body: PackedByteArray, on_done: Callable, on_failed: Callable) -> void:
	var expected: int = _request.get_body_size()
	_request.queue_free()
	_request = null
	var reason: String = ""
	if result != HTTPRequest.RESULT_SUCCESS:
		reason = "The download failed. Check the connection and try again."
	elif response_code != 200:
		reason = "The download failed: the server answered %d." % response_code
	elif expected >= 0 && FileAccess.get_size(update_path()) != expected:
		reason = "The download stopped before the end. Try again."
	elif !check_file(update_path(), os_name):
		reason = "The downloaded file is not the game for %s." % os_name
	if !reason.is_empty():
		DirAccess.remove_absolute(update_path())
		on_failed.call(reason)
		return
	on_done.call(update_path())