"""Runtime settings, read from environment variables (and an optional .env file)."""

from __future__ import annotations

import os
from dataclasses import dataclass
from pathlib import Path

from dotenv import load_dotenv

PROJECT_ROOT = Path(__file__).resolve().parent.parent

DEFAULT_BASE_URL = "https://api.devupai.com/v1"
DEFAULT_MODEL = "deepseek-ai/DeepSeek-V4.1-Flash-1017"


class ConfigError(RuntimeError):
    """Raised when a required setting is missing or invalid."""


def _int_env(name: str, default: int, minimum: int = 1) -> int:
    raw = os.getenv(name)
    if raw is None or raw.strip() == "":
        return default
    try:
        value = int(raw)
    except ValueError as exc:
        raise ConfigError(f"{name} must be an integer, got {raw!r}") from exc
    if value < minimum:
        raise ConfigError(f"{name} must be >= {minimum}, got {value}")
    return value


@dataclass(frozen=True)
class Settings:
    devup_api_key: str
    devup_base_url: str
    model: str
    telegram_bot_token: str | None
    admin_chat_id: int | None
    db_path: Path
    catalog_path: Path
    history_messages: int
    rate_limit_per_minute: int
    max_input_chars: int
    max_tool_rounds: int
    max_output_tokens: int
    request_timeout_s: int

    @classmethod
    def from_env(cls, *, require_api_key: bool = True, require_telegram: bool = False) -> Settings:
        load_dotenv(PROJECT_ROOT / ".env")

        api_key = os.getenv("DEVUP_API_KEY", "").strip()
        if require_api_key and not api_key:
            raise ConfigError("DEVUP_API_KEY is not set. Copy .env.example to .env and add your key.")

        token = os.getenv("TELEGRAM_BOT_TOKEN", "").strip() or None
        if require_telegram and not token:
            raise ConfigError("TELEGRAM_BOT_TOKEN is not set. Create a bot with @BotFather and add its token to .env.")

        admin_raw = os.getenv("ADMIN_CHAT_ID", "").strip()
        try:
            admin_chat_id = int(admin_raw) if admin_raw else None
        except ValueError as exc:
            raise ConfigError(f"ADMIN_CHAT_ID must be a numeric Telegram chat id, got {admin_raw!r}") from exc

        return cls(
            devup_api_key=api_key,
            devup_base_url=os.getenv("DEVUP_BASE_URL", DEFAULT_BASE_URL).strip() or DEFAULT_BASE_URL,
            model=os.getenv("DEVUP_MODEL", DEFAULT_MODEL).strip() or DEFAULT_MODEL,
            telegram_bot_token=token,
            admin_chat_id=admin_chat_id,
            db_path=Path(os.getenv("STORE_DB_PATH", str(PROJECT_ROOT / "data" / "store.db"))),
            catalog_path=Path(os.getenv("STORE_CATALOG_PATH", str(PROJECT_ROOT / "data" / "demo_store.json"))),
            history_messages=_int_env("HISTORY_MESSAGES", 12),
            rate_limit_per_minute=_int_env("RATE_LIMIT_PER_MINUTE", 8),
            max_input_chars=_int_env("MAX_INPUT_CHARS", 1000),
            max_tool_rounds=_int_env("MAX_TOOL_ROUNDS", 4),
            max_output_tokens=_int_env("MAX_OUTPUT_TOKENS", 8192),
            request_timeout_s=_int_env("REQUEST_TIMEOUT_S", 60),
        )