app/models/base.py

from bson import ObjectId
from pydantic import BaseModel, Field, field_validator, model_serializer
from pydantic_core import core_schema
from typing import Any


class PyObjectId(str):
    """Custom type that validates and serialises MongoDB ObjectIds."""

    @classmethod
    def __get_validators__(cls):
        yield cls.validate

    @classmethod
    def validate(cls, v: Any) -> "PyObjectId":
        if isinstance(v, ObjectId):
            return cls(str(v))
        if isinstance(v, str):
            if not ObjectId.is_valid(v):
                raise ValueError(f"Invalid ObjectId: {v!r}")
            return cls(v)
        raise ValueError(f"Cannot convert {type(v)} to ObjectId")

    @classmethod
    def __get_pydantic_core_schema__(cls, source_type: Any, handler: Any) -> Any:
        return core_schema.no_info_plain_validator_function(
            cls.validate,
            serialization=core_schema.to_string_ser_schema(),
        )


def mongo_doc_to_dict(doc: dict) -> dict:
    """Convert MongoDB document: stringify _id and remove internal keys."""
    if doc is None:
        return {}
    result = {}
    for k, v in doc.items():
        if k == "_id":
            result["id"] = str(v)
        elif isinstance(v, ObjectId):
            result[k] = str(v)
        else:
            result[k] = v
    return result