import email.policy
import email.utils
from email.message import EmailMessage

import aiosmtplib
import dkim

from app.config import get_settings
from app.models import MailDomain

SMTP_POLICY = email.policy.SMTP.clone(max_line_length=998)


def build_message(
    *,
    sender: str,
    recipients: list[str],
    cc: list[str],
    subject: str,
    body_text: str,
    body_html: str | None,
    reply_to: str | None = None,
) -> EmailMessage:
    message = EmailMessage(policy=SMTP_POLICY)
    message["From"] = sender
    message["To"] = ", ".join(recipients)
    if cc:
        message["Cc"] = ", ".join(cc)
    if reply_to:
        message["Reply-To"] = reply_to
    message["Subject"] = subject
    message["Date"] = email.utils.formatdate(localtime=True)
    message["Message-ID"] = email.utils.make_msgid(domain=sender.split("@")[-1])
    message.set_content(body_text)
    if body_html:
        message.add_alternative(body_html, subtype="html")
    return message


def sign_message(message: EmailMessage, domain: MailDomain) -> bytes:
    raw_message = message.as_bytes(policy=SMTP_POLICY)
    signed_headers = [
        b"from",
        b"to",
        b"subject",
        b"date",
        b"message-id",
        b"mime-version",
        b"content-type",
    ]
    if message.get("Cc"):
        signed_headers.insert(3, b"cc")
    signature = dkim.sign(
        raw_message,
        domain.dkim_selector.encode(),
        domain.domain_name.encode(),
        domain.dkim_private_key.encode(),
        include_headers=signed_headers,
        canonicalize=(b"relaxed", b"relaxed"),
    )
    if not signature.endswith(b"\r\n"):
        signature += b"\r\n"
    return signature + raw_message


async def send_via_smtp(
    message_bytes: bytes,
    *,
    sender: str,
    recipients: list[str],
) -> None:
    settings = get_settings()
    await aiosmtplib.send(
        message_bytes,
        sender=sender,
        recipients=recipients,
        hostname=settings.smtp_host,
        port=settings.smtp_port,
        local_hostname=settings.smtp_client_hostname,
        username=settings.smtp_username or None,
        password=settings.smtp_password or None,
        start_tls=settings.smtp_use_tls,
        timeout=settings.smtp_timeout,
    )


async def deliver_email(
    *,
    sender: str,
    recipients: list[str],
    cc: list[str],
    bcc: list[str],
    subject: str,
    body_text: str,
    body_html: str | None,
    domain: MailDomain,
    reply_to: str | None = None,
) -> None:
    message = build_message(
        sender=sender,
        recipients=recipients,
        cc=cc,
        subject=subject,
        body_text=body_text,
        body_html=body_html,
        reply_to=reply_to,
    )
    signed = sign_message(message, domain)
    await send_via_smtp(
        signed,
        sender=sender,
        recipients=[*recipients, *cc, *bcc],
    )