"""
Advanced image processing operations.

This module provides advanced image processing techniques including:
- Frequency domain operations (FFT, filters)
- Texture analysis (Gabor, LBP, GLCM)
- Color space transformations
- Advanced enhancement (Gamma, Retinex)
- Feature extraction (HOG, corners)
- Morphological extensions (skeletonization, distance transform)
- Image segmentation
"""

from enum import Enum
from typing import Optional, Tuple, Union

import cv2
import numpy as np
from numpy.typing import NDArray

from pyimgano.utils.optional_deps import require

SKIMAGE_FILTERS_MODULE = "skimage.filters"
SKIMAGE_FEATURE_MODULE = "skimage.feature"
SKIMAGE_MORPHOLOGY_MODULE = "skimage.morphology"


# Enums for type-safe operation selection


class ColorSpace(Enum):
    """Color space options."""

    RGB = "rgb"
    BGR = "bgr"
    HSV = "hsv"
    LAB = "lab"
    YCrCb = "ycrcb"
    GRAY = "gray"
    HLS = "hls"
    LUV = "luv"


class ThresholdMethod(Enum):
    """Thresholding methods."""

    OTSU = "otsu"
    ADAPTIVE_MEAN = "adaptive_mean"
    ADAPTIVE_GAUSSIAN = "adaptive_gaussian"
    TRIANGLE = "triangle"
    YEN = "yen"
    ISODATA = "isodata"


class CornerDetector(Enum):
    """Corner detection methods."""

    HARRIS = "harris"
    SHI_TOMASI = "shi_tomasi"
    FAST = "fast"
    GOOD_FEATURES = "good_features"


class MorphologicalAdvanced(Enum):
    """Advanced morphological operations."""

    SKELETON = "skeleton"
    THIN = "thin"
    CONVEX_HULL = "convex_hull"
    DISTANCE_TRANSFORM = "distance_transform"


# Frequency Domain Operations


def apply_fft(image: NDArray) -> Tuple[NDArray, NDArray]:
    """
    Apply Fast Fourier Transform to image.

    Args:
        image: Input image (grayscale)

    Returns:
        Tuple of (magnitude_spectrum, phase_spectrum)
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    # Apply FFT
    f = np.fft.fft2(image)
    fshift = np.fft.fftshift(f)

    # Get magnitude and phase
    magnitude = np.abs(fshift)
    phase = np.angle(fshift)

    return magnitude, phase


def apply_ifft(magnitude: NDArray, phase: NDArray) -> NDArray:
    """
    Apply Inverse Fast Fourier Transform.

    Args:
        magnitude: Magnitude spectrum
        phase: Phase spectrum

    Returns:
        Reconstructed image
    """
    # Reconstruct complex spectrum
    fshift = magnitude * np.exp(1j * phase)
    f = np.fft.ifftshift(fshift)

    # Apply inverse FFT
    img_back = np.fft.ifft2(f)
    img_back = np.abs(img_back)

    return img_back.astype(np.uint8)


def frequency_filter(
    image: NDArray, filter_type: str = "lowpass", cutoff_frequency: float = 30.0
) -> NDArray:
    """
    Apply frequency domain filter.

    Args:
        image: Input image
        filter_type: 'lowpass', 'highpass', 'bandpass', 'bandstop'
        cutoff_frequency: Cutoff frequency for filter

    Returns:
        Filtered image
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    rows, cols = image.shape
    crow, ccol = rows // 2, cols // 2

    # Apply FFT
    f = np.fft.fft2(image)
    fshift = np.fft.fftshift(f)

    # Create mask (vectorized)
    ft = str(filter_type).strip().lower()
    cutoff = float(cutoff_frequency)
    if cutoff <= 0:
        raise ValueError(f"cutoff_frequency must be > 0, got {cutoff_frequency}")

    y, x = np.ogrid[:rows, :cols]
    dist = np.sqrt((y - crow) ** 2 + (x - ccol) ** 2)

    if ft == "lowpass":
        mask = (dist <= cutoff).astype(np.float32)
    elif ft == "highpass":
        mask = (dist > cutoff).astype(np.float32)
    elif ft == "bandpass":
        hi = cutoff * 2.0
        mask = ((dist >= cutoff) & (dist <= hi)).astype(np.float32)
    elif ft == "bandstop":
        hi = cutoff * 2.0
        mask = ((dist < cutoff) | (dist > hi)).astype(np.float32)
    else:
        raise ValueError(
            "filter_type must be one of: lowpass, highpass, bandpass, bandstop. "
            f"Got: {filter_type!r}"
        )

    # Apply mask
    fshift = fshift * mask

    # Inverse FFT
    f_ishift = np.fft.ifftshift(fshift)
    img_back = np.fft.ifft2(f_ishift)
    img_back = np.abs(img_back)

    return img_back.astype(np.uint8)


# Texture Analysis


def apply_gabor_filter(
    image: NDArray,
    frequency: float = 0.1,
    theta: float = 0,
    sigma_x: float = 3.0,
    sigma_y: float = 3.0,
) -> NDArray:
    """
    Apply Gabor filter for texture analysis.

    Args:
        image: Input image
        frequency: Frequency of the sinusoidal wave
        theta: Orientation in radians
        sigma_x: Standard deviation in x direction
        sigma_y: Standard deviation in y direction

    Returns:
        Filtered image (real part)
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    # Normalize image
    image = image.astype(np.float32) / 255.0

    # Apply Gabor filter
    skfilters = require(SKIMAGE_FILTERS_MODULE, extra="skimage", purpose="Gabor filter")
    real, _ = skfilters.gabor(
        image,
        frequency=frequency,
        theta=theta,
        sigma_x=sigma_x,
        sigma_y=sigma_y,
    )

    # Normalize and convert to uint8
    real = np.abs(real)
    real = (real - real.min()) / (real.max() - real.min()) * 255

    return real.astype(np.uint8)


def compute_lbp(
    image: NDArray, n_points: int = 8, radius: float = 1.0, method: str = "uniform"
) -> NDArray:
    """
    Compute Local Binary Pattern features.

    Args:
        image: Input image
        n_points: Number of circularly symmetric neighbor points
        radius: Radius of circle
        method: 'default', 'ror', 'uniform', 'var'

    Returns:
        LBP feature image
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    # Compute LBP
    skfeature = require(SKIMAGE_FEATURE_MODULE, extra="skimage", purpose="LBP texture features")
    lbp = skfeature.local_binary_pattern(image, n_points, radius, method=method)

    # Normalize to 0-255
    lbp = ((lbp - lbp.min()) / (lbp.max() - lbp.min()) * 255).astype(np.uint8)

    return lbp


def compute_glcm_features(
    image: NDArray,
    distances: Optional[list] = None,
    angles: Optional[list] = None,
) -> dict:
    """
    Compute Gray-Level Co-occurrence Matrix features.

    Args:
        image: Input image
        distances: List of pixel pair distances
        angles: List of pixel pair angles

    Returns:
        Dictionary of GLCM features (contrast, dissimilarity, homogeneity, energy, correlation)
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    distances = [1] if distances is None else list(distances)
    angles = [0, np.pi / 4, np.pi / 2, 3 * np.pi / 4] if angles is None else list(angles)

    skfeature = require(SKIMAGE_FEATURE_MODULE, extra="skimage", purpose="GLCM texture features")
    greycomatrix = getattr(skfeature, "graycomatrix", None) or getattr(
        skfeature, "greycomatrix", None
    )
    greycoprops = getattr(skfeature, "graycoprops", None) or getattr(skfeature, "greycoprops", None)
    if greycomatrix is None or greycoprops is None:  # pragma: no cover - version mismatch
        raise RuntimeError(
            "Installed scikit-image does not provide graycomatrix/greycoprops. "
            "Please upgrade scikit-image (pyimgano[skimage])."
        )

    # Compute GLCM
    glcm = greycomatrix(
        image, distances=distances, angles=angles, levels=256, symmetric=True, normed=True
    )

    # Compute properties
    features = {
        "contrast": greycoprops(glcm, "contrast").mean(),
        "dissimilarity": greycoprops(glcm, "dissimilarity").mean(),
        "homogeneity": greycoprops(glcm, "homogeneity").mean(),
        "energy": greycoprops(glcm, "energy").mean(),
        "correlation": greycoprops(glcm, "correlation").mean(),
    }

    return features


# Color Space Operations


def convert_color_space(
    image: NDArray, from_space: Union[str, ColorSpace], to_space: Union[str, ColorSpace]
) -> NDArray:
    """
    Convert image between color spaces.

    Args:
        image: Input image
        from_space: Source color space
        to_space: Target color space

    Returns:
        Converted image
    """
    if isinstance(from_space, str):
        from_space = ColorSpace(from_space.lower())
    if isinstance(to_space, str):
        to_space = ColorSpace(to_space.lower())

    # Mapping of color space conversions
    conversions = {
        (ColorSpace.BGR, ColorSpace.RGB): cv2.COLOR_BGR2RGB,
        (ColorSpace.BGR, ColorSpace.HSV): cv2.COLOR_BGR2HSV,
        (ColorSpace.BGR, ColorSpace.LAB): cv2.COLOR_BGR2LAB,
        (ColorSpace.BGR, ColorSpace.YCrCb): cv2.COLOR_BGR2YCrCb,
        (ColorSpace.BGR, ColorSpace.GRAY): cv2.COLOR_BGR2GRAY,
        (ColorSpace.BGR, ColorSpace.HLS): cv2.COLOR_BGR2HLS,
        (ColorSpace.BGR, ColorSpace.LUV): cv2.COLOR_BGR2LUV,
        (ColorSpace.RGB, ColorSpace.BGR): cv2.COLOR_RGB2BGR,
        (ColorSpace.RGB, ColorSpace.HSV): cv2.COLOR_RGB2HSV,
        (ColorSpace.RGB, ColorSpace.LAB): cv2.COLOR_RGB2LAB,
        (ColorSpace.RGB, ColorSpace.GRAY): cv2.COLOR_RGB2GRAY,
        (ColorSpace.HSV, ColorSpace.BGR): cv2.COLOR_HSV2BGR,
        (ColorSpace.HSV, ColorSpace.RGB): cv2.COLOR_HSV2RGB,
        (ColorSpace.LAB, ColorSpace.BGR): cv2.COLOR_LAB2BGR,
        (ColorSpace.LAB, ColorSpace.RGB): cv2.COLOR_LAB2RGB,
        (ColorSpace.GRAY, ColorSpace.BGR): cv2.COLOR_GRAY2BGR,
        (ColorSpace.GRAY, ColorSpace.RGB): cv2.COLOR_GRAY2RGB,
    }

    key = (from_space, to_space)
    if key in conversions:
        return cv2.cvtColor(image, conversions[key])
    else:
        raise ValueError(f"Conversion from {from_space} to {to_space} not supported")


def equalize_color_histogram(image: NDArray, method: str = "hsv") -> NDArray:
    """
    Equalize histogram in color space.

    Args:
        image: Input color image
        method: 'hsv' (equalize V), 'lab' (equalize L), 'ycrcb' (equalize Y)

    Returns:
        Histogram equalized image
    """
    if method == "hsv":
        hsv = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)
        hsv[:, :, 2] = cv2.equalizeHist(hsv[:, :, 2])
        return cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR)

    elif method == "lab":
        lab = cv2.cvtColor(image, cv2.COLOR_BGR2LAB)
        lab[:, :, 0] = cv2.equalizeHist(lab[:, :, 0])
        return cv2.cvtColor(lab, cv2.COLOR_LAB2BGR)

    elif method == "ycrcb":
        ycrcb = cv2.cvtColor(image, cv2.COLOR_BGR2YCrCb)
        ycrcb[:, :, 0] = cv2.equalizeHist(ycrcb[:, :, 0])
        return cv2.cvtColor(ycrcb, cv2.COLOR_YCrCb2BGR)

    else:
        raise ValueError(f"Unknown method: {method}")


# Advanced Enhancement


def gamma_correction(image: NDArray, gamma: float = 1.0) -> NDArray:
    """
    Apply gamma correction.

    Args:
        image: Input image
        gamma: Gamma value (< 1: brighter, > 1: darker)

    Returns:
        Gamma corrected image
    """
    # Build lookup table
    inv_gamma = 1.0 / gamma
    table = np.array([((i / 255.0) ** inv_gamma) * 255 for i in np.arange(0, 256)]).astype("uint8")

    # Apply gamma correction
    return cv2.LUT(image, table)


def contrast_stretching(
    image: NDArray, lower_percentile: float = 2, upper_percentile: float = 98
) -> NDArray:
    """
    Apply contrast stretching.

    Args:
        image: Input image
        lower_percentile: Lower percentile for stretching
        upper_percentile: Upper percentile for stretching

    Returns:
        Contrast stretched image
    """
    if len(image.shape) == 3:
        # Process each channel separately
        result = np.zeros_like(image)
        for i in range(3):
            channel = image[:, :, i]
            p_low = np.percentile(channel, lower_percentile)
            p_high = np.percentile(channel, upper_percentile)
            result[:, :, i] = np.clip((channel - p_low) * 255.0 / (p_high - p_low), 0, 255)
        return result.astype(np.uint8)
    else:
        p_low = np.percentile(image, lower_percentile)
        p_high = np.percentile(image, upper_percentile)
        return np.clip((image - p_low) * 255.0 / (p_high - p_low), 0, 255).astype(np.uint8)


def retinex_ssr(image: NDArray, sigma: float = 15.0) -> NDArray:
    """
    Single-Scale Retinex for illumination invariant processing.

    Args:
        image: Input image
        sigma: Gaussian kernel sigma

    Returns:
        Retinex enhanced image
    """
    if len(image.shape) == 3:
        # Process each channel separately
        result = np.zeros_like(image, dtype=np.float32)
        for i in range(3):
            channel = image[:, :, i].astype(np.float32) + 1.0  # Add 1 to avoid log(0)
            gaussian = cv2.GaussianBlur(channel, (0, 0), sigma)
            retinex = np.log10(channel) - np.log10(gaussian)
            result[:, :, i] = retinex

        # Normalize
        result = (result - result.min()) / (result.max() - result.min()) * 255
        return result.astype(np.uint8)
    else:
        image_float = image.astype(np.float32) + 1.0
        gaussian = cv2.GaussianBlur(image_float, (0, 0), sigma)
        retinex = np.log10(image_float) - np.log10(gaussian)
        retinex = (retinex - retinex.min()) / (retinex.max() - retinex.min()) * 255
        return retinex.astype(np.uint8)


def retinex_msr(image: NDArray, sigmas: Optional[list] = None) -> NDArray:
    """
    Multi-Scale Retinex for illumination invariant processing.

    Args:
        image: Input image
        sigmas: List of Gaussian kernel sigmas

    Returns:
        Retinex enhanced image
    """
    sigmas = list(sigmas or [15, 80, 250])

    result = np.zeros_like(image, dtype=np.float32)

    for sigma in sigmas:
        ssr = retinex_ssr(image, sigma).astype(np.float32)
        result += ssr

    result = result / len(sigmas)
    result = (result - result.min()) / (result.max() - result.min()) * 255

    return result.astype(np.uint8)


# Denoising


def non_local_means_denoising(
    image: NDArray, h: float = 10, template_window_size: int = 7, search_window_size: int = 21
) -> NDArray:
    """
    Apply non-local means denoising.

    Args:
        image: Input image
        h: Filter strength
        template_window_size: Size of template patch
        search_window_size: Size of search area

    Returns:
        Denoised image
    """
    if len(image.shape) == 3:
        return cv2.fastNlMeansDenoisingColored(
            image, None, h, h, template_window_size, search_window_size
        )
    else:
        return cv2.fastNlMeansDenoising(image, None, h, template_window_size, search_window_size)


def anisotropic_diffusion(
    image: NDArray, niter: int = 10, kappa: float = 50, gamma: float = 0.1, option: int = 1
) -> NDArray:
    """
    Apply anisotropic diffusion for edge-preserving smoothing.

    Args:
        image: Input image
        niter: Number of iterations
        kappa: Conduction coefficient
        gamma: Integration constant (0 < gamma <= 0.25)
        option: 1 or 2, different diffusion functions

    Returns:
        Smoothed image
    """
    # Delegate to the dedicated implementation (keeps advanced_operations lightweight).
    from pyimgano.preprocessing.anisotropic_diffusion import anisotropic_diffusion as _pm_diffusion

    return _pm_diffusion(
        image,
        niter=int(niter),
        kappa=float(kappa),
        gamma=float(gamma),
        option=int(option),
    )


# Feature Extraction


def extract_hog_features(
    image: NDArray,
    orientations: int = 9,
    pixels_per_cell: Tuple[int, int] = (8, 8),
    cells_per_block: Tuple[int, int] = (2, 2),
    visualize: bool = False,
) -> Union[NDArray, Tuple[NDArray, NDArray]]:
    """
    Extract Histogram of Oriented Gradients features.

    Args:
        image: Input image
        orientations: Number of orientation bins
        pixels_per_cell: Size of a cell
        cells_per_block: Number of cells in each block
        visualize: Return visualization image

    Returns:
        HOG features or (features, visualization)
    """
    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    skfeature = require(SKIMAGE_FEATURE_MODULE, extra="skimage", purpose="HOG feature extraction")
    hog = skfeature.hog

    if visualize:
        features, hog_image = hog(
            image,
            orientations=orientations,
            pixels_per_cell=pixels_per_cell,
            cells_per_block=cells_per_block,
            visualize=True,
        )
        # Normalize visualization
        hog_image = (hog_image * 255).astype(np.uint8)
        return features, hog_image
    else:
        features = hog(
            image,
            orientations=orientations,
            pixels_per_cell=pixels_per_cell,
            cells_per_block=cells_per_block,
            visualize=False,
        )
        return features


def detect_corners(
    image: NDArray, method: Union[str, CornerDetector] = "harris", **kwargs
) -> NDArray:
    """
    Detect corners in image.

    Args:
        image: Input image
        method: Corner detection method
        **kwargs: Method-specific parameters

    Returns:
        Corner response image or corner coordinates
    """
    if isinstance(method, str):
        method = CornerDetector(method.lower())

    if len(image.shape) == 3:
        gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    else:
        gray = image

    if method == CornerDetector.HARRIS:
        block_size = kwargs.get("block_size", 2)
        ksize = kwargs.get("ksize", 3)
        k = kwargs.get("k", 0.04)
        dst = cv2.cornerHarris(gray, block_size, ksize, k)
        return dst

    elif method == CornerDetector.SHI_TOMASI:
        max_corners = kwargs.get("max_corners", 100)
        quality_level = kwargs.get("quality_level", 0.01)
        min_distance = kwargs.get("min_distance", 10)
        corners = cv2.goodFeaturesToTrack(gray, max_corners, quality_level, min_distance)
        return corners

    elif method == CornerDetector.FAST:
        threshold = kwargs.get("threshold", 10)
        non_max_suppression = kwargs.get("non_max_suppression", True)
        fast = cv2.FastFeatureDetector_create(
            threshold=threshold, nonmaxSuppression=non_max_suppression
        )
        keypoints = fast.detect(gray, None)
        # Convert to coordinates
        corners = np.array([kp.pt for kp in keypoints], dtype=np.float32)
        return corners

    else:
        raise ValueError(f"Unknown corner detection method: {method}")


# Advanced Morphological Operations


def apply_advanced_morphology(
    image: NDArray, operation: Union[str, MorphologicalAdvanced]
) -> NDArray:
    """
    Apply advanced morphological operations.

    Args:
        image: Input binary image
        operation: Morphological operation

    Returns:
        Processed image
    """
    if isinstance(operation, str):
        operation = MorphologicalAdvanced(operation.lower())

    if len(image.shape) == 3:
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    # Ensure binary image
    _, binary = cv2.threshold(image, 127, 255, cv2.THRESH_BINARY)
    binary_bool = binary.astype(bool)

    if operation == MorphologicalAdvanced.SKELETON:
        skmorph = require(SKIMAGE_MORPHOLOGY_MODULE, extra="skimage", purpose="skeletonization")
        skeleton = skmorph.skeletonize(binary_bool)
        return (skeleton * 255).astype(np.uint8)

    elif operation == MorphologicalAdvanced.THIN:
        skmorph = require(SKIMAGE_MORPHOLOGY_MODULE, extra="skimage", purpose="thinning")
        thinned = skmorph.thin(binary_bool)
        return (thinned * 255).astype(np.uint8)

    elif operation == MorphologicalAdvanced.CONVEX_HULL:
        skmorph = require(
            SKIMAGE_MORPHOLOGY_MODULE, extra="skimage", purpose="convex hull morphology"
        )
        hull = skmorph.convex_hull_image(binary_bool)
        return (hull * 255).astype(np.uint8)

    elif operation == MorphologicalAdvanced.DISTANCE_TRANSFORM:
        dist_transform = cv2.distanceTransform(binary, cv2.DIST_L2, 5)
        # Normalize to 0-255
        dist_transform = cv2.normalize(dist_transform, None, 0, 255, cv2.NORM_MINMAX)
        return dist_transform.astype(np.uint8)

    else:
        raise ValueError(f"Unknown morphological operation: {operation}")


# Segmentation


def apply_threshold(
    image: NDArray, method: Union[str, ThresholdMethod] = "otsu", **kwargs
) -> NDArray:
    """
    Apply thresholding for segmentation.

    Args:
        image: Input image
        method: Thresholding method
        **kwargs: Method-specific parameters

    Returns:
        Binary image
    """
    if isinstance(method, str):
        method = ThresholdMethod(method.lower())

    if len(image.shape) == 3:
        gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    else:
        gray = image

    if method == ThresholdMethod.OTSU:
        _, binary = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
        return binary

    elif method == ThresholdMethod.ADAPTIVE_MEAN:
        block_size = kwargs.get("block_size", 11)
        c = kwargs.get("c", 2)
        binary = cv2.adaptiveThreshold(
            gray, 255, cv2.ADAPTIVE_THRESH_MEAN_C, cv2.THRESH_BINARY, block_size, c
        )
        return binary

    elif method == ThresholdMethod.ADAPTIVE_GAUSSIAN:
        block_size = kwargs.get("block_size", 11)
        c = kwargs.get("c", 2)
        binary = cv2.adaptiveThreshold(
            gray, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY, block_size, c
        )
        return binary

    elif method == ThresholdMethod.TRIANGLE:
        _, binary = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_TRIANGLE)
        return binary

    elif method == ThresholdMethod.YEN:
        skfilters = require(SKIMAGE_FILTERS_MODULE, extra="skimage", purpose="Yen threshold")
        threshold_value = skfilters.threshold_yen(gray)
        binary = (gray > threshold_value).astype(np.uint8) * 255
        return binary

    elif method == ThresholdMethod.ISODATA:
        skfilters = require(SKIMAGE_FILTERS_MODULE, extra="skimage", purpose="Isodata threshold")
        threshold_value = skfilters.threshold_isodata(gray)
        binary = (gray > threshold_value).astype(np.uint8) * 255
        return binary

    else:
        raise ValueError(f"Unknown thresholding method: {method}")


def watershed_segmentation(image: NDArray, markers: Optional[NDArray] = None) -> NDArray:
    """
    Apply watershed segmentation.

    Args:
        image: Input image
        markers: Marker image (if None, automatic markers are generated)

    Returns:
        Segmented image
    """
    if len(image.shape) == 2:
        image = cv2.cvtColor(image, cv2.COLOR_GRAY2BGR)

    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

    if markers is None:
        # Automatic marker generation
        _, thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)

        # Noise removal
        kernel = np.ones((3, 3), np.uint8)
        opening = cv2.morphologyEx(thresh, cv2.MORPH_OPEN, kernel, iterations=2)

        # Sure background area
        sure_bg = cv2.dilate(opening, kernel, iterations=3)

        # Finding sure foreground area
        dist_transform = cv2.distanceTransform(opening, cv2.DIST_L2, 5)
        _, sure_fg = cv2.threshold(dist_transform, 0.7 * dist_transform.max(), 255, 0)

        # Finding unknown region
        sure_fg = np.uint8(sure_fg)
        unknown = cv2.subtract(sure_bg, sure_fg)

        # Marker labelling
        _, markers = cv2.connectedComponents(sure_fg)
        markers = markers + 1
        markers[unknown == 255] = 0

    # Apply watershed
    markers = cv2.watershed(image, markers)

    # Create output image
    result = np.zeros_like(gray)
    result[markers == -1] = 255  # Boundaries

    return result


# Image Pyramids


def gaussian_pyramid(image: NDArray, levels: int = 3) -> list:
    """
    Create Gaussian pyramid.

    Args:
        image: Input image
        levels: Number of pyramid levels

    Returns:
        List of pyramid levels
    """
    pyramid = [image]

    for _ in range(levels - 1):
        image = cv2.pyrDown(image)
        pyramid.append(image)

    return pyramid


def laplacian_pyramid(image: NDArray, levels: int = 3) -> list:
    """
    Create Laplacian pyramid.

    Args:
        image: Input image
        levels: Number of pyramid levels

    Returns:
        List of pyramid levels
    """
    # Build Gaussian pyramid
    gaussian_pyr = gaussian_pyramid(image, levels)

    # Build Laplacian pyramid
    laplacian_pyr = []

    for i in range(levels - 1):
        size = (gaussian_pyr[i].shape[1], gaussian_pyr[i].shape[0])
        expanded = cv2.pyrUp(gaussian_pyr[i + 1], dstsize=size)
        laplacian = cv2.subtract(gaussian_pyr[i], expanded)
        laplacian_pyr.append(laplacian)

    # Add the smallest level
    laplacian_pyr.append(gaussian_pyr[-1])

    return laplacian_pyr
