"""ArangoDB client singleton."""
import logging
from arango import ArangoClient
from django.conf import settings

logger = logging.getLogger(__name__)

_db = None


def get_db():
    """Get ArangoDB database connection (singleton)."""
    global _db
    if _db is None:
        hosts = settings.ARANGODB_INTERNAL_URL
        if not hosts.startswith("http"):
            hosts = f"http://{hosts}"

        client = ArangoClient(hosts=hosts)
        _db = client.db(
            settings.ARANGODB_DATABASE,
            username='root',
            password=settings.ARANGODB_PASSWORD,
        )
        logger.info(
            "Connected to ArangoDB: %s/%s",
            hosts,
            settings.ARANGODB_DATABASE,
        )
    return _db


def ensure_graph():
    """Ensure named graph exists for K_SHORTEST_PATHS queries."""
    db = get_db()
    graph_name = 'optovia_graph'

    if db.has_graph(graph_name):
        return db.graph(graph_name)

    logger.info("Creating graph: %s", graph_name)
    return db.create_graph(
        graph_name,
        edge_definitions=[{
            'edge_collection': 'edges',
            'from_vertex_collections': ['nodes'],
            'to_vertex_collections': ['nodes'],
        }],
    )