import numpy as np
from PIL import Image

def get_bbox_from_alpha(rgba: Image.Image):
    arr = np.array(rgba)
    alpha = arr[...,3]
    ys, xs = np.where(alpha>0)
    if ys.size == 0:
        return None
    x1, x2 = xs.min(), xs.max()
    y1, y2 = ys.min(), ys.max()
    return x1, y1, x2, y2

def paste_with_alpha(bg: np.ndarray, src: np.ndarray, offset: tuple[int,int]) -> Image.Image:
    res = bg.copy()
    x, y = offset
    h, w = src.shape[:2]
    x1, y1 = max(x,0), max(y,0)
    x2 = min(x+w, bg.shape[1])
    y2 = min(y+h, bg.shape[0])
    if x1>=x2 or y1>=y2:
        return Image.fromarray(res)
    cs = src[y1-y:y2-y, x1-x:x2-x]
    cd = res[y1:y2, x1:x2]
    mask = cs[...,3]>0
    if cd.shape[2]==3:
        cd[mask] = cs[mask][..., :3]
    else:
        cd[mask] = cs[mask]
    res[y1:y2, x1:x2] = cd
    return Image.fromarray(res)