import os
from dataclasses import dataclass
from pathlib import Path

from dotenv import load_dotenv

ROOT_DIR = Path(__file__).resolve().parent.parent
DEFAULT_COMMENT_FILE = ROOT_DIR / "comment.txt"


@dataclass(frozen=True)
class Config:
    bot_token: str
    discussion_chat_id: int
    comment_text: str


def _load_comment_text() -> str:
    path_raw = os.getenv("COMMENT_FILE", "").strip()
    path = Path(path_raw) if path_raw else DEFAULT_COMMENT_FILE
    if not path.is_absolute():
        path = ROOT_DIR / path

    if not path.is_file():
        raise SystemExit(
            f"Comment file not found: {path}. "
            "Create comment.txt in the project root or set COMMENT_FILE."
        )

    text = path.read_text(encoding="utf-8").strip()
    if not text:
        raise SystemExit(f"Comment file is empty: {path}")
    return text


def load_config() -> Config:
    load_dotenv()

    bot_token = os.getenv("BOT_TOKEN", "").strip()
    chat_id_raw = os.getenv("DISCUSSION_CHAT_ID", "").strip()

    missing = [
        name
        for name, value in (
            ("BOT_TOKEN", bot_token),
            ("DISCUSSION_CHAT_ID", chat_id_raw),
        )
        if not value
    ]
    if missing:
        raise SystemExit(
            f"Missing required environment variables: {', '.join(missing)}. "
            "Copy .env.example to .env and fill in the values."
        )

    try:
        discussion_chat_id = int(chat_id_raw)
    except ValueError as exc:
        raise SystemExit(
            f"DISCUSSION_CHAT_ID must be an integer, got: {chat_id_raw!r}"
        ) from exc

    return Config(
        bot_token=bot_token,
        discussion_chat_id=discussion_chat_id,
        comment_text=_load_comment_text(),
    )