"""
dmsync - MongoDB Change Streams sync daemon
Watches local deskmeter database and pushes changes to remote MongoDB

Requires local MongoDB to be configured as a replica set.
Uses resume tokens to continue from last position after restart.
"""

import json
import logging
import os
from pathlib import Path

from pymongo import MongoClient
from pymongo.errors import PyMongoError

logging.basicConfig(
    level=logging.INFO, format="%(asctime)s [%(levelname)s] %(message)s"
)
log = logging.getLogger("dmsync")

RESUME_TOKEN_FILE = Path.home() / ".dmsync-resume-token"
REMOTE_HOST = os.environ.get("DMSYNC_REMOTE_HOST", "mcrn.ar")
REMOTE_PORT = int(os.environ.get("DMSYNC_REMOTE_PORT", 27017))
COLLECTIONS = ("switch", "task", "task_history", "state")


def load_resume_token():
    """Load resume token from file if exists."""
    if RESUME_TOKEN_FILE.exists():
        try:
            return json.loads(RESUME_TOKEN_FILE.read_text())
        except (json.JSONDecodeError, IOError) as e:
            log.warning(f"Failed to load resume token: {e}")
    return None


def save_resume_token(token):
    """Persist resume token to file."""
    try:
        RESUME_TOKEN_FILE.write_text(json.dumps(token))
    except IOError as e:
        log.error(f"Failed to save resume token: {e}")


def sync():
    """Main sync loop using Change Streams."""
    log.info(f"Connecting to local MongoDB...")
    local = MongoClient()

    log.info(f"Connecting to remote MongoDB at {REMOTE_HOST}:{REMOTE_PORT}...")
    remote = MongoClient(REMOTE_HOST, REMOTE_PORT)

    local_db = local.deskmeter
    remote_db = remote.deskmeter

    resume_token = load_resume_token()
    if resume_token:
        log.info("Resuming from saved token")

    watch_kwargs = {"resume_after": resume_token} if resume_token else {}
    watch_kwargs["full_document"] = "updateLookup"  # Get full doc on updates

    # Watch for inserts, updates, and replaces on the database
    pipeline = [{"$match": {"operationType": {"$in": ["insert", "update", "replace"]}}}]

    log.info(f"Watching collections: {', '.join(COLLECTIONS)}")

    try:
        with local_db.watch(pipeline, **watch_kwargs) as stream:
            for change in stream:
                collection = change["ns"]["coll"]

                if collection not in COLLECTIONS:
                    continue

                doc = change.get("fullDocument")
                if not doc:
                    continue

                # Upsert to remote
                result = remote_db[collection].replace_one(
                    {"_id": doc["_id"]}, doc, upsert=True
                )

                action = "inserted" if result.upserted_id else "updated"
                log.info(f"{collection}: {action} {doc['_id']}")

                save_resume_token(stream.resume_token)

    except PyMongoError as e:
        log.error(f"MongoDB error: {e}")
        raise


if __name__ == "__main__":
    log.info("Starting dmsync daemon")
    sync()