#!/usr/bin/env python3
"""课前零食：用 8 位显微镜观察 bitset 运算。"""

from __future__ import annotations


WIDTH = 8
MASK = (1 << WIDTH) - 1


def ask(prompt: str, default: str) -> str:
    try:
        return input(prompt).strip() or default
    except EOFError:
        return default


def read_bits(prompt: str, default: str) -> int:
    raw = ask(prompt, default)
    if len(raw) != WIDTH or any(ch not in "01" for ch in raw):
        print(f"{raw!r} 不是 {WIDTH} 位 01 串；本次使用 {default}。")
        raw = default
    return int(raw, 2)


def bits(value: int) -> str:
    return format(value & MASK, f"0{WIDTH}b")


def members(value: int) -> list[int]:
    return [index for index in range(WIDTH) if (value >> index) & 1]


def show(name: str, value: int) -> None:
    print(f"{name:>7} = {bits(value)}，集合成员（最低位编号 0）={members(value)}")


def main() -> None:
    print("Bitset 显微镜：左边是高位，最右边是编号 0。")
    a = read_bits("A（回车为 10110110）： ", "10110110")
    b = read_bits("B（回车为 01101100）： ", "01101100")
    show("A", a)
    show("B", b)
    operation = ask("操作：all / & / | / ^ / << / >>（回车为 all）： ", "all")

    if operation in ("all", "&"):
        show("A & B", a & b)
        print("  每一位都问一次：两盏灯是否同时亮？")
    if operation in ("all", "|"):
        show("A | B", a | b)
    if operation in ("all", "^"):
        show("A ^ B", a ^ b)
    if operation in ("all", "<<", ">>"):
        shift_text = ask("平移多少格（回车为 2）： ", "2")
        try:
            shift = max(0, int(shift_text))
        except ValueError:
            shift = 2
        if operation in ("all", "<<"):
            show(f"A << {shift}", (a << shift) & MASK)
            print("  左移出去的 1 不会搬家到另一端；它们离开了这个固定长度集合。")
        if operation in ("all", ">>"):
            show(f"A >> {shift}", a >> shift)
            print("  右移时低位掉出集合，高位补 0。")
    print(f"\n置位数 popcount(A)={a.bit_count()}。8 位是演示，真实一字通常有 64 位。")


if __name__ == "__main__":
    main()