"""RGBA 합성 및 배경 처리 유틸."""
import numpy as np
from PIL import Image, ImageFilter


def feather_alpha(alpha: np.ndarray, amount: float) -> np.ndarray:
    """경계 부드럽게 (amount: 픽셀 반경)."""
    if amount <= 0:
        return alpha
    img = Image.fromarray((np.clip(alpha, 0, 1) * 255).astype("uint8"))
    img = img.filter(ImageFilter.GaussianBlur(radius=float(amount)))
    return np.asarray(img, dtype="float32") / 255.0


def apply_gamma(alpha: np.ndarray, gamma: float) -> np.ndarray:
    """알파 대비 조정 (gamma<1: 전경 확장, >1: 수축)."""
    if abs(gamma - 1.0) < 1e-3:
        return alpha
    return np.clip(np.power(np.clip(alpha, 0, 1), gamma), 0, 1)


def to_rgba(fg_rgb01: np.ndarray, alpha: np.ndarray) -> Image.Image:
    rgb = (np.clip(fg_rgb01, 0, 1) * 255).astype("uint8")
    a = (np.clip(alpha, 0, 1) * 255).astype("uint8")
    rgba = np.dstack([rgb, a])
    return Image.fromarray(rgba, "RGBA")


def composite_color(fg_rgb01: np.ndarray, alpha: np.ndarray, color=(255, 255, 255)) -> Image.Image:
    a = np.clip(alpha, 0, 1)[..., None]
    bg = np.array(color, dtype="float32") / 255.0
    out = fg_rgb01 * a + bg * (1 - a)
    return Image.fromarray((np.clip(out, 0, 1) * 255).astype("uint8"), "RGB")