# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

from collections import namedtuple
import torch
from torch.nn import Conv2d, BatchNorm2d, PReLU, ReLU, Sigmoid, MaxPool2d, AdaptiveAvgPool2d, Sequential, Module

"""
ArcFace implementation from [TreB1eN](https://github.com/TreB1eN/InsightFace_Pytorch)
"""


class Flatten(Module):
	def forward(self, input):
		return input.view(input.size(0), -1)


def l2_norm(input, axis=1):
	norm = torch.norm(input, 2, axis, True)
	output = torch.div(input, norm)
	return output


class Bottleneck(namedtuple('Block', ['in_channel', 'depth', 'stride'])):
	""" A named tuple describing a ResNet block. """


def get_block(in_channel, depth, num_units, stride=2):
	return [Bottleneck(in_channel, depth, stride)] + [Bottleneck(depth, depth, 1) for i in range(num_units - 1)]


def get_blocks(num_layers):
	if num_layers == 50:
		blocks = [
			get_block(in_channel=64, depth=64, num_units=3),
			get_block(in_channel=64, depth=128, num_units=4),
			get_block(in_channel=128, depth=256, num_units=14),
			get_block(in_channel=256, depth=512, num_units=3)
		]
	elif num_layers == 100:
		blocks = [
			get_block(in_channel=64, depth=64, num_units=3),
			get_block(in_channel=64, depth=128, num_units=13),
			get_block(in_channel=128, depth=256, num_units=30),
			get_block(in_channel=256, depth=512, num_units=3)
		]
	elif num_layers == 152:
		blocks = [
			get_block(in_channel=64, depth=64, num_units=3),
			get_block(in_channel=64, depth=128, num_units=8),
			get_block(in_channel=128, depth=256, num_units=36),
			get_block(in_channel=256, depth=512, num_units=3)
		]
	else:
		raise ValueError("Invalid number of layers: {}. Must be one of [50, 100, 152]".format(num_layers))
	return blocks


class SEModule(Module):
	def __init__(self, channels, reduction):
		super(SEModule, self).__init__()
		self.avg_pool = AdaptiveAvgPool2d(1)
		self.fc1 = Conv2d(channels, channels // reduction, kernel_size=1, padding=0, bias=False)
		self.relu = ReLU(inplace=True)
		self.fc2 = Conv2d(channels // reduction, channels, kernel_size=1, padding=0, bias=False)
		self.sigmoid = Sigmoid()

	def forward(self, x):
		module_input = x
		x = self.avg_pool(x)
		x = self.fc1(x)
		x = self.relu(x)
		x = self.fc2(x)
		x = self.sigmoid(x)
		return module_input * x


class bottleneck_IR(Module):
	def __init__(self, in_channel, depth, stride):
		super(bottleneck_IR, self).__init__()
		if in_channel == depth:
			self.shortcut_layer = MaxPool2d(1, stride)
		else:
			self.shortcut_layer = Sequential(
				Conv2d(in_channel, depth, (1, 1), stride, bias=False),
				BatchNorm2d(depth)
			)
		self.res_layer = Sequential(
			BatchNorm2d(in_channel),
			Conv2d(in_channel, depth, (3, 3), (1, 1), 1, bias=False), PReLU(depth),
			Conv2d(depth, depth, (3, 3), stride, 1, bias=False), BatchNorm2d(depth)
		)

	def forward(self, x):
		shortcut = self.shortcut_layer(x)
		res = self.res_layer(x)
		return res + shortcut


class bottleneck_IR_SE(Module):
	def __init__(self, in_channel, depth, stride):
		super(bottleneck_IR_SE, self).__init__()
		if in_channel == depth:
			self.shortcut_layer = MaxPool2d(1, stride)
		else:
			self.shortcut_layer = Sequential(
				Conv2d(in_channel, depth, (1, 1), stride, bias=False),
				BatchNorm2d(depth)
			)
		self.res_layer = Sequential(
			BatchNorm2d(in_channel),
			Conv2d(in_channel, depth, (3, 3), (1, 1), 1, bias=False),
			PReLU(depth),
			Conv2d(depth, depth, (3, 3), stride, 1, bias=False),
			BatchNorm2d(depth),
			SEModule(depth, 16)
		)

	def forward(self, x):
		shortcut = self.shortcut_layer(x)
		res = self.res_layer(x)
		return res + shortcut
