from __future__ import annotations

import numpy as np

from .deps import require_cv2
from .settings import TrimapSettings


def radius_from_ratio(shape: tuple[int, int], ratio: float, minimum: int) -> int:
    return max(minimum, int(round(max(shape) * ratio)))


def elliptical_kernel(radius: int) -> np.ndarray:
    cv2 = require_cv2()
    size = radius * 2 + 1
    return cv2.getStructuringElement(cv2.MORPH_ELLIPSE, (size, size))


def generate_trimap(
    bg_confidence: np.ndarray, settings: TrimapSettings
) -> tuple[np.ndarray, dict[str, int]]:
    cv2 = require_cv2()
    shape = bg_confidence.shape
    unknown_radius = radius_from_ratio(
        shape, settings.unknown_radius_ratio, settings.min_unknown_radius
    )
    fg_safe_radius = radius_from_ratio(
        shape, settings.fg_safe_radius_ratio, settings.min_fg_safe_radius
    )

    sure_bg = bg_confidence >= settings.sure_bg_threshold
    low_bg = bg_confidence <= settings.sure_fg_threshold

    bg_u8 = sure_bg.astype(np.uint8)
    unknown_band = cv2.dilate(bg_u8, elliptical_kernel(unknown_radius)).astype(bool)
    fg_safe = ~cv2.dilate(bg_u8, elliptical_kernel(fg_safe_radius)).astype(bool)
    sure_fg = low_bg & fg_safe

    trimap = np.full(shape, 128, dtype=np.uint8)
    trimap[sure_bg] = 0
    trimap[sure_fg] = 255

    # Keep a protective unknown band around all sure background, including holes.
    trimap[unknown_band & ~sure_bg & ~sure_fg] = 128

    stats = {
        "sure_bg_pixels": int((trimap == 0).sum()),
        "unknown_pixels": int((trimap == 128).sum()),
        "sure_fg_pixels": int((trimap == 255).sum()),
        "unknown_radius": int(unknown_radius),
        "fg_safe_radius": int(fg_safe_radius),
    }
    return trimap, stats


def trimap_to_alpha_seed(trimap: np.ndarray, bg_confidence: np.ndarray) -> np.ndarray:
    alpha = np.clip(1.0 - bg_confidence, 0.0, 1.0).astype(np.float32)
    alpha[trimap == 0] = 0.0
    alpha[trimap == 255] = 1.0
    return alpha