import os
from dataclasses import dataclass


class ConfigError(Exception):
    pass


@dataclass
class DatabaseSettings:
    host: str
    port: int
    username: str
    password: str
    dbname: str

    @staticmethod
    def from_env() -> "DatabaseSettings":
        host = os.environ.get("APP_DATABASE_HOST")
        port = os.environ.get("APP_DATABASE_PORT")
        username = os.environ.get("APP_DATABASE_USERNAME")
        password = os.environ.get("APP_DATABASE_PASSWORD")
        dbname = os.environ.get("APP_DATABASE_NAME")

        if not host:
            raise ConfigError("No `host` variable provided!")
        if not port:
            raise ConfigError("No `port` variable provided!")
        if not username:
            raise ConfigError("No `username` variable provided!")
        if not password:
            raise ConfigError("No `password` variable provided!")
        if not dbname:
            raise ConfigError("No `dbname` variable provided!")

        return DatabaseSettings(host, int(port), username, password, dbname)