存档基础：先把一个事实安全地读回来

extends Node
const PATH: String = "user://learning_flag.json"
var has_examined: bool = false

func save_practice() -> Error:
    var file: FileAccess = FileAccess.open(PATH, FileAccess.WRITE)
    if file == null:
        return FileAccess.get_open_error()
    var payload: Dictionary[String, Variant] = {
        "schema_version": 1,
        "has_examined": has_examined
    }
    file.store_string(JSON.stringify(payload))
    file.flush()
    var error: Error = file.get_error()
    file.close()
    return error

func load_practice() -> Error:
    if not FileAccess.file_exists(PATH):
        return ERR_FILE_NOT_FOUND
    var file: FileAccess = FileAccess.open(PATH, FileAccess.READ)
    if file == null:
        return FileAccess.get_open_error()
    if file.get_length() > 65536:
        file.close()
        return ERR_INVALID_DATA
    var text: String = file.get_as_text()
    file.close()
    var parser: JSON = JSON.new()
    var error: Error = parser.parse(text)
    if error != OK:
        return error
    var value: Variant = parser.data
    if not value is Dictionary:
        return ERR_INVALID_DATA
    var data: Dictionary = value
    var version: Variant = data.get("schema_version")
    if not (version is int or version is float):
        return ERR_INVALID_DATA
    if float(version) != 1.0:
        return ERR_INVALID_DATA
    var flag: Variant = data.get("has_examined")
    if not flag is bool:
        return ERR_INVALID_DATA
    has_examined = bool(flag)
    return OK