import io
from pathlib import Path

from PIL import Image, ImageOps

from .base import ImageAttachment


INLINE_IMAGE_MAX_BYTES = 2_000_000
PREVIEW_TARGET_BYTES = 1_900_000
WECOM_FILE_MAX_BYTES = 20_000_000
TELEGRAM_PHOTO_MAX_BYTES = 10_000_000
TELEGRAM_FILE_MAX_BYTES = 50_000_000


def compressed_preview(image: ImageAttachment) -> ImageAttachment:
    if len(image.data) <= INLINE_IMAGE_MAX_BYTES:
        return image

    with Image.open(io.BytesIO(image.data)) as source:
        source.load()
        working = ImageOps.exif_transpose(source)
        if working.mode in {"RGBA", "LA"}:
            background = Image.new("RGB", working.size, "white")
            alpha = working.getchannel("A")
            background.paste(working.convert("RGB"), mask=alpha)
            working = background
        elif working.mode != "RGB":
            working = working.convert("RGB")

        current = working
        while True:
            for quality in (90, 82, 74, 66, 58, 50, 42, 34):
                output = io.BytesIO()
                current.save(
                    output,
                    format="JPEG",
                    quality=quality,
                    optimize=True,
                    progressive=True,
                )
                data = output.getvalue()
                if len(data) <= PREVIEW_TARGET_BYTES:
                    name = f"{Path(image.filename).stem}-preview.jpg"
                    return ImageAttachment(name, "image/jpeg", data)
            width, height = current.size
            if min(width, height) <= 128:
                raise RuntimeError("image cannot be compressed below preview limit")
            current = current.resize(
                (max(1, int(width * 0.8)), max(1, int(height * 0.8))),
                Image.Resampling.LANCZOS,
            )