from __future__ import annotations

import os
from dataclasses import dataclass


@dataclass(frozen=True)
class ServiceSettings:
    db_dsn: str

    @staticmethod
    def from_env() -> "ServiceSettings":
        dsn = (
            os.getenv("CLUSTERING_DB_DSN")
            or os.getenv("DATABASE_URL")
            or _build_dsn_from_parts()
        )
        if not dsn:
            raise RuntimeError(
                "No database connection configured. Set CLUSTERING_DB_DSN or DATABASE_URL, "
                "or provide CLUSTERING_DB_HOST / CLUSTERING_DB_PORT / CLUSTERING_DB_NAME / "
                "CLUSTERING_DB_USER / CLUSTERING_DB_PASSWORD."
            )
        return ServiceSettings(db_dsn=dsn)


def _build_dsn_from_parts() -> str | None:
    host = os.getenv("CLUSTERING_DB_HOST")
    database = os.getenv("CLUSTERING_DB_NAME")
    user = os.getenv("CLUSTERING_DB_USER")
    password = os.getenv("CLUSTERING_DB_PASSWORD")
    port = os.getenv("CLUSTERING_DB_PORT", "5432")

    if not host or not database or not user:
        return None

    if password:
        return f"postgresql://{user}:{password}@{host}:{port}/{database}"
    return f"postgresql://{user}@{host}:{port}/{database}"