"""SMTP delivery of the digest.

Works with Microsoft 365 and Google Workspace, both of which need an
app-specific password (or a mailbox with SMTP AUTH enabled) -- your normal
account password will be rejected if MFA is on. See README for the exact
settings for each.
"""

from __future__ import annotations

import logging
import smtplib
import ssl
from email.message import EmailMessage
from email.utils import formataddr, formatdate, make_msgid
from pathlib import Path

from ..config import EmailConfig

log = logging.getLogger(__name__)


class EmailError(RuntimeError):
    pass


def validate(cfg: EmailConfig, dry_run: bool = False) -> list[str]:
    """Return a list of configuration problems, empty if it looks sendable.

    ``dry_run`` relaxes the credential check: a dry run never opens a
    connection, so demanding a mail password before it will even build the
    report is pure obstruction -- and it hides the report the person was
    actually trying to look at.
    """
    problems: list[str] = []
    if not cfg.enabled:
        problems.append("email.enabled is false in config.toml")
    if not cfg.smtp_host:
        problems.append("email.smtp_host is not set")
    if not cfg.from_addr:
        problems.append("email.from_addr is not set")
    if not cfg.to:
        problems.append("email.to has no recipients")
    if cfg.username and not cfg.password and not dry_run:
        problems.append(
            "email.username is set but no password found -- set the "
            "AVWATCH_SMTP_PASSWORD environment variable"
        )
    if cfg.use_ssl and cfg.use_starttls:
        problems.append("use_ssl and use_starttls are mutually exclusive")
    return problems


def build_message(
    cfg: EmailConfig,
    subject: str,
    html_body: str,
    text_body: str,
    attachment: Path | None = None,
) -> EmailMessage:
    msg = EmailMessage()
    msg["Subject"] = f"{cfg.subject_prefix} {subject}".strip()
    msg["From"] = formataddr((cfg.from_name, cfg.from_addr))
    msg["To"] = ", ".join(cfg.to)
    if cfg.cc:
        msg["Cc"] = ", ".join(cfg.cc)
    msg["Date"] = formatdate(localtime=True)
    msg["Message-ID"] = make_msgid(domain=cfg.from_addr.split("@")[-1] or None)
    # Digests are informational; keep them out of vacation-responder loops.
    msg["Auto-Submitted"] = "auto-generated"

    msg.set_content(text_body)
    msg.add_alternative(html_body, subtype="html")

    if attachment and cfg.attach_html:
        path = Path(attachment)
        if path.exists():
            msg.add_attachment(
                path.read_bytes(),
                maintype="text",
                subtype="html",
                filename=path.name,
            )
        else:
            log.warning("attachment not found, sending without it: %s", path)

    return msg


def send(
    cfg: EmailConfig,
    subject: str,
    html_body: str,
    text_body: str,
    attachment: Path | None = None,
    dry_run: bool = False,
) -> str:
    """Send the digest. Returns a human-readable result line."""
    problems = validate(cfg, dry_run=dry_run)
    if problems:
        raise EmailError("email not configured: " + "; ".join(problems))

    msg = build_message(cfg, subject, html_body, text_body, attachment)
    recipients = list(cfg.to) + list(cfg.cc)

    if dry_run:
        return (
            f"[dry run] would send {msg['Subject']!r} to "
            f"{', '.join(recipients)} via {cfg.smtp_host}:{cfg.smtp_port}"
        )

    context = ssl.create_default_context()
    try:
        if cfg.use_ssl:
            with smtplib.SMTP_SSL(cfg.smtp_host, cfg.smtp_port,
                                  context=context, timeout=60) as smtp:
                if cfg.username:
                    smtp.login(cfg.username, cfg.password)
                smtp.send_message(msg, to_addrs=recipients)
        else:
            with smtplib.SMTP(cfg.smtp_host, cfg.smtp_port, timeout=60) as smtp:
                smtp.ehlo()
                if cfg.use_starttls:
                    smtp.starttls(context=context)
                    smtp.ehlo()
                if cfg.username:
                    smtp.login(cfg.username, cfg.password)
                smtp.send_message(msg, to_addrs=recipients)
    except smtplib.SMTPAuthenticationError as exc:
        raise EmailError(
            f"SMTP rejected the login ({exc.smtp_code}). With Microsoft 365 or "
            "Google Workspace you need an app password, not the account "
            "password, and SMTP AUTH must be enabled for the mailbox."
        ) from exc
    except smtplib.SMTPException as exc:
        raise EmailError(f"SMTP error: {exc}") from exc
    except OSError as exc:
        raise EmailError(
            f"could not reach {cfg.smtp_host}:{cfg.smtp_port}: {exc}"
        ) from exc

    return f"sent {msg['Subject']!r} to {', '.join(recipients)}"