from __future__ import annotations

import base64
import io

from PIL import Image, ImageDraw


def b64_to_pil_image(b64: str) -> Image.Image:
    raw = base64.b64decode(b64)
    return Image.open(io.BytesIO(raw))


def pil_image_to_png_b64(img: Image.Image) -> str:
    buf = io.BytesIO()
    img.save(buf, format="PNG")
    return base64.b64encode(buf.getvalue()).decode("ascii")


def default_half_mask(img: Image.Image) -> Image.Image:
    w, h = img.size
    mask = Image.new("L", (w, h), 0)
    draw = ImageDraw.Draw(mask)
    draw.rectangle([w // 2, 0, w, h], fill=255)
    return mask