import os
import json
from dataclasses import dataclass, fields
from typing import Any

class ConfigException (Exception): pass

def default_env_loader(var_name, default_value=None):
    v = os.getenv(var_name, default_value)
    if not v:
        raise ConfigException(var_name)
    return v

def json_env_loader(var_name):
    v = default_env_loader(var_name)
    vv = json.loads(v)
    return vv

@dataclass(init=False, frozen=False)
class Config:
    MQTT_BROKER : str
    MQTT_PORT : int
    MQTT_CLIENT_PREFIX : str
    BOXES : dict
    BOX_TOPIC_PREFIXES : dict
    CENTRAL_TOPICS : dict
    OFF_TEMPERATURE : str
    LOW_TEMPERATURE : str
    MAINTENANCE_TEMPERATURE : str
    DEFAULT_HIGH_TEMPERATURE : str
    STATUS_TOPIC : str
    CONTEXT_TOPIC_PREFIX : str

    def __init__(self):
        for f in fields(self):
            v = os.getenv(f.name)
            if not v:
                raise ConfigException(f.name)
            if f.type == int:
                v = int(v)
            elif f.type == dict:
                v = json.loads(v)
            setattr(self, f.name, v)