# -*- coding: utf-8 -*-
"""Inception-ResNet V1 model for tensorflow.keras.
# Reference
http://arxiv.org/abs/1602.07261
https://github.com/davidsandberg/facenet/blob/master/src/models/inception_resnet_v1.py
https://github.com/myutwo150/keras-inception-resnet-v2/blob/master/inception_resnet_v2.py
"""
from functools import partial

from tensorflow.keras.models import Model
from tensorflow.keras.layers import Activation
from tensorflow.keras.layers import BatchNormalization
from tensorflow.keras.layers import Concatenate
from tensorflow.keras.layers import Conv2D
from tensorflow.keras.layers import Dense
from tensorflow.keras.layers import Dropout
from tensorflow.keras.layers import GlobalAveragePooling2D
from tensorflow.keras.layers import Input
from tensorflow.keras.layers import Lambda
from tensorflow.keras.layers import MaxPooling2D
from tensorflow.keras.layers import add
from tensorflow.keras import backend as K


def scaling(x, scale):
    return x * scale


def conv2d_bn(x,
              filters,
              kernel_size,
              strides=1,
              padding='same',
              activation='relu',
              use_bias=False,
              name=None):
    x = Conv2D(filters,
               kernel_size,
               strides=strides,
               padding=padding,
               use_bias=use_bias,
               name=name)(x)
    if not use_bias:
        bn_axis = 1 if K.image_data_format() == 'channels_first' else 3
        bn_name = _generate_layer_name('BatchNorm', prefix=name)
        x = BatchNormalization(axis=bn_axis,
                               momentum=0.995,
                               epsilon=0.001,
                               scale=False,
                               name=bn_name)(x)
    if activation is not None:
        ac_name = _generate_layer_name('Activation', prefix=name)
        x = Activation(activation, name=ac_name)(x)
    return x


def _generate_layer_name(name, branch_idx=None, prefix=None):
    if prefix is None:
        return None
    if branch_idx is None:
        return '_'.join((prefix, name))
    return '_'.join((prefix, 'Branch', str(branch_idx), name))


def _inception_resnet_block(x, scale, block_type, block_idx,
                            activation='relu'):
    channel_axis = 1 if K.image_data_format() == 'channels_first' else 3
    if block_idx is None:
        prefix = None
    else:
        prefix = '_'.join((block_type, str(block_idx)))
    name_fmt = partial(_generate_layer_name, prefix=prefix)

    if block_type == 'Block35':
        branch_0 = conv2d_bn(x, 32, 1, name=name_fmt('Conv2d_1x1', 0))
        branch_1 = conv2d_bn(x, 32, 1, name=name_fmt('Conv2d_0a_1x1', 1))
        branch_1 = conv2d_bn(branch_1,
                             32,
                             3,
                             name=name_fmt('Conv2d_0b_3x3', 1))
        branch_2 = conv2d_bn(x, 32, 1, name=name_fmt('Conv2d_0a_1x1', 2))
        branch_2 = conv2d_bn(branch_2,
                             32,
                             3,
                             name=name_fmt('Conv2d_0b_3x3', 2))
        branch_2 = conv2d_bn(branch_2,
                             32,
                             3,
                             name=name_fmt('Conv2d_0c_3x3', 2))
        branches = [branch_0, branch_1, branch_2]
    elif block_type == 'Block17':
        branch_0 = conv2d_bn(x, 128, 1, name=name_fmt('Conv2d_1x1', 0))
        branch_1 = conv2d_bn(x, 128, 1, name=name_fmt('Conv2d_0a_1x1', 1))
        branch_1 = conv2d_bn(branch_1,
                             128, [1, 7],
                             name=name_fmt('Conv2d_0b_1x7', 1))
        branch_1 = conv2d_bn(branch_1,
                             128, [7, 1],
                             name=name_fmt('Conv2d_0c_7x1', 1))
        branches = [branch_0, branch_1]
    elif block_type == 'Block8':
        branch_0 = conv2d_bn(x, 192, 1, name=name_fmt('Conv2d_1x1', 0))
        branch_1 = conv2d_bn(x, 192, 1, name=name_fmt('Conv2d_0a_1x1', 1))
        branch_1 = conv2d_bn(branch_1,
                             192, [1, 3],
                             name=name_fmt('Conv2d_0b_1x3', 1))
        branch_1 = conv2d_bn(branch_1,
                             192, [3, 1],
                             name=name_fmt('Conv2d_0c_3x1', 1))
        branches = [branch_0, branch_1]
    else:
        raise ValueError('Unknown Inception-ResNet block type. '
                         'Expects "Block35", "Block17" or "Block8", '
                         'but got: ' + str(block_type))

    mixed = Concatenate(axis=channel_axis,
                        name=name_fmt('Concatenate'))(branches)
    up = conv2d_bn(mixed,
                   K.int_shape(x)[channel_axis],
                   1,
                   activation=None,
                   use_bias=True,
                   name=name_fmt('Conv2d_1x1'))
    up = Lambda(scaling,
                output_shape=K.int_shape(up)[1:],
                arguments={'scale': scale})(up)
    x = add([x, up])
    if activation is not None:
        x = Activation(activation, name=name_fmt('Activation'))(x)
    return x


def InceptionResNetV1(input_shape=(160, 160, 3),
                      classes=128,
                      dropout_keep_prob=0.8,
                      weights_path=None):
    inputs = Input(shape=input_shape)
    x = conv2d_bn(inputs,
                  32,
                  3,
                  strides=2,
                  padding='valid',
                  name='Conv2d_1a_3x3')
    x = conv2d_bn(x, 32, 3, padding='valid', name='Conv2d_2a_3x3')
    x = conv2d_bn(x, 64, 3, name='Conv2d_2b_3x3')
    x = MaxPooling2D(3, strides=2, name='MaxPool_3a_3x3')(x)
    x = conv2d_bn(x, 80, 1, padding='valid', name='Conv2d_3b_1x1')
    x = conv2d_bn(x, 192, 3, padding='valid', name='Conv2d_4a_3x3')
    x = conv2d_bn(x, 256, 3, strides=2, padding='valid', name='Conv2d_4b_3x3')

    # 5x Block35 (Inception-ResNet-A block):
    for block_idx in range(1, 6):
        x = _inception_resnet_block(x,
                                    scale=0.17,
                                    block_type='Block35',
                                    block_idx=block_idx)

    # Mixed 6a (Reduction-A block):
    channel_axis = 1 if K.image_data_format() == 'channels_first' else 3
    name_fmt = partial(_generate_layer_name, prefix='Mixed_6a')
    branch_0 = conv2d_bn(x,
                         384,
                         3,
                         strides=2,
                         padding='valid',
                         name=name_fmt('Conv2d_1a_3x3', 0))
    branch_1 = conv2d_bn(x, 192, 1, name=name_fmt('Conv2d_0a_1x1', 1))
    branch_1 = conv2d_bn(branch_1, 192, 3, name=name_fmt('Conv2d_0b_3x3', 1))
    branch_1 = conv2d_bn(branch_1,
                         256,
                         3,
                         strides=2,
                         padding='valid',
                         name=name_fmt('Conv2d_1a_3x3', 1))
    branch_pool = MaxPooling2D(3,
                               strides=2,
                               padding='valid',
                               name=name_fmt('MaxPool_1a_3x3', 2))(x)
    branches = [branch_0, branch_1, branch_pool]
    x = Concatenate(axis=channel_axis, name='Mixed_6a')(branches)

    # 10x Block17 (Inception-ResNet-B block):
    for block_idx in range(1, 11):
        x = _inception_resnet_block(x,
                                    scale=0.1,
                                    block_type='Block17',
                                    block_idx=block_idx)

    # Mixed 7a (Reduction-B block): 8 x 8 x 2080
    name_fmt = partial(_generate_layer_name, prefix='Mixed_7a')
    branch_0 = conv2d_bn(x, 256, 1, name=name_fmt('Conv2d_0a_1x1', 0))
    branch_0 = conv2d_bn(branch_0,
                         384,
                         3,
                         strides=2,
                         padding='valid',
                         name=name_fmt('Conv2d_1a_3x3', 0))
    branch_1 = conv2d_bn(x, 256, 1, name=name_fmt('Conv2d_0a_1x1', 1))
    branch_1 = conv2d_bn(branch_1,
                         256,
                         3,
                         strides=2,
                         padding='valid',
                         name=name_fmt('Conv2d_1a_3x3', 1))
    branch_2 = conv2d_bn(x, 256, 1, name=name_fmt('Conv2d_0a_1x1', 2))
    branch_2 = conv2d_bn(branch_2, 256, 3, name=name_fmt('Conv2d_0b_3x3', 2))
    branch_2 = conv2d_bn(branch_2,
                         256,
                         3,
                         strides=2,
                         padding='valid',
                         name=name_fmt('Conv2d_1a_3x3', 2))
    branch_pool = MaxPooling2D(3,
                               strides=2,
                               padding='valid',
                               name=name_fmt('MaxPool_1a_3x3', 3))(x)
    branches = [branch_0, branch_1, branch_2, branch_pool]
    x = Concatenate(axis=channel_axis, name='Mixed_7a')(branches)

    # 5x Block8 (Inception-ResNet-C block):
    for block_idx in range(1, 6):
        x = _inception_resnet_block(x,
                                    scale=0.2,
                                    block_type='Block8',
                                    block_idx=block_idx)
    x = _inception_resnet_block(x,
                                scale=1.,
                                activation=None,
                                block_type='Block8',
                                block_idx=6)

    # Classification block
    x = GlobalAveragePooling2D(name='AvgPool')(x)
    x = Dropout(1.0 - dropout_keep_prob, name='Dropout')(x)
    # Bottleneck
    x = Dense(classes, use_bias=False, name='Bottleneck')(x)
    bn_name = _generate_layer_name('BatchNorm', prefix='Bottleneck')
    x = BatchNormalization(momentum=0.995,
                           epsilon=0.001,
                           scale=False,
                           name=bn_name)(x)
    x = Lambda(K.l2_normalize, arguments={'axis': 1}, name='normalize')(x)

    # Create model
    model = Model(inputs, x, name='inception_resnet_v1')
    if weights_path is not None:
        model.load_weights(weights_path)

    return model
