from dataclasses import dataclass
from io import BytesIO

from fastapi import HTTPException, UploadFile
from PIL import Image, UnidentifiedImageError


MAX_IMAGE_SIDE = 1600
JPEG_QUALITY = 80
JPEG_MIME_TYPE = "image/jpeg"


@dataclass(slots=True)
class ProcessedImage:
    blob: bytes
    mime_type: str
    width: int
    height: int


def process_upload(file: UploadFile | None) -> ProcessedImage | None:
    if file is None or not file.filename:
        return None

    try:
        raw_bytes = file.file.read()
        if not raw_bytes:
            raise HTTPException(status_code=400, detail="上传的图片内容为空")

        with Image.open(BytesIO(raw_bytes)) as source_image:
            processed_image = _prepare_image(source_image)
    except UnidentifiedImageError as exc:
        raise HTTPException(status_code=400, detail="上传的文件不是合法图片") from exc
    except HTTPException:
        raise
    except Exception as exc:
        raise HTTPException(status_code=400, detail="图片处理失败，请尝试更换图片") from exc
    finally:
        file.file.close()

    return processed_image


def _prepare_image(source_image: Image.Image) -> ProcessedImage:
    prepared = _strip_metadata_and_convert(source_image)
    prepared.thumbnail((MAX_IMAGE_SIDE, MAX_IMAGE_SIDE))

    output = BytesIO()
    prepared.save(output, format="JPEG", quality=JPEG_QUALITY, optimize=True)
    blob = output.getvalue()

    return ProcessedImage(
        blob=blob,
        mime_type=JPEG_MIME_TYPE,
        width=prepared.width,
        height=prepared.height,
    )


def _strip_metadata_and_convert(source_image: Image.Image) -> Image.Image:
    if source_image.mode in ("RGBA", "LA"):
        background = Image.new("RGB", source_image.size, (255, 255, 255))
        alpha = source_image.getchannel("A")
        background.paste(source_image.convert("RGBA"), mask=alpha)
        return background

    if source_image.mode == "P":
        return source_image.convert("RGB")

    if source_image.mode != "RGB":
        return source_image.convert("RGB")

    return source_image.copy()