"""
Category lookups for topic_metadata.json.

Used by the router to resolve "compare this with other X" style queries
that reference the previous topic implicitly, without naming a second
topic explicitly (e.g. "compare BFS with other graph algorithms").
"""

import json
import os

import config
from logs.logger import get_logger

logger = get_logger(__name__)

_metadata_cache = None


def _load_metadata() -> dict:
    global _metadata_cache
    if _metadata_cache is None:
        if not os.path.exists(config.TOPIC_METADATA_PATH):
            logger.warning("topic_metadata.json not found; category lookups disabled.")
            _metadata_cache = {}
        else:
            with open(config.TOPIC_METADATA_PATH, "r", encoding="utf-8") as f:
                _metadata_cache = json.load(f)
    return _metadata_cache


def get_category(topic_name: str) -> str | None:
    """Returns the category string for a canonical topic name, or None."""
    for entry in _load_metadata().values():
        if entry.get("topic") == topic_name:
            return entry.get("category")
    return None


def get_sibling_topics(topic_name: str, exclude: list = None, limit: int = 2) -> list:
    """
    Returns up to `limit` other topic names sharing the same category as
    `topic_name` (e.g. siblings of "Breadth-First Search" in category
    "Graph Traversal" -> ["Depth-First Search", "Dijkstra's Algorithm"]).
    """
    exclude = set(exclude or []) | {topic_name}
    category = get_category(topic_name)
    if not category:
        return []

    siblings = [
        entry["topic"]
        for entry in _load_metadata().values()
        if entry.get("category") == category and entry.get("topic") not in exclude
    ]
    return siblings[:limit]