# 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 math
import paddle
from paddle import ParamAttr
import paddle.nn as nn
import paddle.nn.functional as F
from paddle.nn import Conv2D, BatchNorm, AdaptiveAvgPool2D, Linear
from paddle.regularizer import L2Decay
from paddle.nn.initializer import Uniform, KaimingNormal

__all__ = ["GhostNet_x0_5", "GhostNet_x1_0", "GhostNet_x1_3"]


class ConvBNLayer(nn.Layer):
    def __init__(self,
                 in_channels,
                 out_channels,
                 kernel_size,
                 stride=1,
                 groups=1,
                 act="relu",
                 name=None):
        super(ConvBNLayer, self).__init__()
        self._conv = Conv2D(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=(kernel_size - 1) // 2,
            groups=groups,
            weight_attr=ParamAttr(
                initializer=KaimingNormal(), name=name + "_weights"),
            bias_attr=False)
        bn_name = name + "_bn"

        self._batch_norm = BatchNorm(
            num_channels=out_channels,
            act=act,
            param_attr=ParamAttr(
                name=bn_name + "_scale", regularizer=L2Decay(0.0)),
            bias_attr=ParamAttr(
                name=bn_name + "_offset", regularizer=L2Decay(0.0)),
            moving_mean_name=bn_name + "_mean",
            moving_variance_name=bn_name + "_variance")

    def forward(self, inputs):
        y = self._conv(inputs)
        y = self._batch_norm(y)
        return y


class SEBlock(nn.Layer):
    def __init__(self, num_channels, reduction_ratio=4, name=None):
        super(SEBlock, self).__init__()
        self.pool2d_gap = AdaptiveAvgPool2D(1)
        self._num_channels = num_channels
        stdv = 1.0 / math.sqrt(num_channels * 1.0)
        med_ch = num_channels // reduction_ratio
        self.squeeze = Linear(
            num_channels,
            med_ch,
            weight_attr=ParamAttr(
                initializer=Uniform(-stdv, stdv), name=name + "_1_weights"),
            bias_attr=ParamAttr(name=name + "_1_offset"))
        stdv = 1.0 / math.sqrt(med_ch * 1.0)
        self.excitation = Linear(
            med_ch,
            num_channels,
            weight_attr=ParamAttr(
                initializer=Uniform(-stdv, stdv), name=name + "_2_weights"),
            bias_attr=ParamAttr(name=name + "_2_offset"))

    def forward(self, inputs):
        pool = self.pool2d_gap(inputs)
        pool = paddle.squeeze(pool, axis=[2, 3])
        squeeze = self.squeeze(pool)
        squeeze = F.relu(squeeze)
        excitation = self.excitation(squeeze)
        excitation = paddle.clip(x=excitation, min=0, max=1)
        excitation = paddle.unsqueeze(excitation, axis=[2, 3])
        out = paddle.multiply(inputs, excitation)
        return out


class GhostModule(nn.Layer):
    def __init__(self,
                 in_channels,
                 output_channels,
                 kernel_size=1,
                 ratio=2,
                 dw_size=3,
                 stride=1,
                 relu=True,
                 name=None):
        super(GhostModule, self).__init__()
        init_channels = int(math.ceil(output_channels / ratio))
        new_channels = int(init_channels * (ratio - 1))
        self.primary_conv = ConvBNLayer(
            in_channels=in_channels,
            out_channels=init_channels,
            kernel_size=kernel_size,
            stride=stride,
            groups=1,
            act="relu" if relu else None,
            name=name + "_primary_conv")
        self.cheap_operation = ConvBNLayer(
            in_channels=init_channels,
            out_channels=new_channels,
            kernel_size=dw_size,
            stride=1,
            groups=init_channels,
            act="relu" if relu else None,
            name=name + "_cheap_operation")

    def forward(self, inputs):
        x = self.primary_conv(inputs)
        y = self.cheap_operation(x)
        out = paddle.concat([x, y], axis=1)
        return out


class GhostBottleneck(nn.Layer):
    def __init__(self,
                 in_channels,
                 hidden_dim,
                 output_channels,
                 kernel_size,
                 stride,
                 use_se,
                 name=None):
        super(GhostBottleneck, self).__init__()
        self._stride = stride
        self._use_se = use_se
        self._num_channels = in_channels
        self._output_channels = output_channels
        self.ghost_module_1 = GhostModule(
            in_channels=in_channels,
            output_channels=hidden_dim,
            kernel_size=1,
            stride=1,
            relu=True,
            name=name + "_ghost_module_1")
        if stride == 2:
            self.depthwise_conv = ConvBNLayer(
                in_channels=hidden_dim,
                out_channels=hidden_dim,
                kernel_size=kernel_size,
                stride=stride,
                groups=hidden_dim,
                act=None,
                name=name +
                "_depthwise_depthwise"  # looks strange due to an old typo, will be fixed later.
            )
        if use_se:
            self.se_block = SEBlock(num_channels=hidden_dim, name=name + "_se")
        self.ghost_module_2 = GhostModule(
            in_channels=hidden_dim,
            output_channels=output_channels,
            kernel_size=1,
            relu=False,
            name=name + "_ghost_module_2")
        if stride != 1 or in_channels != output_channels:
            self.shortcut_depthwise = ConvBNLayer(
                in_channels=in_channels,
                out_channels=in_channels,
                kernel_size=kernel_size,
                stride=stride,
                groups=in_channels,
                act=None,
                name=name +
                "_shortcut_depthwise_depthwise"  # looks strange due to an old typo, will be fixed later.
            )
            self.shortcut_conv = ConvBNLayer(
                in_channels=in_channels,
                out_channels=output_channels,
                kernel_size=1,
                stride=1,
                groups=1,
                act=None,
                name=name + "_shortcut_conv")

    def forward(self, inputs):
        x = self.ghost_module_1(inputs)
        if self._stride == 2:
            x = self.depthwise_conv(x)
        if self._use_se:
            x = self.se_block(x)
        x = self.ghost_module_2(x)
        if self._stride == 1 and self._num_channels == self._output_channels:
            shortcut = inputs
        else:
            shortcut = self.shortcut_depthwise(inputs)
            shortcut = self.shortcut_conv(shortcut)
        return paddle.add(x=x, y=shortcut)


class GhostNet(nn.Layer):
    def __init__(self, scale, class_dim=1000):
        super(GhostNet, self).__init__()
        self.cfgs = [
            # k, t, c, SE, s
            [3, 16, 16, 0, 1],
            [3, 48, 24, 0, 2],
            [3, 72, 24, 0, 1],
            [5, 72, 40, 1, 2],
            [5, 120, 40, 1, 1],
            [3, 240, 80, 0, 2],
            [3, 200, 80, 0, 1],
            [3, 184, 80, 0, 1],
            [3, 184, 80, 0, 1],
            [3, 480, 112, 1, 1],
            [3, 672, 112, 1, 1],
            [5, 672, 160, 1, 2],
            [5, 960, 160, 0, 1],
            [5, 960, 160, 1, 1],
            [5, 960, 160, 0, 1],
            [5, 960, 160, 1, 1]
        ]
        self.scale = scale
        output_channels = int(self._make_divisible(16 * self.scale, 4))
        self.conv1 = ConvBNLayer(
            in_channels=3,
            out_channels=output_channels,
            kernel_size=3,
            stride=2,
            groups=1,
            act="relu",
            name="conv1")
        # build inverted residual blocks
        idx = 0
        self.ghost_bottleneck_list = []
        for k, exp_size, c, use_se, s in self.cfgs:
            in_channels = output_channels
            output_channels = int(self._make_divisible(c * self.scale, 4))
            hidden_dim = int(self._make_divisible(exp_size * self.scale, 4))
            ghost_bottleneck = self.add_sublayer(
                name="_ghostbottleneck_" + str(idx),
                sublayer=GhostBottleneck(
                    in_channels=in_channels,
                    hidden_dim=hidden_dim,
                    output_channels=output_channels,
                    kernel_size=k,
                    stride=s,
                    use_se=use_se,
                    name="_ghostbottleneck_" + str(idx)))
            self.ghost_bottleneck_list.append(ghost_bottleneck)
            idx += 1
        # build last several layers
        in_channels = output_channels
        output_channels = int(self._make_divisible(exp_size * self.scale, 4))
        self.conv_last = ConvBNLayer(
            in_channels=in_channels,
            out_channels=output_channels,
            kernel_size=1,
            stride=1,
            groups=1,
            act="relu",
            name="conv_last")
        self.pool2d_gap = AdaptiveAvgPool2D(1)
        in_channels = output_channels
        self._fc0_output_channels = 1280
        self.fc_0 = ConvBNLayer(
            in_channels=in_channels,
            out_channels=self._fc0_output_channels,
            kernel_size=1,
            stride=1,
            act="relu",
            name="fc_0")
        self.dropout = nn.Dropout(p=0.2)
        stdv = 1.0 / math.sqrt(self._fc0_output_channels * 1.0)
        self.fc_1 = Linear(
            self._fc0_output_channels,
            class_dim,
            weight_attr=ParamAttr(
                name="fc_1_weights", initializer=Uniform(-stdv, stdv)),
            bias_attr=ParamAttr(name="fc_1_offset"))

    def forward(self, inputs):
        x = self.conv1(inputs)
        for ghost_bottleneck in self.ghost_bottleneck_list:
            x = ghost_bottleneck(x)
        x = self.conv_last(x)
        x = self.pool2d_gap(x)
        x = self.fc_0(x)
        x = self.dropout(x)
        x = paddle.reshape(x, shape=[-1, self._fc0_output_channels])
        x = self.fc_1(x)
        return x

    def _make_divisible(self, v, divisor, min_value=None):
        """
        This function is taken from the original tf repo.
        It ensures that all layers have a channel number that is divisible by 8
        It can be seen here:
        https://github.com/tensorflow/models/blob/master/research/slim/nets/mobilenet/mobilenet.py
        """
        if min_value is None:
            min_value = divisor
        new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
        # Make sure that round down does not go down by more than 10%.
        if new_v < 0.9 * v:
            new_v += divisor
        return new_v


def GhostNet_x0_5(**args):
    model = GhostNet(scale=0.5)
    return model


def GhostNet_x1_0(**args):
    model = GhostNet(scale=1.0)
    return model


def GhostNet_x1_3(**args):
    model = GhostNet(scale=1.3)
    return model
