extends Node
## D-085 (#258): Game session lifecycle manager.
## Creates per-game save directories on New Game, resumes existing sessions,
## and handles quit-to-menu flow with save confirmation.
##
## All save dirs live under user://saves/<game-id>/ where game-id is
## <YYYYMMDD>-<HHMMSS>-<hex6> (e.g. "20260225-143022-a7b3f1").

const SAVES_DIR := "user://saves/"
const GAME_SCENE := "res://scenes/main.tscn"
const MENU_SCENE := "res://scenes/main_menu.tscn"

var _quit_dialog: ConfirmationDialog = null


## Generate a new game-id, create its save directory, and activate the session.
## Returns the new game-id string.
func new_game() -> String:
	var now := Time.get_datetime_dict_from_system()
	var timestamp := "%04d%02d%02d-%02d%02d%02d" % [
		now.year, now.month, now.day,
		now.hour, now.minute, now.second,
	]
	var rng := RandomNumberGenerator.new()
	var hex_seed := "%06x" % (rng.randi() & 0xFFFFFF)
	var game_id := "%s-%s" % [timestamp, hex_seed]
	var save_path := SAVES_DIR + game_id + "/"
	var err := DirAccess.make_dir_recursive_absolute(save_path)
	if err != OK:
		push_error("SessionManager: failed to create save dir %s: %s" % [
			save_path, error_string(err)])
		return ""
	GameState.current_game_id = game_id

	# #175: Generate world_seed for deterministic simulation (D-010, D-029).
	# Combines two randi() calls (u32 each) into 63-bit entropy range.
	# Mask bit 31 of the upper word before shifting to prevent signed overflow:
	# GDScript int is i64 — if bit 63 is set, MessagePack encodes as negative,
	# and Rust rmp_serde rejects negative values when deserializing as u64.
	GameState.world_seed = ((rng.randi() & 0x7FFFFFFF) << 32) | rng.randi()

	# Persist world_seed to save directory so resume_game() can restore it.
	# Without this, loaded sessions would send seed=0, breaking D-010 determinism.
	_write_seed_file(save_path, GameState.world_seed)

	return game_id


## Resume an existing game session by setting the active game-id.
## Restores world_seed and character_archetype from the save directory.
func resume_game(game_id: String) -> void:
	GameState.current_game_id = game_id
	var save_path := SAVES_DIR + game_id + "/"
	GameState.world_seed = _read_seed_file(save_path)
	GameState.character_archetype = _read_archetype_file(save_path)


## List all game directories under user://saves/ sorted by last-modified (most recent first).
## Returns Array of {game_id: String, modified_time: int, newest_save: String}.
func list_game_dirs() -> Array:
	var dir := DirAccess.open(SAVES_DIR)
	if dir == null:
		return []
	var results: Array = []
	dir.list_dir_begin()
	var entry := dir.get_next()
	while entry != "":
		if dir.current_is_dir() and not entry.begins_with("."):
			var dir_path := SAVES_DIR + entry + "/"
			var newest_save := _find_newest_save(dir_path)
			var mtime: int = 0
			if newest_save != "":
				mtime = FileAccess.get_modified_time(dir_path + newest_save)
			results.append({
				"game_id": entry,
				"modified_time": mtime,
				"newest_save": newest_save,
			})
		entry = dir.get_next()
	dir.list_dir_end()
	results.sort_custom(func(a: Dictionary, b: Dictionary) -> bool:
		return a.modified_time > b.modified_time)
	return results


## Show "Save before quitting?" confirmation dialog, then return to main menu.
## #554: The actual F5 save will be wired here once server supports SaveCommand.
func quit_to_menu() -> void:
	if _quit_dialog != null and is_instance_valid(_quit_dialog):
		return  # Dialog already open
	_quit_dialog = ConfirmationDialog.new()
	_quit_dialog.dialog_text = UIStrings.get_text("menu.confirm_quit")
	_quit_dialog.ok_button_text = UIStrings.get_text("menu.confirm_yes")
	_quit_dialog.cancel_button_text = UIStrings.get_text("menu.confirm_no")
	get_tree().root.add_child(_quit_dialog)
	_quit_dialog.confirmed.connect(_do_quit_to_menu)
	_quit_dialog.canceled.connect(_cleanup_quit_dialog)
	_quit_dialog.popup_centered()


func _do_quit_to_menu() -> void:
	_cleanup_quit_dialog()
	# #554: Trigger quicksave before navigating to menu.
	# send_input() buffers the command — defer scene change by one frame so
	# SimBridge._process() flushes the outbound buffer before teardown.
	if not GameState.current_game_id.is_empty():
		var path := "user://saves/" + GameState.current_game_id + "/quicksave.sav"
		SimBridge.send_input({
			"action": InputMapper.Action.SAVE_GAME,
			"timestamp_msec": Time.get_ticks_msec(),
			"action_data": {"path": path},
		})
		GameState.current_game_id = ""
		_navigate_to_menu.call_deferred()
	else:
		GameState.current_game_id = ""
		get_tree().change_scene_to_file(MENU_SCENE)


func _navigate_to_menu() -> void:
	get_tree().change_scene_to_file(MENU_SCENE)


func _cleanup_quit_dialog() -> void:
	if _quit_dialog != null and is_instance_valid(_quit_dialog):
		_quit_dialog.queue_free()
	_quit_dialog = null


## Write world_seed to a file in the save directory for session persistence.
func _write_seed_file(save_path: String, seed: int) -> void:
	var file := FileAccess.open(save_path + "world_seed", FileAccess.WRITE)
	if file == null:
		push_error("SessionManager: failed to write seed file: %s" % error_string(FileAccess.get_open_error()))
		return
	file.store_64(seed)


## Read world_seed from save directory. Returns 0 if file missing (legacy saves).
## Masks the sign bit on read: save files written before the signed-overflow fix
## may contain negative i64 values that Rust rmp_serde rejects as u64.
func _read_seed_file(save_path: String) -> int:
	var file := FileAccess.open(save_path + "world_seed", FileAccess.READ)
	if file == null:
		push_warning("SessionManager: no seed file in %s — using seed=0 (legacy save)" % save_path)
		return 0
	return file.get_64() & 0x7FFFFFFFFFFFFFFF


## Write character_archetype to save directory. Called after new_game() creates the dir.
func save_character_archetype(game_id: String, archetype: String) -> void:
	var save_path := SAVES_DIR + game_id + "/"
	var file := FileAccess.open(save_path + "character.txt", FileAccess.WRITE)
	if file == null:
		push_error("SessionManager: failed to write character.txt: %s" % error_string(FileAccess.get_open_error()))
		return
	file.store_string(archetype)


## Read character_archetype from save directory. Returns "detective" if missing (legacy saves).
func _read_archetype_file(save_path: String) -> String:
	var file := FileAccess.open(save_path + "character.txt", FileAccess.READ)
	if file == null:
		return "detective"
	return file.get_as_text().strip_edges()


func _find_newest_save(dir_path: String) -> String:
	var dir := DirAccess.open(dir_path)
	if dir == null:
		return ""
	var best_name := ""
	var best_time: int = 0
	dir.list_dir_begin()
	var entry := dir.get_next()
	while entry != "":
		if not dir.current_is_dir() and entry.ends_with(".sav"):
			var mtime := FileAccess.get_modified_time(dir_path + entry)
			if mtime > best_time:
				best_time = mtime
				best_name = entry
		entry = dir.get_next()
	dir.list_dir_end()
	return best_name