main.py

from typing import Optional
from pydantic import Field, validator
from pydantic_settings import BaseSettings
from functools import lru_cache


class Settings(BaseSettings):
    """
    Application configuration using Pydantic BaseSettings.
    
    Environment variables can override these defaults.
    Configuration is loaded from .env file if present.
    """
    
    # Application settings
    app_name: str = Field(default="AstroML Dashboard API", env="APP_NAME")
    app_version: str = Field(default="1.0.0", env="APP_VERSION")
    debug: bool = Field(default=False, env="DEBUG")
    
    # Server settings
    host: str = Field(default="0.0.0.0", env="HOST")
    port: int = Field(default=8000, env="PORT")
    
    # Database settings
    database_url: str = Field(
        default="sqlite:///./astroml.db",
        env="DATABASE_URL",
        description="Database connection URL"
    )
    database_pool_size: int = Field(default=10, env="DATABASE_POOL_SIZE")
    database_max_overflow: int = Field(default=20, env="DATABASE_MAX_OVERFLOW")
    
    # API settings
    api_key: Optional[str] = Field(default=None, env="API_KEY")
    api_key_name: str = Field(default="X-API-Key", env="API_KEY_NAME")
    
    # CORS settings
    allowed_origins: list[str] = Field(
        default=["http://localhost:5173", "http://localhost:3000"],
        env="ALLOWED_ORIGINS"
    )
    cors_allow_credentials: bool = Field(default=True, env="CORS_ALLOW_CREDENTIALS")
    cors_allow_methods: list[str] = Field(
        default=["*"],
        env="CORS_ALLOW_METHODS"
    )
    cors_allow_headers: list[str] = Field(
        default=["*"],
        env="CORS_ALLOW_HEADERS"
    )
    
    # Security settings
    secret_key: str = Field(
        default="your-secret-key-change-in-production",
        env="SECRET_KEY"
    )
    algorithm: str = Field(default="HS256", env="ALGORITHM")
    access_token_expire_minutes: int = Field(
        default=30,
        env="ACCESS_TOKEN_EXPIRE_MINUTES"
    )
    
    # Logging settings
    log_level: str = Field(default="INFO", env="LOG_LEVEL")
    log_format: str = Field(
        default="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
        env="LOG_FORMAT"
    )
    
    @validator("port")
    def validate_port(cls, v: int) -> int:
        """Validate port number is in valid range."""
        if not 1024 <= v <= 65535:
            raise ValueError(f"Port {v} is not in valid range (1024-65535)")
        return v
    
    @validator("log_level")
    def validate_log_level(cls, v: str) -> str:
        """Validate log level is valid."""
        valid_levels = ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
        if v.upper() not in valid_levels:
            raise ValueError(f"Invalid log level: {v}. Must be one of {valid_levels}")
        return v.upper()
    
    class Config:
        """Pydantic configuration."""
        env_file = ".env"
        env_file_encoding = "utf-8"
        case_sensitive = False


@lru_cache()
def get_settings() -> Settings:
    """
    Get cached settings instance.
    
    Returns:
        Settings: Application settings instance
    """
    return Settings()