#!/usr/bin/python3

import smtplib
import subprocess
import sys

SMTP_HOST = "127.0.0.1"
SMTP_PORT = 10028

DECISION_SCRIPT = "/usr/local/sbin/srs-alias-decision.py"
SRS_MAP = "socketmap:inet:127.0.0.1:10003:forward"

EX_TEMPFAIL = 75
EX_UNAVAILABLE = 69


def run_command(args):
    result = subprocess.run(
        args,
        capture_output=True,
        text=True,
        timeout=30
    )

    if result.returncode != 0:
        raise RuntimeError(
            result.stderr.strip()
            or result.stdout.strip()
            or f"Exit-Code {result.returncode}"
        )

    return result.stdout.strip()


def determine_sender(sender, recipient, original_recipient):
    decision = run_command([
        DECISION_SCRIPT,
        sender,
        recipient,
        original_recipient
    ])

    if decision.startswith("NO_SRS:"):
        return sender

    if not decision.startswith("SRS:"):
        raise RuntimeError(
            f"Keine eindeutige SRS-Entscheidung: {decision}"
        )

    rewritten_sender = run_command([
        "/usr/sbin/postmap",
        "-q",
        sender,
        SRS_MAP
    ])

    if not rewritten_sender:
        raise RuntimeError("PostSRSd lieferte keinen Absender")

    if not rewritten_sender.lower().endswith("@srs.warenform.de"):
        raise RuntimeError(
            f"Unerwartete SRS-Domain: {rewritten_sender}"
        )

    if not rewritten_sender.upper().startswith(("SRS0=", "SRS1=")):
        raise RuntimeError(
            f"Ungueltige SRS-Adresse: {rewritten_sender}"
        )

    return rewritten_sender


def main():
    if len(sys.argv) not in (5, 6):
        print(
            "Aufruf: srs-forward.py "
            "sender recipient original_recipient queue_id [envid]",
            file=sys.stderr
        )
        return EX_TEMPFAIL

    sender, recipient, original_recipient, queue_id = sys.argv[1:5]
    envid = sys.argv[5] if len(sys.argv) == 6 else ""

    if envid.startswith("envid="):
        envid = envid[len("envid="):]

    try:
        envelope_sender = determine_sender(
            sender,
            recipient,
            original_recipient
        )

        message = sys.stdin.buffer.read()

        with smtplib.SMTP(
            SMTP_HOST,
            SMTP_PORT,
            timeout=30
        ) as smtp:
            smtp.ehlo()

            mail_options = []
            rcpt_options = []

            if envid:
                if not smtp.has_extn("dsn"):
                    raise RuntimeError(
                        "SMTP-Ziel unterstuetzt kein DSN/ENVID"
                    )
                mail_options.append(f"ENVID={envid}")

            if original_recipient and smtp.has_extn("dsn"):
                rcpt_options.append(
                    f"ORCPT=rfc822;{original_recipient}"
                )

            smtp.sendmail(
                envelope_sender,
                [recipient],
                message,
                mail_options=mail_options,
                rcpt_options=rcpt_options
            )

    except smtplib.SMTPRecipientsRefused as exc:
        codes = [
            code
            for code, response in exc.recipients.values()
        ]

        permanent = bool(codes) and all(
            500 <= code < 600 for code in codes
        )

        result = EX_UNAVAILABLE if permanent else EX_TEMPFAIL
        enhanced_status = "5.0.0" if permanent else "4.0.0"

        print(
            f"{enhanced_status} SRS queue_id={queue_id}: "
            f"SMTP-Empfaengerablehnung: {exc.recipients!r}",
            file=sys.stderr
        )
        return result

    except smtplib.SMTPResponseException as exc:
        code = exc.smtp_code
        result = EX_UNAVAILABLE if 500 <= code < 600 else EX_TEMPFAIL

        enhanced_status = "5.0.0" if result == EX_UNAVAILABLE else "4.0.0"

        print(
            f"{enhanced_status} SRS queue_id={queue_id}: "
            f"SMTP {code}: {exc.smtp_error!r}",
            file=sys.stderr
        )
        return result

    except (
        subprocess.TimeoutExpired,
        RuntimeError,
        smtplib.SMTPException,
        OSError
    ) as exc:
        print(
            f"SRS queue_id={queue_id}: temporaerer Fehler: {exc}",
            file=sys.stderr
        )
        return EX_TEMPFAIL

    return 0


if __name__ == "__main__":
    sys.exit(main())