import os
import smtplib
from email.message import EmailMessage


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

    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
    """

    host = os.environ.get("SMTP_HOST")
    port = int(os.environ.get("SMTP_PORT", "587"))
    username = os.environ.get("SMTP_USERNAME")
    password = os.environ.get("SMTP_PASSWORD")
    from_email = os.environ.get("SMTP_FROM") or username
    starttls = os.environ.get("SMTP_STARTTLS", "1").lower() in ("1", "true", "yes", "on")
    timeout = float(os.environ.get("SMTP_TIMEOUT_SECONDS", "10"))
    debug = os.environ.get("SMTP_DEBUG", "0").lower() in ("1", "true", "yes", "on")

    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 in a local .env file)."
        )

    msg = EmailMessage()
    msg["From"] = from_email
    msg["To"] = to_email
    msg["Subject"] = subject
    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)
        smtp.send_message(msg)