"""
Core utility functions shared across modules.
"""
from datetime import datetime
from typing import Dict, Any, Optional, List


def format_meta_field(document: Dict[str, Any]) -> Dict[str, Any]:
    """Group audit fields under 'meta' for API responses."""
    meta = {
        "created_by": document.get("created_by_username") or "Unknown",
        "created_by_id": str(document.get("created_by", "")),
        "created_at": document.get("created_at"),
    }
    if document.get("updated_by"):
        meta["updated_by_id"] = str(document["updated_by"])
        meta["updated_by"] = document.get("updated_by_username") or "Unknown"
    if document.get("updated_at"):
        meta["updated_at"] = document["updated_at"]

    audit_fields = ["created_by", "created_at", "created_by_username",
                    "updated_by", "updated_by_username", "updated_at"]
    formatted = {k: v for k, v in document.items() if k not in audit_fields}
    formatted["meta"] = meta
    formatted["created_by"] = document.get("created_by_username") or str(document.get("created_by", ""))
    formatted["created_at"] = document.get("created_at")
    if "updated_at" in document:
        formatted["updated_at"] = document.get("updated_at")
    return formatted


def extract_audit_fields(
    user_id: str,
    username: Optional[str] = None,
    is_update: bool = False
) -> Dict[str, Any]:
    """Return audit fields dict for DB insert/update."""
    if is_update:
        return {
            "updated_by": user_id,
            "updated_by_username": username or "Unknown",
            "updated_at": datetime.utcnow(),
        }
    return {
        "created_by": user_id,
        "created_by_username": username or "Unknown",
        "created_at": datetime.utcnow(),
    }


def build_projection(projection_list: Optional[List[str]]) -> Optional[Dict[str, int]]:
    """Build a MongoDB projection dict from a list of field names."""
    if not projection_list:
        return None
    proj = {field: 1 for field in projection_list}
    proj["_id"] = 0
    return proj