#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserve.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import cv2
import numpy as np
import paddle

from .builder import METRICS


@METRICS.register()
class PSNR(paddle.metric.Metric):
    def __init__(self, crop_border, input_order='HWC', test_y_channel=False):
        self.crop_border = crop_border
        self.input_order = input_order
        self.test_y_channel = test_y_channel
        self.reset()

    def reset(self):
        self.results = []

    def update(self, preds, gts):
        if not isinstance(preds, (list, tuple)):
            preds = [preds]

        if not isinstance(gts, (list, tuple)):
            gts = [gts]

        for pred, gt in zip(preds, gts):
            value = calculate_psnr(pred, gt, self.crop_border, self.input_order,
                                   self.test_y_channel)
            self.results.append(value)

    def accumulate(self):
        if len(self.results) <= 0:
            return 0.
        return np.mean(self.results)

    def name(self):
        return 'PSNR'


@METRICS.register()
class SSIM(PSNR):
    def update(self, preds, gts):
        if not isinstance(preds, (list, tuple)):
            preds = [preds]

        if not isinstance(gts, (list, tuple)):
            gts = [gts]

        for pred, gt in zip(preds, gts):
            value = calculate_ssim(pred, gt, self.crop_border, self.input_order,
                                   self.test_y_channel)
            self.results.append(value)

    def name(self):
        return 'SSIM'


def calculate_psnr(img1,
                   img2,
                   crop_border,
                   input_order='HWC',
                   test_y_channel=False):
    """Calculate PSNR (Peak Signal-to-Noise Ratio).

    Ref: https://en.wikipedia.org/wiki/Peak_signal-to-noise_ratio

    Args:
        img1 (ndarray): Images with range [0, 255].
        img2 (ndarray): Images with range [0, 255].
        crop_border (int): Cropped pixels in each edge of an image. These
            pixels are not involved in the PSNR calculation.
        input_order (str): Whether the input order is 'HWC' or 'CHW'.
            Default: 'HWC'.
        test_y_channel (bool): Test on Y channel of YCbCr. Default: False.

    Returns:
        float: psnr result.
    """

    assert img1.shape == img2.shape, (
        f'Image shapes are differnet: {img1.shape}, {img2.shape}.')
    if input_order not in ['HWC', 'CHW']:
        raise ValueError(
            f'Wrong input_order {input_order}. Supported input_orders are '
            '"HWC" and "CHW"')
    img1 = img1.copy().astype('float32')
    img2 = img2.copy().astype('float32')
    img1 = reorder_image(img1, input_order=input_order)
    img2 = reorder_image(img2, input_order=input_order)

    if crop_border != 0:
        img1 = img1[crop_border:-crop_border, crop_border:-crop_border, ...]
        img2 = img2[crop_border:-crop_border, crop_border:-crop_border, ...]

    if test_y_channel:
        img1 = to_y_channel(img1)
        img2 = to_y_channel(img2)

    mse = np.mean((img1 - img2)**2)
    if mse == 0:
        return float('inf')
    return 20. * np.log10(255. / np.sqrt(mse))


def _ssim(img1, img2):
    """Calculate SSIM (structural similarity) for one channel images.

    It is called by func:`calculate_ssim`.

    Args:
        img1 (ndarray): Images with range [0, 255] with order 'HWC'.
        img2 (ndarray): Images with range [0, 255] with order 'HWC'.

    Returns:
        float: ssim result.
    """

    C1 = (0.01 * 255)**2
    C2 = (0.03 * 255)**2

    img1 = img1.astype(np.float64)
    img2 = img2.astype(np.float64)
    kernel = cv2.getGaussianKernel(11, 1.5)
    window = np.outer(kernel, kernel.transpose())

    mu1 = cv2.filter2D(img1, -1, window)[5:-5, 5:-5]
    mu2 = cv2.filter2D(img2, -1, window)[5:-5, 5:-5]
    mu1_sq = mu1**2
    mu2_sq = mu2**2
    mu1_mu2 = mu1 * mu2
    sigma1_sq = cv2.filter2D(img1**2, -1, window)[5:-5, 5:-5] - mu1_sq
    sigma2_sq = cv2.filter2D(img2**2, -1, window)[5:-5, 5:-5] - mu2_sq
    sigma12 = cv2.filter2D(img1 * img2, -1, window)[5:-5, 5:-5] - mu1_mu2

    ssim_map = ((2 * mu1_mu2 + C1) *
                (2 * sigma12 + C2)) / ((mu1_sq + mu2_sq + C1) *
                                       (sigma1_sq + sigma2_sq + C2))
    return ssim_map.mean()


def calculate_ssim(img1,
                   img2,
                   crop_border,
                   input_order='HWC',
                   test_y_channel=False):
    """Calculate SSIM (structural similarity).

    Ref:
    Image quality assessment: From error visibility to structural similarity

    The results are the same as that of the official released MATLAB code in
    https://ece.uwaterloo.ca/~z70wang/research/ssim/.

    For three-channel images, SSIM is calculated for each channel and then
    averaged.

    Args:
        img1 (ndarray): Images with range [0, 255].
        img2 (ndarray): Images with range [0, 255].
        crop_border (int): Cropped pixels in each edge of an image. These
            pixels are not involved in the SSIM calculation.
        input_order (str): Whether the input order is 'HWC' or 'CHW'.
            Default: 'HWC'.
        test_y_channel (bool): Test on Y channel of YCbCr. Default: False.

    Returns:
        float: ssim result.
    """

    assert img1.shape == img2.shape, (
        f'Image shapes are differnet: {img1.shape}, {img2.shape}.')
    if input_order not in ['HWC', 'CHW']:
        raise ValueError(
            f'Wrong input_order {input_order}. Supported input_orders are '
            '"HWC" and "CHW"')

    img1 = img1.copy().astype('float32')[..., ::-1]
    img2 = img2.copy().astype('float32')[..., ::-1]

    img1 = reorder_image(img1, input_order=input_order)
    img2 = reorder_image(img2, input_order=input_order)

    if crop_border != 0:
        img1 = img1[crop_border:-crop_border, crop_border:-crop_border, ...]
        img2 = img2[crop_border:-crop_border, crop_border:-crop_border, ...]

    if test_y_channel:
        img1 = to_y_channel(img1)
        img2 = to_y_channel(img2)

    ssims = []
    for i in range(img1.shape[2]):
        ssims.append(_ssim(img1[..., i], img2[..., i]))
    return np.array(ssims).mean()


def reorder_image(img, input_order='HWC'):
    """Reorder images to 'HWC' order.

    If the input_order is (h, w), return (h, w, 1);
    If the input_order is (c, h, w), return (h, w, c);
    If the input_order is (h, w, c), return as it is.

    Args:
        img (ndarray): Input image.
        input_order (str): Whether the input order is 'HWC' or 'CHW'.
            If the input image shape is (h, w), input_order will not have
            effects. Default: 'HWC'.

    Returns:
        ndarray: reordered image.
    """

    if input_order not in ['HWC', 'CHW']:
        raise ValueError(
            f'Wrong input_order {input_order}. Supported input_orders are '
            "'HWC' and 'CHW'")
    if len(img.shape) == 2:
        img = img[..., None]
        return img
    if input_order == 'CHW':
        img = img.transpose(1, 2, 0)
    return img


def bgr2ycbcr(img, y_only=False):
    """Convert a BGR image to YCbCr image.

    The bgr version of rgb2ycbcr.
    It implements the ITU-R BT.601 conversion for standard-definition
    television. See more details in
    https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.

    It differs from a similar function in cv2.cvtColor: `BGR <-> YCrCb`.
    In OpenCV, it implements a JPEG conversion. See more details in
    https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion.

    Args:
        img (ndarray): The input image. It accepts:
            1. np.uint8 type with range [0, 255];
            2. np.float32 type with range [0, 1].
        y_only (bool): Whether to only return Y channel. Default: False.

    Returns:
        ndarray: The converted YCbCr image. The output image has the same type
            and range as input image.
    """
    img_type = img.dtype

    if y_only:
        out_img = np.dot(img, [24.966, 128.553, 65.481]) + 16.0
    else:
        out_img = np.matmul(
            img, [[24.966, 112.0, -18.214], [128.553, -74.203, -93.786],
                  [65.481, -37.797, 112.0]]) + [16, 128, 128]
    return out_img


def to_y_channel(img):
    """Change to Y channel of YCbCr.

    Args:
        img (ndarray): Images with range [0, 255].

    Returns:
        (ndarray): Images with range [0, 255] (float type) without round.
    """
    img = img.astype(np.float32) / 255.
    if img.ndim == 3 and img.shape[2] == 3:
        img = bgr2ycbcr(img, y_only=True)
        img = img[..., None]
    return img * 255.