# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you 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.

# pylint:skip-file
import sys

from mxnet.symbol_doc import SymbolDoc

sys.path.insert(0, "../../python")
import mxnet as mx
import numpy as np
from collections import namedtuple
import time
import math

LSTMState = namedtuple("LSTMState", ["c", "h"])
LSTMParam = namedtuple("LSTMParam", ["i2h_weight", "i2h_bias",
                                     "h2h_weight", "h2h_bias"])
LSTMModel = namedtuple("LSTMModel", ["rnn_exec", "symbol",
                                     "init_states", "last_states",
                                     "seq_data", "seq_labels", "seq_outputs",
                                     "param_blocks"])


def lstm(num_hidden, indata, prev_state, param, seqidx, layeridx):
    """LSTM Cell symbol"""
    i2h = mx.sym.FullyConnected(data=indata,
                                weight=param.i2h_weight,
                                bias=param.i2h_bias,
                                num_hidden=num_hidden * 4,
                                name="t%d_l%d_i2h" % (seqidx, layeridx))
    h2h = mx.sym.FullyConnected(data=prev_state.h,
                                weight=param.h2h_weight,
                                bias=param.h2h_bias,
                                num_hidden=num_hidden * 4,
                                name="t%d_l%d_h2h" % (seqidx, layeridx))
    gates = i2h + h2h
    slice_gates = mx.sym.SliceChannel(gates, num_outputs=4,
                                      name="t%d_l%d_slice" % (seqidx, layeridx))
    in_gate = mx.sym.Activation(slice_gates[0], act_type="sigmoid")
    in_transform = mx.sym.Activation(slice_gates[1], act_type="tanh")
    forget_gate = mx.sym.Activation(slice_gates[2], act_type="sigmoid")
    out_gate = mx.sym.Activation(slice_gates[3], act_type="sigmoid")
    next_c = (forget_gate * prev_state.c) + (in_gate * in_transform)
    next_h = out_gate * mx.sym.Activation(next_c, act_type="tanh")
    return LSTMState(c=next_c, h=next_h)


def lstm_unroll(num_lstm_layer, seq_len,
                num_hidden, num_label):
    param_cells = []
    last_states = []
    for i in range(num_lstm_layer):
        param_cells.append(LSTMParam(i2h_weight=mx.sym.Variable("l%d_i2h_weight" % i),
                                     i2h_bias=mx.sym.Variable("l%d_i2h_bias" % i),
                                     h2h_weight=mx.sym.Variable("l%d_h2h_weight" % i),
                                     h2h_bias=mx.sym.Variable("l%d_h2h_bias" % i)))
        state = LSTMState(c=mx.sym.Variable("l%d_init_c" % i),
                          h=mx.sym.Variable("l%d_init_h" % i))
        last_states.append(state)
    assert (len(last_states) == num_lstm_layer)

    # embeding layer
    data = mx.sym.Variable('data')
    label = mx.sym.Variable('label')
    wordvec = mx.sym.SliceChannel(data=data, num_outputs=seq_len, squeeze_axis=1)

    hidden_all = []
    for seqidx in range(seq_len):
        hidden = wordvec[seqidx]
        for i in range(num_lstm_layer):
            next_state = lstm(num_hidden, indata=hidden,
                              prev_state=last_states[i],
                              param=param_cells[i],
                              seqidx=seqidx, layeridx=i)
            hidden = next_state.h
            last_states[i] = next_state
        hidden_all.append(hidden)

    hidden_concat = mx.sym.Concat(*hidden_all, dim=0)

    pred_fc = mx.sym.FullyConnected(data=hidden_concat, num_hidden=11)
    pred_ctc = mx.sym.Reshape(data=pred_fc, shape=(-4, seq_len, -1, 0))

    loss = mx.sym.contrib.ctc_loss(data=pred_ctc, label=label)
    ctc_loss = mx.sym.MakeLoss(loss)

    softmax_class = mx.symbol.SoftmaxActivation(data=pred_fc)
    softmax_loss = mx.sym.MakeLoss(softmax_class)
    softmax_loss = mx.sym.BlockGrad(softmax_loss)

    return mx.sym.Group([softmax_loss, ctc_loss])
