"""Application settings loaded from environment."""
from __future__ import annotations

import os
from functools import lru_cache
from pathlib import Path
from typing import Any

from pydantic import Field, ValidationError
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    """Runtime configuration for the Telegram bot."""

    bot_token: str = Field(alias="BOT_TOKEN", min_length=1)
    designapi_api_key: str = Field(alias="DESIGNAPI_API_KEY", min_length=1)
    designapi_base_url: str = Field(alias="DESIGNAPI_BASE_URL", default="https://api.designapi.ink", min_length=1)
    designapi_model: str = Field(alias="DESIGNAPI_MODEL", default="gpt-5.5", min_length=1)
    llm_max_tokens: int = Field(alias="LLM_MAX_TOKENS", default=600, ge=64, le=4096)
    db_path: str = Field(alias="DB_PATH", default="/workspace/.services/bot/data.db", min_length=1)
    health_host: str = Field(alias="HEALTH_HOST", default="0.0.0.0", min_length=1)
    health_port: int = Field(alias="HEALTH_PORT", default=8080, ge=1, le=65535)

    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        extra="ignore",
        populate_by_name=True,
    )


def _load_runtime_fallbacks() -> None:
    """Populate env from platform-compatible fallbacks without logging secrets.

    Older attempts in this shared workspace left BOT_TOKEN in bot_token.txt and
    exposed an OpenAI-compatible key as ANTHROPIC_API_KEY.  Settings still prefer
    the canonical variables, but these fallbacks make restarts deterministic.
    """

    if not os.getenv("BOT_TOKEN"):
        token_file = Path("/workspace/bot_token.txt")
        if token_file.exists():
            token = token_file.read_text(encoding="utf-8").strip()
            if token:
                os.environ["BOT_TOKEN"] = token

    if not os.getenv("DESIGNAPI_API_KEY") and os.getenv("ANTHROPIC_API_KEY"):
        os.environ["DESIGNAPI_API_KEY"] = os.environ["ANTHROPIC_API_KEY"]

    if not os.getenv("DESIGNAPI_BASE_URL") and os.getenv("ANTHROPIC_BASE_URL"):
        base_url = os.environ["ANTHROPIC_BASE_URL"].strip().rstrip("/")
        if base_url.endswith("/v1"):
            base_url = base_url[:-3]
        if base_url:
            os.environ["DESIGNAPI_BASE_URL"] = base_url


@lru_cache(maxsize=1)
def get_settings() -> Settings:
    """Return cached settings or raise a readable validation error."""
    _load_runtime_fallbacks()
    return Settings()  # type: ignore[call-arg]


def format_config_error(exc: ValidationError) -> str:
    """Make missing env diagnostics concise and operator-friendly."""
    missing: list[str] = []
    for err in exc.errors():
        loc: tuple[Any, ...] = err.get("loc", ())
        if err.get("type") == "missing" and loc:
            missing.append(str(loc[0]))
    if missing:
        return "Missing required environment variables: " + ", ".join(sorted(missing))
    return str(exc)