from __future__ import annotations

import json
import os
from dataclasses import dataclass
from pathlib import Path
from typing import Any, Mapping, Optional, Union

from .exceptions import ClientConfigurationError

ConfigPath = Union[str, Path]

DEFAULT_BASE_URL_FALLBACK = "https://brecaldevel.bsmd-emswe.eu"
CONFIG_FILENAME = "client.json"


def _default_config_path() -> Path:
    xdg = Path(os.environ.get("XDG_CONFIG_HOME", Path.home() / ".config"))
    return (xdg / "brecal" / CONFIG_FILENAME).expanduser()


@dataclass(frozen=True)
class ClientConfig:
    base_url: str
    environment: Optional[str] = None

    @classmethod
    def from_mapping(cls, data: Mapping[str, Any]) -> "ClientConfig":
        environment = data.get("environment")
        base_url = data.get("base_url")
        endpoints = data.get("endpoints")

        if isinstance(endpoints, Mapping):
            if environment and environment in endpoints:
                base_url = endpoints[environment]
            elif not base_url and endpoints:
                # Pick the first entry as a last resort
                _, base_url = next(iter(endpoints.items()))

        if not base_url:
            raise ClientConfigurationError(
                "Client configuration requires either 'base_url' or an "
                "'endpoints' mapping."
            )

        return cls(
            base_url=str(base_url).rstrip("/"),
            environment=str(environment) if environment else None,
        )

    @classmethod
    def load(cls, path: Optional[ConfigPath] = None) -> "ClientConfig":
        file_path = Path(path) if path else _default_config_path()
        data = json.loads(file_path.read_text(encoding="utf-8"))
        return cls.from_mapping(data)


def get_default_base_url(path: Optional[ConfigPath] = None) -> str:
    """Resolve the default base URL using env vars or ~/.config/brecal/client.json."""
    env_override = os.getenv("BRECAL_BASE_URL")
    if env_override:
        return env_override.rstrip("/")

    try:
        config = ClientConfig.load(path=path)
        return config.base_url
    except FileNotFoundError:
        return DEFAULT_BASE_URL_FALLBACK
    except ClientConfigurationError:
        raise
    except Exception as exc:
        raise ClientConfigurationError(
            f"Failed to load BreCal client configuration: {exc}"
        ) from exc