"""ResNet model with most of the code taken from
https://github.com/tensorflow/models/tree/master/resnet.

Related papers:
https://arxiv.org/pdf/1603.05027v2.pdf
https://arxiv.org/pdf/1512.03385v1.pdf
https://arxiv.org/pdf/1605.07146v1.pdf
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from collections import namedtuple
import numpy as np
import ray
import tensorflow as tf
from tensorflow.python.training import moving_averages

HParams = namedtuple('HParams',
                     'batch_size, num_classes, min_lrn_rate, lrn_rate, '
                     'num_residual_units, use_bottleneck, weight_decay_rate, '
                     'relu_leakiness, optimizer, num_gpus')


class ResNet(object):
    """ResNet model."""

    def __init__(self, hps, images, labels, mode):
        """ResNet constructor.

        Args:
            hps: Hyperparameters.
            images: Batches of images of size [batch_size, image_size,
                image_size, 3].
            labels: Batches of labels of size [batch_size, num_classes].
            mode: One of 'train' and 'eval'.
        """
        self.hps = hps
        self._images = images
        self.labels = labels
        self.mode = mode

        self._extra_train_ops = []

    def build_graph(self):
        """Build a whole graph for the model."""
        self.global_step = tf.Variable(0, trainable=False)
        self._build_model()
        if self.mode == 'train':
            self._build_train_op()
        else:
            # Additional initialization for the test network.
            self.variables = ray.experimental.TensorFlowVariables(self.cost)
            self.summaries = tf.summary.merge_all()

    def _stride_arr(self, stride):
        """Map a stride scalar to the stride array for tf.nn.conv2d."""
        return [1, stride, stride, 1]

    def _build_model(self):
        """Build the core model within the graph."""

        with tf.variable_scope('init'):
            x = self._conv('init_conv', self._images, 3, 3, 16,
                           self._stride_arr(1))

        strides = [1, 2, 2]
        activate_before_residual = [True, False, False]
        if self.hps.use_bottleneck:
            res_func = self._bottleneck_residual
            filters = [16, 64, 128, 256]
        else:
            res_func = self._residual
            filters = [16, 16, 32, 64]

        with tf.variable_scope('unit_1_0'):
            x = res_func(x, filters[0], filters[1],
                         self._stride_arr(strides[0]),
                         activate_before_residual[0])
        for i in range(1, self.hps.num_residual_units):
            with tf.variable_scope('unit_1_%d' % i):
                x = res_func(x, filters[1], filters[1], self._stride_arr(1),
                             False)

        with tf.variable_scope('unit_2_0'):
            x = res_func(x, filters[1], filters[2],
                         self._stride_arr(strides[1]),
                         activate_before_residual[1])
        for i in range(1, self.hps.num_residual_units):
            with tf.variable_scope('unit_2_%d' % i):
                x = res_func(x, filters[2], filters[2],
                             self._stride_arr(1), False)

        with tf.variable_scope('unit_3_0'):
            x = res_func(x, filters[2], filters[3],
                         self._stride_arr(strides[2]),
                         activate_before_residual[2])
        for i in range(1, self.hps.num_residual_units):
            with tf.variable_scope('unit_3_%d' % i):
                x = res_func(x, filters[3], filters[3], self._stride_arr(1),
                             False)
        with tf.variable_scope('unit_last'):
            x = self._batch_norm('final_bn', x)
            x = self._relu(x, self.hps.relu_leakiness)
            x = self._global_avg_pool(x)

        with tf.variable_scope('logit'):
            logits = self._fully_connected(x, self.hps.num_classes)
            self.predictions = tf.nn.softmax(logits)

        with tf.variable_scope('costs'):
            xent = tf.nn.softmax_cross_entropy_with_logits(
                logits=logits, labels=self.labels)
            self.cost = tf.reduce_mean(xent, name='xent')
            self.cost += self._decay()

            if self.mode == 'eval':
                tf.summary.scalar('cost', self.cost)

    def _build_train_op(self):
        """Build training specific ops for the graph."""
        num_gpus = self.hps.num_gpus if self.hps.num_gpus != 0 else 1
        # The learning rate schedule is dependent on the number of gpus.
        boundaries = [int(20000 * i / np.sqrt(num_gpus)) for i in range(2, 5)]
        values = [0.1, 0.01, 0.001, 0.0001]
        self.lrn_rate = tf.train.piecewise_constant(self.global_step,
                                                    boundaries, values)
        tf.summary.scalar('learning rate', self.lrn_rate)

        if self.hps.optimizer == 'sgd':
            optimizer = tf.train.GradientDescentOptimizer(self.lrn_rate)
        elif self.hps.optimizer == 'mom':
            optimizer = tf.train.MomentumOptimizer(self.lrn_rate, 0.9)

        apply_op = optimizer.minimize(self.cost, global_step=self.global_step)
        train_ops = [apply_op] + self._extra_train_ops
        self.train_op = tf.group(*train_ops)
        self.variables = ray.experimental.TensorFlowVariables(self.train_op)

    def _batch_norm(self, name, x):
        """Batch normalization."""
        with tf.variable_scope(name):
            params_shape = [x.get_shape()[-1]]

            beta = tf.get_variable(
                'beta', params_shape, tf.float32,
                initializer=tf.constant_initializer(0.0, tf.float32))
            gamma = tf.get_variable(
                'gamma', params_shape, tf.float32,
                initializer=tf.constant_initializer(1.0, tf.float32))

            if self.mode == 'train':
                mean, variance = tf.nn.moments(x, [0, 1, 2], name='moments')

                moving_mean = tf.get_variable(
                    'moving_mean', params_shape, tf.float32,
                    initializer=tf.constant_initializer(0.0, tf.float32),
                    trainable=False)
                moving_variance = tf.get_variable(
                    'moving_variance', params_shape, tf.float32,
                    initializer=tf.constant_initializer(1.0, tf.float32),
                    trainable=False)

                self._extra_train_ops.append(
                    moving_averages.assign_moving_average(moving_mean, mean,
                                                          0.9))
                self._extra_train_ops.append(
                    moving_averages.assign_moving_average(moving_variance,
                                                          variance, 0.9))
            else:
                mean = tf.get_variable(
                    'moving_mean', params_shape, tf.float32,
                    initializer=tf.constant_initializer(0.0, tf.float32),
                    trainable=False)
                variance = tf.get_variable(
                    'moving_variance', params_shape, tf.float32,
                    initializer=tf.constant_initializer(1.0, tf.float32),
                    trainable=False)
                tf.summary.histogram(mean.op.name, mean)
                tf.summary.histogram(variance.op.name, variance)
            # elipson used to be 1e-5. Maybe 0.001 solves NaN problem in deeper
            # net.
            y = tf.nn.batch_normalization(
                x, mean, variance, beta, gamma, 0.001)
            y.set_shape(x.get_shape())
            return y

    def _residual(self, x, in_filter, out_filter, stride,
                  activate_before_residual=False):
        """Residual unit with 2 sub layers."""
        if activate_before_residual:
            with tf.variable_scope('shared_activation'):
                x = self._batch_norm('init_bn', x)
                x = self._relu(x, self.hps.relu_leakiness)
                orig_x = x
        else:
            with tf.variable_scope('residual_only_activation'):
                orig_x = x
                x = self._batch_norm('init_bn', x)
                x = self._relu(x, self.hps.relu_leakiness)

        with tf.variable_scope('sub1'):
            x = self._conv('conv1', x, 3, in_filter, out_filter, stride)

        with tf.variable_scope('sub2'):
            x = self._batch_norm('bn2', x)
            x = self._relu(x, self.hps.relu_leakiness)
            x = self._conv('conv2', x, 3, out_filter, out_filter, [1, 1, 1, 1])

        with tf.variable_scope('sub_add'):
            if in_filter != out_filter:
                orig_x = tf.nn.avg_pool(orig_x, stride, stride, 'VALID')
                orig_x = tf.pad(
                    orig_x, [[0, 0], [0, 0], [0, 0],
                             [(out_filter - in_filter) // 2,
                             (out_filter - in_filter) // 2]])
            x += orig_x

        return x

    def _bottleneck_residual(self, x, in_filter, out_filter, stride,
                             activate_before_residual=False):
        """Bottleneck residual unit with 3 sub layers."""
        if activate_before_residual:
            with tf.variable_scope('common_bn_relu'):
                x = self._batch_norm('init_bn', x)
                x = self._relu(x, self.hps.relu_leakiness)
                orig_x = x
        else:
            with tf.variable_scope('residual_bn_relu'):
                orig_x = x
                x = self._batch_norm('init_bn', x)
                x = self._relu(x, self.hps.relu_leakiness)

        with tf.variable_scope('sub1'):
            x = self._conv('conv1', x, 1, in_filter, out_filter / 4, stride)

        with tf.variable_scope('sub2'):
            x = self._batch_norm('bn2', x)
            x = self._relu(x, self.hps.relu_leakiness)
            x = self._conv('conv2', x, 3, out_filter / 4, out_filter / 4,
                           [1, 1, 1, 1])

        with tf.variable_scope('sub3'):
            x = self._batch_norm('bn3', x)
            x = self._relu(x, self.hps.relu_leakiness)
            x = self._conv('conv3', x, 1, out_filter / 4, out_filter,
                           [1, 1, 1, 1])

        with tf.variable_scope('sub_add'):
            if in_filter != out_filter:
                orig_x = self._conv('project', orig_x, 1, in_filter,
                                    out_filter, stride)
            x += orig_x

        return x

    def _decay(self):
        """L2 weight decay loss."""
        costs = []
        for var in tf.trainable_variables():
            if var.op.name.find(r'DW') > 0:
                costs.append(tf.nn.l2_loss(var))

        return tf.multiply(self.hps.weight_decay_rate, tf.add_n(costs))

    def _conv(self, name, x, filter_size, in_filters, out_filters, strides):
        """Convolution."""
        with tf.variable_scope(name):
            n = filter_size * filter_size * out_filters
            kernel = tf.get_variable(
                'DW', [filter_size, filter_size, in_filters, out_filters],
                tf.float32, initializer=tf.random_normal_initializer(
                    stddev=np.sqrt(2.0 / n)))
            return tf.nn.conv2d(x, kernel, strides, padding='SAME')

    def _relu(self, x, leakiness=0.0):
        """Relu, with optional leaky support."""
        return tf.where(tf.less(x, 0.0), leakiness * x, x, name='leaky_relu')

    def _fully_connected(self, x, out_dim):
        """FullyConnected layer for final output."""
        x = tf.reshape(x, [self.hps.batch_size, -1])
        w = tf.get_variable(
            'DW', [x.get_shape()[1], out_dim],
            initializer=tf.uniform_unit_scaling_initializer(factor=1.0))
        b = tf.get_variable('biases', [out_dim],
                            initializer=tf.constant_initializer())
        return tf.nn.xw_plus_b(x, w, b)

    def _global_avg_pool(self, x):
        assert x.get_shape().ndims == 4
        return tf.reduce_mean(x, [1, 2])
