# MIT License
# 
# Copyright (c) 2026 Tidepost contributors
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# 
# Exception: assets/glyphs.json contains rasterized glyph data derived from
# Noto Sans CJK JP (SIL Open Font License 1.1). See assets/NOTO-LICENSE.txt.
# Pyxel is an external dependency under its own MIT license.

"""不変の値を作り直し、前の状態を残す。"""
from dataclasses import dataclass, replace


@dataclass(frozen=True)
class State:
    x: int = 20
    bag: tuple = ()


def collect(state):
    return replace(state, x=state.x + 4, bag=state.bag + ("sheet",))


def main():
    before = State()
    history = [before]
    current = collect(before)
    print("before:", before.x, before.bag)
    print("current:", current.x, current.bag)
    current = history.pop()
    print("undo:", current.x, current.bag)


if __name__ == "__main__":
    main()