import os
from typing import Optional

import pyodbc
from dotenv import find_dotenv, load_dotenv

# Force reload environment variables from repo .env, ignoring system vars.
load_dotenv(find_dotenv(), override=True)


def _get_required_env(name: str) -> str:
    value = os.getenv(name, "").strip()
    if not value:
        raise RuntimeError(f"Missing {name} environment variable.")
    return value


def _build_conn_str() -> str:
    explicit = os.getenv("MSSQL_CONN_STR", "").strip()
    if explicit:
        return explicit

    driver = os.getenv("MSSQL_DRIVER", "ODBC Driver 18 for SQL Server").strip()
    server = _get_required_env("MSSQL_SERVER")
    database = _get_required_env("MSSQL_DATABASE")
    user = _get_required_env("MSSQL_USER")
    password = _get_required_env("MSSQL_PASSWORD")
    encrypt = os.getenv("MSSQL_ENCRYPT", "yes").strip() or "yes"
    trust_cert = os.getenv("MSSQL_TRUST_SERVER_CERT", "yes").strip() or "yes"

    return (
        f"DRIVER={{{driver}}};"
        f"SERVER={server};"
        f"DATABASE={database};"
        f"UID={user};"
        f"PWD={password};"
        f"Encrypt={encrypt};"
        f"TrustServerCertificate={trust_cert};"
    )


def connect_to_mssql() -> Optional[pyodbc.Connection]:
    """Establish a connection to the Microsoft SQL Server database."""
    try:
        return pyodbc.connect(_build_conn_str())
    except pyodbc.Error as exc:
        print(f"Error connecting to MSSQL database: {exc}")
        return None