#!/usr/bin/env python3
"""
ics_mail_importer_env_v6.py
---------------------------
ICS-Importer für mailbox.org / CalDAV.

Verbesserungen in v6:
- CAL-4121-Konflikte werden als "bereits aktueller Serverstand" behandelt
- Timeout-Fehler beim CalDAV-Upload werden mit Retries und Backoff erneut versucht
- Netzwerk-/Timeout-Probleme werden getrennt von fachlichen Importfehlern protokolliert
- Mails werden nur bei erfolgreicher Verarbeitung oder erkanntem Konflikt als verarbeitet markiert

Optionale .env-Werte:
- CALDAV_TIMEOUT=90
- CALDAV_RETRIES=3
- CALDAV_RETRY_BACKOFF=5
"""

import imaplib
import email
import logging
import hashlib
import os
import time
from pathlib import Path
from datetime import datetime, timezone

from dotenv import load_dotenv
import caldav
from icalendar import Calendar

BASE_DIR = Path(__file__).resolve().parent
load_dotenv(BASE_DIR / ".env")

LOG_FILE = BASE_DIR / "ics_importer.log"
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] %(message)s",
    handlers=[logging.FileHandler(LOG_FILE), logging.StreamHandler()],
)
log = logging.getLogger(__name__)

SEEN_FILE = BASE_DIR / "imported_uids.txt"


def load_seen_uids():
    if not SEEN_FILE.exists():
        return set()
    return set(SEEN_FILE.read_text().splitlines())


def save_uid(uid: str):
    with SEEN_FILE.open("a") as f:
        f.write(uid + "\n")


def env_bool(name: str, default: str = "false") -> bool:
    return os.getenv(name, default).strip().lower() in {"1", "true", "yes", "on"}


def env_int(name: str, default: int) -> int:
    value = os.getenv(name)
    if value is None or not value.strip():
        return default
    return int(value.strip())


def exception_text(exc: Exception) -> str:
    return str(exc or "")


def is_newer_version_conflict(exc: Exception) -> bool:
    message = exception_text(exc).lower()
    patterns = [
        "412 precondition failed",
        "cal-4121",
        "newer version of the appointment already exists",
        "concurrent modification",
        "actual sequence",
        "client sequence",
    ]
    return sum(1 for pattern in patterns if pattern in message) >= 2


def is_timeout_error(exc: Exception) -> bool:
    message = exception_text(exc).lower()
    timeout_patterns = [
        "read timed out",
        "timeout",
        "timed out",
        "read timeout",
    ]
    return any(pattern in message for pattern in timeout_patterns)


def add_event_with_retries(calendar, ical_text: str, summary: str, uid: str, sequence, timeout: int, retries: int, backoff: int):
    last_exception = None

    for attempt in range(1, retries + 1):
        try:
            calendar.add_event(ical_text)
            log.info(f"    ✓ Termin importiert: {summary} [{uid[:20]}]")
            return "imported"
        except Exception as e:
            last_exception = e
            exc_name = type(e).__name__
            exc_message = exception_text(e)
            log.info(f"    Exception-Typ beim Import: {exc_name}")

            if is_newer_version_conflict(e):
                log.info(
                    f"    ↷ Konflikt ignoriert: Neuere Version existiert bereits: {summary} "
                    f"[{uid[:20]}], SEQUENCE={sequence}"
                )
                return "conflict"

            if is_timeout_error(e):
                if attempt < retries:
                    wait_seconds = backoff * attempt
                    log.warning(
                        f"    ⏳ Timeout beim Import von {uid[:20]} (Versuch {attempt}/{retries}, Timeout={timeout}s). "
                        f"Neuer Versuch in {wait_seconds}s ..."
                    )
                    time.sleep(wait_seconds)
                    continue
                log.warning(
                    f"    ✗ Timeout beim Import von {uid[:20]} nach {retries} Versuchen: {exc_message}"
                )
                return "timeout"

            log.warning(f"    ✗ Fehler beim Import von {uid[:20]}: {exc_message}")
            return "error"

    if last_exception is not None:
        raise last_exception
    return "error"


def import_ics_to_caldav(ics_bytes: bytes, uid_hash: str):
    caldav_url = os.getenv("CALDAV_URL")
    username = os.getenv("CALDAV_USERNAME")
    password = os.getenv("CALDAV_PASSWORD")
    timeout = env_int("CALDAV_TIMEOUT", 90)
    retries = env_int("CALDAV_RETRIES", 3)
    backoff = env_int("CALDAV_RETRY_BACKOFF", 5)

    if not caldav_url or not username or not password:
        raise RuntimeError(
            "CALDAV_URL, CALDAV_USERNAME oder CALDAV_PASSWORD fehlt in .env"
        )

    client = caldav.DAVClient(url=caldav_url, username=username, password=password, timeout=timeout)
    calendar = client.calendar(url=caldav_url)
    cal = Calendar.from_ical(ics_bytes)

    imported = 0
    conflicts = 0
    timeouts = 0
    errors = 0

    for component in cal.walk():
        if component.name != "VEVENT":
            continue

        single_cal = Calendar()
        single_cal.add("prodid", "-//ics_mail_importer//DE")
        single_cal.add("version", "2.0")
        single_cal.add_component(component)

        uid = str(component.get("uid", uid_hash + f"-{imported + conflicts + timeouts + errors}"))
        summary = str(component.get("summary", "(kein Titel)"))
        sequence = component.get("sequence", "(keine sequence)")
        result = add_event_with_retries(
            calendar,
            single_cal.to_ical().decode("utf-8"),
            summary,
            uid,
            sequence,
            timeout,
            retries,
            backoff,
        )

        if result == "imported":
            imported += 1
        elif result == "conflict":
            conflicts += 1
        elif result == "timeout":
            timeouts += 1
        else:
            errors += 1

    return imported, conflicts, timeouts, errors


def process_mailbox():
    host = os.getenv("IMAP_HOST", "imap.mailbox.org")
    port = int(os.getenv("IMAP_PORT", "993"))
    username = os.getenv("IMAP_USERNAME")
    password = os.getenv("IMAP_PASSWORD")
    folder = os.getenv("IMAP_FOLDER", "INBOX")

    if not username or not password:
        raise RuntimeError("IMAP_USERNAME oder IMAP_PASSWORD fehlt in .env")

    unseen_only = env_bool("IMAP_UNSEEN_ONLY", "true")
    mark_as_read = env_bool("IMAP_MARK_AS_READ", "false")

    log.info(f"Verbinde mit IMAP {host}:{port} als {username} ...")
    conn = imaplib.IMAP4_SSL(host, port)
    conn.login(username, password)

    conn.select(folder)
    criteria = "UNSEEN" if unseen_only else "ALL"
    typ, data = conn.uid("search", None, criteria)
    if typ != "OK":
        raise RuntimeError("IMAP-Suche fehlgeschlagen")

    message_uids = data[0].split()
    log.info(f"{len(message_uids)} Nachricht(en) zur Prüfung gefunden.")

    imported_hashes = load_seen_uids()
    total_imported = 0
    total_conflicts = 0
    total_timeouts = 0
    total_errors = 0
    processed_mail_count = 0

    for msg_uid in message_uids:
        typ, fetched = conn.uid("fetch", msg_uid, "(BODY.PEEK[])")
        if typ != "OK" or not fetched or not fetched[0]:
            log.warning(f"Konnte Nachricht UID {msg_uid.decode()} nicht abrufen.")
            continue

        raw = fetched[0][1]
        msg = email.message_from_bytes(raw)

        mail_had_ics = False
        mail_processed = False
        subject = msg.get("Subject", "(ohne Betreff)")
        log.info(f"Prüfe Mail UID {msg_uid.decode()} – Betreff: {subject}")

        for part in msg.walk():
            content_type = part.get_content_type()
            filename = part.get_filename() or ""
            is_ics = content_type in ("text/calendar", "application/ics") or filename.lower().endswith(".ics")
            if not is_ics:
                continue

            ics_bytes = part.get_payload(decode=True)
            if not ics_bytes:
                continue

            mail_had_ics = True
            uid_hash = hashlib.sha256(ics_bytes).hexdigest()

            if uid_hash in imported_hashes:
                log.info(f"  Überspringe bereits verarbeiteten ICS-Anhang {filename!r} ({uid_hash[:12]}…)")
                mail_processed = True
                continue

            log.info(f"  ICS-Anhang gefunden: {filename!r} ({uid_hash[:12]}…)")

            try:
                imported_count, conflict_count, timeout_count, error_count = import_ics_to_caldav(ics_bytes, uid_hash)
                total_imported += imported_count
                total_conflicts += conflict_count
                total_timeouts += timeout_count
                total_errors += error_count

                if imported_count > 0 or conflict_count > 0:
                    save_uid(uid_hash)
                    imported_hashes.add(uid_hash)
                    mail_processed = True
                else:
                    log.warning(
                        f"  Kein VEVENT erfolgreich verarbeitet für Anhang {filename!r}; Mail bleibt ungelesen."
                    )
            except Exception as e:
                log.warning(
                    f"  Fehler beim Verarbeiten von {filename!r}: {e}; Mail bleibt ungelesen."
                )

        if mark_as_read and mail_processed:
            store_typ, _ = conn.uid("store", msg_uid, "+FLAGS", "(\\Seen)")
            if store_typ == "OK":
                processed_mail_count += 1
                log.info(f"Mail UID {msg_uid.decode()} erfolgreich verarbeitet und als gelesen markiert.")
            else:
                log.warning(
                    f"Mail UID {msg_uid.decode()} wurde verarbeitet, konnte aber nicht als gelesen markiert werden."
                )
        elif mark_as_read and mail_had_ics and not mail_processed:
            log.info(f"Mail UID {msg_uid.decode()} hatte ICS-Anhang, aber keine erfolgreiche Verarbeitung; bleibt ungelesen.")

    conn.close()
    conn.logout()

    log.info(f"Fertig. {total_imported} Termin(e) importiert.")
    log.info(f"{total_conflicts} Konflikt(e) als bereits aktueller Serverstand erkannt.")
    log.info(f"{total_timeouts} Timeout-Fall/Fälle beim CalDAV-Upload.")
    log.info(f"{total_errors} sonstige Fehler beim CalDAV-Upload.")
    log.info(f"{processed_mail_count} Mail(s) als gelesen markiert.")


def main():
    log.info("=" * 60)
    log.info(f"ICS-Importer gestartet ({datetime.now(timezone.utc).isoformat()})")
    process_mailbox()
    log.info("=" * 60)


if __name__ == "__main__":
    main()