"""数学选择题验证码：题目生成、选项按钮组装与按钮数据编解码。

按钮 data 格式为 ``v|<token>|<选项值>``：token 标识"当前这道题"，
答错换题后旧消息上的按钮因 token 不匹配而失效，防止回放旧题。
"""

from __future__ import annotations

import random
from dataclasses import dataclass
from uuid import uuid4

from qqbotsdk.api import button, keyboard

_BUTTON_PREFIX = "v"


@dataclass(slots=True)
class Captcha:
    """一道验证码；a/op/b 保留运算数便于测试与排查。"""

    question: str
    answer: int
    options: list[int]
    token: str
    a: int
    op: str
    b: int

    def body(self) -> str:
        """题面正文（不含欢迎/提示头），换题重发时复用。"""
        return f"### {self.a} {self.op} {self.b} = ?"

    def keyboard(self) -> dict:
        """选项按钮键盘，每行 2 个。"""
        rows = [
            [button(str(v), encode_button_data(self.token, v)) for v in self.options[i : i + 2]]
            for i in range(0, len(self.options), 2)
        ]
        return keyboard(*rows)


def encode_button_data(token: str, value: int) -> str:
    return f"{_BUTTON_PREFIX}|{token}|{value}"


def parse_button_data(data: str) -> tuple[str, int] | None:
    """解析按钮 data 为 (token, 选项值)；非本机器人按钮返回 None。"""
    parts = data.split("|")
    if len(parts) != 3 or parts[0] != _BUTTON_PREFIX:
        return None
    try:
        return parts[1], int(parts[2])
    except ValueError:
        return None


def welcome_markdown(cap: Captcha, timeout_minutes: int, subject: str = "新同学") -> str:
    """进群首题/测试指令消息（markdown + 按钮一起发）；subject 为称呼前缀。"""
    return (
        "**入群验证**\n"
        f"{subject}请在 **{timeout_minutes} 分钟内** 点击下方正确答案完成验证，"
        "超时未通过将被移出本群。\n\n" + cap.body()
    )


def retry_markdown(cap: Captcha) -> str:
    """答错后换题重发的消息。"""
    return "答错了，换一题再试试：\n\n" + cap.body()


def generate(option_count: int = 4) -> Captcha:
    """随机生成一道加减/乘法选择题；干扰项取答案邻域且互不重复。"""
    op = random.choice(("+", "-", "×"))
    match op:
        case "+":
            a, b = random.randint(1, 20), random.randint(1, 20)
        case "-":
            a = random.randint(5, 30)
            b = random.randint(1, a)  # 保证差非负
        case _:
            a, b = random.randint(2, 9), random.randint(2, 9)
    answer = a + b if op == "+" else a - b if op == "-" else a * b

    lo = max(0, answer - 12)
    distractors: set[int] = set()
    while len(distractors) < option_count - 1:
        cand = random.randint(lo, answer + 12)
        if cand != answer:
            distractors.add(cand)
    options = [answer, *distractors]
    random.shuffle(options)

    return Captcha(
        question=f"{a} {op} {b}",
        answer=answer,
        options=options,
        token=uuid4().hex[:12],
        a=a,
        op=op,
        b=b,
    )