from __future__ import annotations

import smtplib
from email.message import EmailMessage
from typing import TYPE_CHECKING

from app.core.config import settings

if TYPE_CHECKING:
    from collections.abc import Sequence


def send_email(
    *,
    subject: str,
    recipients: Sequence[str],
    text_body: str,
    html_body: str | None = None,
    reply_to: str | None = None,
) -> None:
    host = settings.SMTP_HOST
    from_email = settings.SMTP_FROM_EMAIL
    recipient_list = list(recipients)
    encryption = _get_smtp_encryption()

    if not host:
        raise ValueError("SMTP_HOST must be configured")

    if not from_email:
        raise ValueError("SMTP_FROM_EMAIL must be configured")

    if not recipient_list:
        raise ValueError("At least one recipient is required")

    message = EmailMessage()
    message["Subject"] = subject
    message["From"] = _format_sender(from_email=from_email, from_name=settings.SMTP_FROM_NAME)
    message["To"] = ", ".join(recipient_list)

    if reply_to:
        message["Reply-To"] = reply_to

    message.set_content(text_body)

    if html_body is not None:
        message.add_alternative(html_body, subtype="html")

    smtp_client = _create_smtp_client(
        host=host,
        port=settings.SMTP_PORT,
        encryption=encryption,
        timeout=settings.SMTP_TIMEOUT,
    )

    try:
        smtp_client.ehlo()

        if encryption == "starttls":
            smtp_client.starttls()
            smtp_client.ehlo()

        if settings.SMTP_USERNAME:
            if settings.SMTP_PASSWORD is None:
                raise ValueError("SMTP_PASSWORD must be configured when SMTP_USERNAME is set")

            smtp_client.login(settings.SMTP_USERNAME, settings.SMTP_PASSWORD)

        smtp_client.send_message(message)
    finally:
        smtp_client.quit()


def _format_sender(*, from_email: str, from_name: str | None) -> str:
    if not from_name:
        return from_email

    return f"{from_name} <{from_email}>"


def _get_smtp_encryption() -> str:
    encryption = settings.SMTP_ENCRYPTION.strip().lower()
    if encryption in {"ssl/tls", "ssl-tls", "tls"}:
        return "ssl_tls"

    if encryption not in {"starttls", "ssl_tls"}:
        raise ValueError("SMTP_ENCRYPTION must be 'starttls' or 'ssl_tls'")

    return encryption


def _create_smtp_client(*, host: str, port: int, encryption: str, timeout: float) -> smtplib.SMTP:
    client_class = smtplib.SMTP_SSL if encryption == "ssl_tls" else smtplib.SMTP
    return client_class(host, port, timeout=timeout)