import json
import os
from dataclasses import dataclass
from pathlib import Path


DEFAULT_TIMEZONE = "UTC"
DEFAULT_POLL_SECONDS = 60


class ConfigFileError(RuntimeError):
    def __init__(self, path: Path, message: str):
        super().__init__(f"{path}: {message}")
        self.path = path
        self.message = message


@dataclass(frozen=True)
class WebAppConfig:
    data_dir: Path
    posts_dir: Path
    config_dir: Path
    users_file: Path
    timezone: str
    session_secret: str
    scheduler_poll_seconds: int


def load_webapp_config() -> WebAppConfig:
    data_dir = Path(os.environ.get("LINKKI_DATA_DIR", "data")).resolve()
    config_dir = data_dir / "config"
    posts_dir = data_dir / "posts"
    config_dir.mkdir(parents=True, exist_ok=True)
    posts_dir.mkdir(parents=True, exist_ok=True)

    config_path = config_dir / "app_config.json"
    config_data: dict[str, object] = {}
    if config_path.exists():
        try:
            config_data = json.loads(config_path.read_text(encoding="utf-8"))
        except json.JSONDecodeError as error:
            raise ConfigFileError(config_path, f"Invalid JSON: {error.msg}") from error

    timezone = str(config_data.get("timezone", DEFAULT_TIMEZONE))
    session_secret = str(config_data.get("session_secret", "change-me"))
    poll_seconds = int(config_data.get("scheduler_poll_seconds", DEFAULT_POLL_SECONDS))
    users_filename = str(config_data.get("users_file", "users.json"))

    return WebAppConfig(
        data_dir=data_dir,
        posts_dir=posts_dir,
        config_dir=config_dir,
        users_file=config_dir / users_filename,
        timezone=timezone,
        session_secret=session_secret,
        scheduler_poll_seconds=poll_seconds,
    )