class_name CharacterCache
extends RefCounted
## Character pictures kept on disk in the [code]characters[/code] folder next to the
## settings, so each one is downloaded only when it changed on the server.
##
## [code]index.json[/code] in the folder records, for each picture, when the server last
## changed it and when it was downloaded:
## [codeblock]
## {"Crono.png": {"modified": 1730000000, "downloaded": 1730100000}}
## [/codeblock]
## A cached picture is used while the server's change time matches the index. Servers that
## can't tell when pictures changed answer 404 for [code]/character/details[/code]; then a
## cached picture is used until it is [constant MAX_AGE_SECONDS] old.

const FOLDER_NAME: String = "characters"
const INDEX_FILE_NAME: String = "index.json"
## How long a picture is used before downloading it again, when the server can't tell
## whether it changed.
const MAX_AGE_SECONDS: int = 7 * 24 * 60 * 60
## The change time of a picture when the server can't tell it.
const UNKNOWN_TIME: int = -1

# What index.json holds: name -> {"modified": int, "downloaded": int}
var _index: Dictionary = {}
# When the server last changed each picture on the list, or UNKNOWN_TIME
var _modified: Dictionary[String, int] = {}


## The folder the pictures are kept in.
static func folder() -> String:
	return Settings.config_dir().path_join(FOLDER_NAME)


## Fetches the names of the characters and calls [param on_done] with them as an
## [code]Array[String][/code]. Cached pictures of characters no longer on the server are
## deleted.
func load_list(on_done: Callable) -> void:
	_load_index()
	var details_fetched: Callable = func details_fetched(details: Array) -> void:
		_modified.clear()
		for character: CharacterDetails in details:
			_modified[character.name] = character.modified
		_list_loaded(on_done)
	MusicServerClient.fetch_character_details(details_fetched, _load_names_only.bind(on_done))


## Calls [param on_done] with the picture of [param character_name] as an [Image], from
## disk when the cached one is still fresh, otherwise from the server.
func fetch_image(character_name: String, on_done: Callable) -> void:
	var path: String = _file_path(character_name)
	if _is_fresh(character_name) && FileAccess.file_exists(path):
		var cached: Image = CharacterCard.image_from_bytes(FileAccess.get_file_as_bytes(path))
		if cached != null:
			on_done.call(cached)
			return
		GameLog.warning("The cached picture of ", character_name, " is broken")
	var image_fetched: Callable = func image_fetched(bytes: PackedByteArray) -> void:
		var picture: Image = CharacterCard.image_from_bytes(bytes)
		if picture == null:
			GameLog.warning("Could not load the picture of ", character_name)
			return
		_store(character_name, bytes)
		on_done.call(picture)
	MusicServerClient.fetch_character_image(character_name, image_fetched)


# Servers older than /character/details only list the names
func _load_names_only(on_done: Callable) -> void:
	var list_fetched: Callable = func list_fetched(list: Variant) -> void:
		_modified.clear()
		if list is Array:
			for character_name: Variant in list:
				_modified[str(character_name)] = UNKNOWN_TIME
		_list_loaded(on_done)
	MusicServerClient.fetch_character_list(list_fetched)


func _list_loaded(on_done: Callable) -> void:
	var removed: bool = false
	for character_name: String in _index.keys():
		if !_modified.has(character_name):
			DirAccess.remove_absolute(_file_path(character_name))
			_index.erase(character_name)
			removed = true
	if removed:
		_save_index()
	var names: Array[String] = []
	names.assign(_modified.keys())
	on_done.call(names)


func _is_fresh(character_name: String) -> bool:
	if !_index.has(character_name):
		return false
	var entry: Dictionary = _index[character_name]
	var modified: int = _modified.get(character_name, UNKNOWN_TIME)
	if modified != UNKNOWN_TIME:
		return int(entry.get("modified", UNKNOWN_TIME)) == modified
	var age: float = Time.get_unix_time_from_system() - float(entry.get("downloaded", 0))
	return age < MAX_AGE_SECONDS


func _store(character_name: String, bytes: PackedByteArray) -> void:
	DirAccess.make_dir_recursive_absolute(folder())
	var file: FileAccess = FileAccess.open(_file_path(character_name), FileAccess.WRITE)
	if file == null:
		GameLog.warning("Could not cache the picture of ", character_name, ": ",
				error_string(FileAccess.get_open_error()))
		return
	file.store_buffer(bytes)
	file.close()
	_index[character_name] = {
		"modified": _modified.get(character_name, UNKNOWN_TIME),
		"downloaded": int(Time.get_unix_time_from_system()),
	}
	_save_index()


func _load_index() -> void:
	_index = {}
	var path: String = folder().path_join(INDEX_FILE_NAME)
	if FileAccess.file_exists(path):
		var parsed: Variant = JSON.parse_string(FileAccess.get_file_as_string(path))
		if parsed is Dictionary:
			_index = parsed


func _save_index() -> void:
	var file: FileAccess = FileAccess.open(folder().path_join(INDEX_FILE_NAME),
			FileAccess.WRITE)
	if file != null:
		file.store_string(JSON.stringify(_index, "\t", true))


# The server's names are plain file names, but they are made safe anyway since they
# become paths on this computer
func _file_path(character_name: String) -> String:
	return folder().path_join(character_name.validate_filename())