"""风控模块共用的 SMTP 邮件发送服务。"""

from __future__ import annotations

import asyncio
import os
import smtplib
from collections.abc import Mapping
from email.message import EmailMessage
from email.utils import formatdate, make_msgid, parseaddr


class RiskSmtpConfigurationError(ValueError):
    """SMTP 配置缺失或格式无效。"""


class RiskSmtpSendError(RuntimeError):
    """SMTP 邮件发送失败。"""


class RiskSmtpMailService:
    """使用 ``RISK_SMTP_*`` 配置发送风控邮件。"""

    def __init__(self, *, environment: Mapping[str, str] | None = None) -> None:
        self.environment = environment if environment is not None else os.environ

    async def send(
        self,
        recipients: list[str],
        subject: str,
        content: str,
    ) -> dict[str, object]:
        return await asyncio.to_thread(
            self._send_sync,
            recipients,
            subject,
            content,
        )

    def _send_sync(
        self,
        recipients: list[str],
        subject: str,
        content: str,
    ) -> dict[str, object]:
        normalized = self._validated_recipients(recipients)
        host = self.environment.get("RISK_SMTP_HOST", "").strip()
        sender = self.environment.get("RISK_SMTP_SENDER", "").strip()
        if not host or not sender:
            raise RiskSmtpConfigurationError("SMTP 发件配置缺失")
        if not _is_email(sender):
            raise RiskSmtpConfigurationError("SMTP 发件地址格式无效")
        if not subject.strip() or not content.strip():
            raise RiskSmtpConfigurationError("邮件主题和正文不能为空")
        if "\r" in subject or "\n" in subject:
            raise RiskSmtpConfigurationError("邮件主题包含非法换行")

        message = EmailMessage()
        message["From"] = sender
        message["To"] = ", ".join(normalized)
        message["Subject"] = subject
        message["Date"] = formatdate(localtime=True)
        message["Message-ID"] = make_msgid(domain="risk-alert.local")
        message.set_content(content)

        port = int(self.environment.get("RISK_SMTP_PORT", "465"))
        use_ssl = _enabled(self.environment, "RISK_SMTP_USE_SSL", default=True)
        timeout = float(self.environment.get("RISK_SMTP_TIMEOUT_SECONDS", "30"))
        smtp_class = smtplib.SMTP_SSL if use_ssl else smtplib.SMTP
        try:
            with smtp_class(host, port, timeout=timeout) as connection:
                username = self.environment.get("RISK_SMTP_USERNAME", "").strip()
                password = self.environment.get("RISK_SMTP_PASSWORD", "")
                if username:
                    connection.login(username, password)
                connection.send_message(message)
        except smtplib.SMTPAuthenticationError as error:
            raise RiskSmtpSendError("SMTP 身份验证失败") from error
        except smtplib.SMTPRecipientsRefused as error:
            raise RiskSmtpSendError("收件人被邮件服务器拒绝") from error
        except smtplib.SMTPSenderRefused as error:
            raise RiskSmtpSendError("发件人被邮件服务器拒绝") from error
        except TimeoutError as error:
            raise RiskSmtpSendError("SMTP 连接超时") from error
        except OSError as error:
            raise RiskSmtpSendError(f"SMTP 连接失败：{error}") from error
        except smtplib.SMTPException as error:
            raise RiskSmtpSendError("SMTP 邮件发送失败") from error
        return {"status": "sent", "recipient_count": len(normalized)}

    @staticmethod
    def _validated_recipients(recipients: list[str]) -> list[str]:
        normalized: list[str] = []
        seen: set[str] = set()
        for value in recipients:
            recipient = value.strip()
            if not _is_email(recipient):
                raise RiskSmtpConfigurationError("收件人地址格式无效")
            lowered = recipient.lower()
            if lowered not in seen:
                normalized.append(recipient)
                seen.add(lowered)
        if not normalized:
            raise RiskSmtpConfigurationError("收件人不能为空")
        return normalized


def _enabled(environment: Mapping[str, str], name: str, *, default: bool = False) -> bool:
    value = environment.get(name)
    if value is None:
        return default
    return value.strip().lower() in {"1", "true", "yes", "on"}


def _is_email(value: str) -> bool:
    _, parsed = parseaddr(value)
    return bool(value and parsed == value and "@" in value and len(value) <= 254)