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app/core/config.py

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+"""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()