import os
from dataclasses import dataclass
from functools import lru_cache
from dotenv import load_dotenv

load_dotenv()


def _get_bool(name: str, default: bool) -> bool:
    value = os.getenv(name)
    if value is None:
        return default

    return value.strip().lower() in {"1", "true", "yes", "on"}


def _get_int(name: str, default: int) -> int:
    """从环境变量中读取整数配置。"""
    value = os.getenv(name)
    if value is None:
        return default

    try:
        return int(value)
    except ValueError:
        return default


def _get_float(name: str, default: float) -> float:
    """从环境变量中读取浮点数配置。"""
    value = os.getenv(name)
    if value is None:
        return default

    try:
        return float(value)
    except ValueError:
        return default


@dataclass(frozen=True)
class AppSettings:
    """
    FastAPI 服务本身的运行配置。
    """

    title: str
    version: str
    description: str
    host: str
    port: int

    @classmethod
    def from_env(cls) -> "AppSettings":
        return cls(
            title=os.getenv("APP_TITLE", "Raspberry Pi Camera API"),
            version=os.getenv("APP_VERSION", "0.1.0"),
            description=os.getenv(
                "APP_DESCRIPTION",
                "用于树莓派相机抓拍的 FastAPI 服务。",
            ),
            host=os.getenv("APP_HOST", "0.0.0.0"),
            port=_get_int("APP_PORT", 8002)
        )


@dataclass(frozen=True)
class CameraSettings:
    """
    树莓派相机的集中配置。
    """

    camera_index: int
    width: int
    height: int
    frame_format: str
    jpeg_quality: int
    warmup_seconds: float
    enable_continuous_autofocus: bool
    enable_auto_white_balance: bool

    @classmethod
    def from_env(cls) -> "CameraSettings":
        return cls(
            camera_index=_get_int("CAMERA_INDEX", 0),
            width=_get_int("CAMERA_WIDTH", 2048),
            height=_get_int("CAMERA_HEIGHT", 2048),
            frame_format=os.getenv("CAMERA_FRAME_FORMAT", "RGB888"),
            jpeg_quality=_get_int("CAMERA_JPEG_QUALITY", 95),
            warmup_seconds=_get_float("CAMERA_WARMUP_SECONDS", 0.05),
            enable_continuous_autofocus=_get_bool(
                "CAMERA_ENABLE_CONTINUOUS_AUTOFOCUS",
                True,
            ),
            enable_auto_white_balance=_get_bool(
                "CAMERA_ENABLE_AUTO_WHITE_BALANCE",
                True,
            ),
        )


@dataclass(frozen=True)
class Settings:
    """项目总配置入口，统一汇总服务配置与相机配置。"""

    app: AppSettings
    camera: CameraSettings


@lru_cache(maxsize=1)
def get_settings() -> Settings:
    """
    返回单例配置对象。

    使用缓存的原因是：
    1. 避免每次请求都重复读取环境变量。
    2. 让整个项目里的配置来源保持一致。
    """
    return Settings(
        app=AppSettings.from_env(),
        camera=CameraSettings.from_env(),
    )

settings = get_settings()