"""Application settings — single source of truth, sourced from environment.

Nothing is hardcoded. All knobs come from env vars (or a local ``.env`` during
development). Access the cached singleton via :func:`get_settings`.
"""

from functools import lru_cache
from pathlib import Path
from typing import Literal

from pydantic import Field, SecretStr, field_validator
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        extra="ignore",
        case_sensitive=False,
    )

    # -- runtime ----------------------------------------------------------
    environment: Literal["dev", "test", "prod"] = "dev"
    log_level: str = "INFO"
    log_json: bool = Field(
        default=False,
        description="Structured JSON logs (enable in prod).",
    )

    # -- database ---------------------------------------------------------
    # Async driver required (asyncpg). Example:
    # postgresql+asyncpg://mcma:mcma@db:5432/mcma
    database_url: str = "postgresql+asyncpg://mcma:mcma@localhost:5432/mcma"
    db_echo: bool = False
    db_pool_size: int = 5
    db_max_overflow: int = 10

    # -- redis (cache + arq broker) --------------------------------------
    redis_url: str = "redis://localhost:6379/0"

    # -- auth -------------------------------------------------------------
    jwt_secret: SecretStr = SecretStr("change-me-in-prod")
    jwt_algorithm: str = "HS256"
    access_token_ttl_seconds: int = 60 * 15  # 15 min
    refresh_token_ttl_seconds: int = 60 * 60 * 24 * 30  # 30 days (offline-first)

    # -- media / storage --------------------------------------------------
    media_path: Path = Path("/data/media")
    transcode_cache_path: Path = Path("/data/transcode-cache")
    max_parallel_downloads: int = 2

    # -- external services (all optional; graceful degradation) ----------
    ml_service_url: str | None = None
    acoustid_api_key: SecretStr | None = None
    musicbrainz_user_agent: str = "mcma-backend/0.1.0 ( https://github.com/your/repo )"
    youtube_cookies_path: Path | None = None

    @field_validator("database_url")
    @classmethod
    def _require_async_driver(cls, v: str) -> str:
        if "+asyncpg" not in v:
            raise ValueError("database_url must use the asyncpg driver: postgresql+asyncpg://")
        return v

    @property
    def is_prod(self) -> bool:
        return self.environment == "prod"


@lru_cache
def get_settings() -> Settings:
    """Cached settings singleton. Patch the cache in tests via ``get_settings.cache_clear()``."""
    return Settings()