# Copyright 2019 Akiomi Kamakura
#
# 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 numpy as np
from PIL import Image, ImageChops

from pilgram.css.blending.alpha import alpha_blend


def _exclusion(im1, im2):
    """The exclusion blend mode.

    Arguments:
        im1: A backdrop image (RGB).
        im2: A source image (RGB).

    Returns:
        The output image.
    """

    screen = np.asarray(ImageChops.screen(im1, im2))
    multiply = np.asarray(ImageChops.multiply(im1, im2))

    return Image.fromarray(screen - multiply)


def exclusion(im1, im2):
    """Produces an effect like Difference but lower in contrast.

    The exclusion formula is defined as:

        B(Cb, Cs) = Cb + Cs - 2 x Cb x Cs

    See the W3C document:
    https://www.w3.org/TR/compositing-1/#blendingexclusion

    Arguments:
        im1: A backdrop image (RGB or RGBA).
        im2: A source image (RGB or RGBA).

    Returns:
        The output image.
    """

    return alpha_blend(im1, im2, _exclusion)
