import os
import smtplib
from email.message import EmailMessage


def _truthy(v: str | None) -> bool:
    if v is None:
        return False
    return v.strip().lower() in ("1", "true", "yes", "on")


def send_email(*, to_email: str, subject: str, body_text: str):
    """Send a plain-text email using SMTP settings from:

    1) Environment variables (highest priority)
    2) Admin-configured settings stored in the database (AppSettings)

    Required env vars:
      - SMTP_HOST
      - SMTP_PORT
      - SMTP_USERNAME
      - SMTP_PASSWORD
      - SMTP_FROM (defaults to SMTP_USERNAME)

    Optional:
      - SMTP_STARTTLS (default: "1")
      - SMTP_TIMEOUT_SECONDS (default: "10")
      - SMTP_DEBUG (default: "0") - set to 1 to print SMTP conversation to console
    """

    # Pull optional defaults from DB (if available). This keeps backwards compatibility:
    # existing deployments that only use env vars keep working unchanged.
    db_defaults = {}
    try:
        # Local import to avoid import cycles and to keep this module lightweight.
        from flask import current_app

        from .extensions import db
        from .models import AppSettings

        # Only try if app context exists (send_email is called inside requests/CLI normally).
        _ = current_app  # noqa: F841
        s = db.session.get(AppSettings, 1)
        if s:
            db_defaults = {
                "host": s.smtp_host,
                "port": s.smtp_port,
                "username": s.smtp_username,
                "password": s.smtp_password,
                "from_email": s.smtp_from,
                "starttls": s.smtp_starttls,
                "timeout": s.smtp_timeout_seconds,
                "debug": s.smtp_debug,
            }
    except Exception:
        # Best-effort; if DB isn't ready we fall back to env vars only.
        db_defaults = {}

    host = os.environ.get("SMTP_HOST") or db_defaults.get("host")
    port = int(os.environ.get("SMTP_PORT") or db_defaults.get("port") or 587)
    username = os.environ.get("SMTP_USERNAME") or db_defaults.get("username")
    password = os.environ.get("SMTP_PASSWORD") or db_defaults.get("password")
    from_email = os.environ.get("SMTP_FROM") or db_defaults.get("from_email") or username
    starttls = _truthy(os.environ.get("SMTP_STARTTLS")) if os.environ.get("SMTP_STARTTLS") is not None else bool(
        db_defaults.get("starttls") if db_defaults.get("starttls") is not None else True
    )
    timeout = float(os.environ.get("SMTP_TIMEOUT_SECONDS") or db_defaults.get("timeout") or 10)
    debug = _truthy(os.environ.get("SMTP_DEBUG")) if os.environ.get("SMTP_DEBUG") is not None else bool(
        db_defaults.get("debug") or False
    )

    missing = []
    if not host:
        missing.append("SMTP_HOST")
    if not username:
        missing.append("SMTP_USERNAME")
    if not password:
        missing.append("SMTP_PASSWORD")
    if not from_email:
        missing.append("SMTP_FROM")
    if missing:
        raise RuntimeError(
            "Missing SMTP configuration: "
            + ", ".join(missing)
            + ". Set them as environment variables (or configure them in Admin → Settings)."
        )

    msg = EmailMessage()
    msg["From"] = from_email
    msg["To"] = to_email
    msg["Subject"] = subject
    # Helps when SMTP providers force the authenticated mailbox as envelope sender,
    # but still allow replies to go to the desired address.
    if from_email and username and from_email != username:
        msg["Reply-To"] = from_email
    msg.set_content(body_text)

    with smtplib.SMTP(host, port, timeout=timeout) as smtp:
        if debug:
            smtp.set_debuglevel(1)
        smtp.ehlo()
        if starttls:
            smtp.starttls()
            smtp.ehlo()
        smtp.login(username, password)

        # Pass explicit envelope-from to avoid falling back to the authenticated user.
        # Note: some SMTP providers will still override this for anti-spoofing.
        smtp.send_message(msg, from_addr=from_email, to_addrs=[to_email])