import math
import torch 
import cv2 
import torch.nn as nn 
import torch.nn.functional as F
import numpy as np
    
class HOGGenerator(nn.Module):
    """Generate HOG feature for images.

    This module is used in MaskFeat to generate HOG feature. The code is
    modified from file `slowfast/models/operators.py
    <https://github.com/facebookresearch/SlowFast/blob/main/slowfast/models/operators.py>`_.
    Here is the link of `HOG wikipedia
    <https://en.wikipedia.org/wiki/Histogram_of_oriented_gradients>`_.

    Args:
        nbins (int): Number of bin. Defaults to 9.
        pool (float): Number of cell. Defaults to 8.
        gaussian_window (int): Size of gaussian kernel. Defaults to 16.
    """

    def __init__(self,
                 nbins: int = 9,
                 pool: int = 8,
                 gaussian_window: int = 16) -> None:
        super().__init__()
        self.nbins = nbins
        self.pool = pool
        self.pi = math.pi
        weight_x = torch.FloatTensor([[1, 0, -1], [2, 0, -2], [1, 0, -1]])
        weight_x = weight_x.view(1, 1, 3, 3).repeat(3, 1, 1, 1).contiguous()
        weight_y = weight_x.transpose(2, 3).contiguous()
        self.register_buffer('weight_x', weight_x)
        self.register_buffer('weight_y', weight_y)

        self.gaussian_window = gaussian_window
        if gaussian_window:
            gaussian_kernel = self.get_gaussian_kernel(gaussian_window,
                                                       gaussian_window // 2)
            self.register_buffer('gaussian_kernel', gaussian_kernel)

    def get_gaussian_kernel(self, kernlen: int, std: int) -> torch.Tensor:
        """Returns a 2D Gaussian kernel array."""

        def _gaussian_fn(kernlen: int, std: int) -> torch.Tensor:
            n = torch.arange(0, kernlen).float()
            n -= n.mean()
            n /= std
            w = torch.exp(-0.5 * n**2)
            return w

        kernel_1d = _gaussian_fn(kernlen, std)
        kernel_2d = kernel_1d[:, None] * kernel_1d[None, :]
        return kernel_2d / kernel_2d.sum()

    def _reshape(self, hog_feat: torch.Tensor) -> torch.Tensor:
        """Reshape HOG Features for output."""
        hog_feat = hog_feat.flatten(1, 2)
        self.unfold_size = hog_feat.shape[-1] // 16
        hog_feat = hog_feat.permute(0, 2, 3, 1)
        # print(hog_feat.shape)
        hog_feat = hog_feat.unfold(1, self.unfold_size,
                                   self.unfold_size).unfold(
                                       2, self.unfold_size, self.unfold_size)
        hog_feat = hog_feat.flatten(1, 2).flatten(2)
        return hog_feat

    @torch.no_grad()
    def forward(self, x: torch.Tensor) -> torch.Tensor:
        """Generate hog feature for each batch images.

        Args:
            x (torch.Tensor): Input images of shape (N, 3, H, W).

        Returns:
            torch.Tensor: Hog features.
        """
        # input is RGB image with shape [B 3 H W]
        self.h, self.w = x.size(-2), x.size(-1)
        x = F.pad(x, pad=(1, 1, 1, 1), mode='reflect')
        gx_rgb = F.conv2d(
            x, self.weight_x, bias=None, stride=1, padding=0, groups=3)
        gy_rgb = F.conv2d(
            x, self.weight_y, bias=None, stride=1, padding=0, groups=3)
        norm_rgb = torch.stack([gx_rgb, gy_rgb], dim=-1).norm(dim=-1)
        phase = torch.atan2(gx_rgb, gy_rgb)
        phase = phase / self.pi * self.nbins  # [-9, 9]

        b, c, h, w = norm_rgb.shape
        out = torch.zeros((b, c, self.nbins, h, w),
                          dtype=torch.float,
                          device=x.device)
        phase = phase.view(b, c, 1, h, w)
        norm_rgb = norm_rgb.view(b, c, 1, h, w)
        if self.gaussian_window:
            if h != self.gaussian_window:
                assert h % self.gaussian_window == 0, 'h {} gw {}'.format(
                    h, self.gaussian_window)
                repeat_rate = h // self.gaussian_window
                temp_gaussian_kernel = self.gaussian_kernel.repeat(
                    [repeat_rate, repeat_rate])
            else:
                temp_gaussian_kernel = self.gaussian_kernel
            norm_rgb *= temp_gaussian_kernel

        out.scatter_add_(2, phase.floor().long() % self.nbins, norm_rgb)

        out = out.unfold(3, self.pool, self.pool)
        out = out.unfold(4, self.pool, self.pool)
        out = out.sum(dim=[-1, -2])

        self.out = F.normalize(out, p=2, dim=2)

        return self._reshape(self.out)

    def generate_hog_image(self, hog_out: torch.Tensor) -> np.ndarray:
        """Generate HOG image according to HOG features."""
        assert hog_out.size(0) == 1 and hog_out.size(1) == 3, \
            'Check the input batch size and the channcel number, only support'\
            '"batch_size = 1".'
        hog_image = np.zeros([self.h, self.w])
        cell_gradient = np.array(hog_out.mean(dim=1).squeeze().detach().cpu())
        cell_width = self.pool / 2
        max_mag = np.array(cell_gradient).max()
        angle_gap = 360 / self.nbins

        for x in range(cell_gradient.shape[1]):
            for y in range(cell_gradient.shape[2]):
                cell_grad = cell_gradient[:, x, y]
                cell_grad /= max_mag
                angle = 0
                for magnitude in cell_grad:
                    angle_radian = math.radians(angle)
                    x1 = int(x * self.pool +
                             magnitude * cell_width * math.cos(angle_radian))
                    y1 = int(y * self.pool +
                             magnitude * cell_width * math.sin(angle_radian))
                    x2 = int(x * self.pool -
                             magnitude * cell_width * math.cos(angle_radian))
                    y2 = int(y * self.pool -
                             magnitude * cell_width * math.sin(angle_radian))
                    magnitude = 0 if magnitude < 0 else magnitude
                    cv2.line(hog_image, (y1, x1), (y2, x2),
                             int(255 * math.sqrt(magnitude)))
                    angle += angle_gap
        return hog_image
