"""结账页检测（feat-chv-muse-p10，叶子模块，纯标准库）。

对齐 Muse 官方安全文（security.muse.ai 2026-09-08，见
docs/chv-muse-p10-gap.md）：已保存支付凭证的网站，浏览器内置
结账页检测，每次都弹出人工审批并展示确切购买详情。

本模块是纯函数，不启动浏览器、不联网、不读原始 DOM：
- 输入只有 URL + 无障碍树节点（与 P4 的 ``detect_form_risk``
  同输入形状——P2 的浏览器子代理只返回无障碍树快照，节点
  只有 role/name/label/type 等描述字段）；
- 输出 ``CheckoutVerdict``：是否结账页、置信度、命中原因、
  表单风险、页面金额文本；
- 确定性规则，不冒充模型分类器（见 P6 口径）。

诚实边界：启发式检测，不是 100% 检出——商户自定义结账页、
单页应用内嵌结账可能漏检。漏检时的安全底线在调用方
（``PaymentGate`` 拒绝任何未经审批的扣款），不在本模块
宣称“所有结账页都会被拦下”。

页面金额文本（``amount_text``）只作展示信号：扣款金额永远
以 ``PurchaseDetails``（订单数据）为准，页面文本是不受信任
输入（P6 口径），不得直接拿去扣款。
"""

import re
from dataclasses import dataclass, field
from urllib.parse import urlparse

# URL 路径段信号：结账步骤（高）与购物车（中，结账前一步）。
_CHECKOUT_SEGMENTS = ("checkout", "check-out", "payment", "pay",
                      "billing", "order-review", "place-order",
                      "confirm-order")
_CART_SEGMENTS = ("cart", "basket", "bag")

# 无障碍树节点文本信号（小写子串匹配）。
_PAYMENT_HINTS = ("card number", "credit card", "debit card",
                  "cardholder", "expiry", "expiration", "exp date",
                  "cvc", "cvv", "security code", "卡号", "信用卡",
                  "有效期", "安全码")
_ORDER_HINTS = ("place order", "pay now", "confirm purchase",
                "complete purchase", "checkout", "下单", "立即支付",
                "确认购买", "去支付", "提交订单")
_PASSWORD_HINTS = ("password", "密码")

_AMOUNT_RE = re.compile(
    r"[$€£¥]\s?\d[\d,]*(?:\.\d{1,2})?"
    r"|\b\d[\d,]*(?:\.\d{1,2})?\s?(?:USD|EUR|GBP|JPY|CNY)\b")


@dataclass
class CheckoutVerdict:
    """一次结账检测的结果（只含描述，不含任何凭证值）。"""

    is_checkout: bool
    confidence: str  # high / medium / low
    reasons: list = field(default_factory=list)
    form_risk: str | None = None  # payment / password / None
    amount_text: str | None = None


def _node_text(node: dict) -> str:
    """一个无障碍树节点的描述文本（role/name/label/type
    拼起来，小写；原始 DOM 从不到这里）。"""
    parts = [str(node.get(k, "")) for k in
             ("role", "name", "label", "type")]
    return " ".join(parts).lower()


def _url_level(url: str) -> str:
    """URL 信号档位：high（结账路径）/ medium（购物车）/
    none。只看 path，不看 query（query 里可能有订单号等
    敏感值，不进原因）。"""
    try:
        path = urlparse(url).path.lower()
    except ValueError:
        return "none"
    segments = [s for s in path.split("/") if s]
    if any(s in _CHECKOUT_SEGMENTS for s in segments):
        return "high"
    if any(s in _CART_SEGMENTS for s in segments):
        return "medium"
    return "none"


def _node_signals(nodes: list) -> tuple:
    """无障碍树信号：(支付字段, 密码字段, 下单按钮, 金额文本)。
    节点文本只作特征匹配，不存原文。"""
    payment = False
    password = False
    order = False
    amount: str | None = None
    for node in nodes or []:
        text = _node_text(node)
        if not text.strip():
            continue
        if any(h in text for h in _PAYMENT_HINTS):
            payment = True
        if any(h in text for h in _PASSWORD_HINTS):
            password = True
        if any(h in text for h in _ORDER_HINTS):
            order = True
        if amount is None:
            hit = _AMOUNT_RE.search(text)
            if hit:
                amount = hit.group(0)
    return payment, password, order, amount


def detect_checkout(url: str, nodes: list | None = None
                    ) -> CheckoutVerdict:
    """检测一个页面是否为结账页。

    判定（确定性规则）：支付字段在页 → 结账页（高置信）；
    结账路径 URL → 结账页（有下单按钮/金额则高，否则中）；
    下单按钮 + 金额文本 → 结账页（中置信）；只命中购物车
    路径 → 不是结账页（购物车是结账前一步）；其余 → 不是。
    ``form_risk``：支付字段在页为 ``payment``，否则密码字
    段在页为 ``password``，与 P4 的 ``detect_form_risk``
    口径一致。"""
    level = _url_level(url)
    has_payment, has_password, has_order, amount = _node_signals(
        nodes or [])
    reasons: list = []
    if level == "high":
        reasons.append("checkout_url")
    elif level == "medium":
        reasons.append("cart_url")
    if has_payment:
        reasons.append("payment_fields")
    if has_order:
        reasons.append("order_button")
    if amount is not None:
        reasons.append("amount_text")
    risk = "payment" if has_payment else (
        "password" if has_password else None)
    if has_payment:
        return CheckoutVerdict(True, "high", reasons, risk, amount)
    if level == "high":
        conf = "high" if has_order or amount else "medium"
        return CheckoutVerdict(True, conf, reasons, risk, amount)
    if has_order and amount is not None:
        return CheckoutVerdict(True, "medium", reasons, risk, amount)
    return CheckoutVerdict(False, "low", reasons, risk, amount)