import warnings
from torch.autograd import NestedIOFunction, Variable
import torch.backends.cudnn as cudnn
from .. import functional as F
from .thnn import rnnFusedPointwise as fusedBackend
import itertools

try:
    import torch.backends.cudnn.rnn
except ImportError:
    pass


def RNNReLUCell(input, hidden, w_ih, w_hh, b_ih=None, b_hh=None):
    hy = F.relu(F.linear(input, w_ih, b_ih) + F.linear(hidden, w_hh, b_hh))
    return hy


def RNNTanhCell(input, hidden, w_ih, w_hh, b_ih=None, b_hh=None):
    hy = F.tanh(F.linear(input, w_ih, b_ih) + F.linear(hidden, w_hh, b_hh))
    return hy


def LSTMCell(input, hidden, w_ih, w_hh, b_ih=None, b_hh=None):
    if input.is_cuda:
        igates = F.linear(input, w_ih)
        hgates = F.linear(hidden[0], w_hh)
        state = fusedBackend.LSTMFused.apply
        return state(igates, hgates, hidden[1]) if b_ih is None else state(igates, hgates, hidden[1], b_ih, b_hh)

    hx, cx = hidden
    gates = F.linear(input, w_ih, b_ih) + F.linear(hx, w_hh, b_hh)

    ingate, forgetgate, cellgate, outgate = gates.chunk(4, 1)

    ingate = F.sigmoid(ingate)
    forgetgate = F.sigmoid(forgetgate)
    cellgate = F.tanh(cellgate)
    outgate = F.sigmoid(outgate)

    cy = (forgetgate * cx) + (ingate * cellgate)
    hy = outgate * F.tanh(cy)

    return hy, cy


def GRUCell(input, hidden, w_ih, w_hh, b_ih=None, b_hh=None):

    if input.is_cuda:
        gi = F.linear(input, w_ih)
        gh = F.linear(hidden, w_hh)
        state = fusedBackend.GRUFused.apply
        return state(gi, gh, hidden) if b_ih is None else state(gi, gh, hidden, b_ih, b_hh)

    gi = F.linear(input, w_ih, b_ih)
    gh = F.linear(hidden, w_hh, b_hh)
    i_r, i_i, i_n = gi.chunk(3, 1)
    h_r, h_i, h_n = gh.chunk(3, 1)

    resetgate = F.sigmoid(i_r + h_r)
    inputgate = F.sigmoid(i_i + h_i)
    newgate = F.tanh(i_n + resetgate * h_n)
    hy = newgate + inputgate * (hidden - newgate)

    return hy


def StackedRNN(inners, num_layers, lstm=False, dropout=0, train=True):

    num_directions = len(inners)
    total_layers = num_layers * num_directions

    def forward(input, hidden, weight, batch_sizes):
        assert(len(weight) == total_layers)
        next_hidden = []

        if lstm:
            hidden = list(zip(*hidden))

        for i in range(num_layers):
            all_output = []
            for j, inner in enumerate(inners):
                l = i * num_directions + j

                hy, output = inner(input, hidden[l], weight[l], batch_sizes)
                next_hidden.append(hy)
                all_output.append(output)

            input = torch.cat(all_output, input.dim() - 1)

            if dropout != 0 and i < num_layers - 1:
                input = F.dropout(input, p=dropout, training=train, inplace=False)

        if lstm:
            next_h, next_c = zip(*next_hidden)
            next_hidden = (
                torch.cat(next_h, 0).view(total_layers, *next_h[0].size()),
                torch.cat(next_c, 0).view(total_layers, *next_c[0].size())
            )
        else:
            next_hidden = torch.cat(next_hidden, 0).view(
                total_layers, *next_hidden[0].size())

        return next_hidden, input

    return forward


def Recurrent(inner, reverse=False):
    def forward(input, hidden, weight, batch_sizes):
        output = []
        steps = range(input.size(0) - 1, -1, -1) if reverse else range(input.size(0))
        for i in steps:
            hidden = inner(input[i], hidden, *weight)
            # hack to handle LSTM
            output.append(hidden[0] if isinstance(hidden, tuple) else hidden)

        if reverse:
            output.reverse()
        output = torch.cat(output, 0).view(input.size(0), *output[0].size())

        return hidden, output

    return forward


def variable_recurrent_factory(inner, reverse=False):
    if reverse:
        return VariableRecurrentReverse(inner)
    else:
        return VariableRecurrent(inner)


def VariableRecurrent(inner):
    def forward(input, hidden, weight, batch_sizes):

        output = []
        input_offset = 0
        last_batch_size = batch_sizes[0]
        hiddens = []
        flat_hidden = not isinstance(hidden, tuple)
        if flat_hidden:
            hidden = (hidden,)
        for batch_size in batch_sizes:
            step_input = input[input_offset:input_offset + batch_size]
            input_offset += batch_size

            dec = last_batch_size - batch_size
            if dec > 0:
                hiddens.append(tuple(h[-dec:] for h in hidden))
                hidden = tuple(h[:-dec] for h in hidden)
            last_batch_size = batch_size

            if flat_hidden:
                hidden = (inner(step_input, hidden[0], *weight),)
            else:
                hidden = inner(step_input, hidden, *weight)

            output.append(hidden[0])
        hiddens.append(hidden)
        hiddens.reverse()

        hidden = tuple(torch.cat(h, 0) for h in zip(*hiddens))
        assert hidden[0].size(0) == batch_sizes[0]
        if flat_hidden:
            hidden = hidden[0]
        output = torch.cat(output, 0)

        return hidden, output

    return forward


def VariableRecurrentReverse(inner):
    def forward(input, hidden, weight, batch_sizes):
        output = []
        input_offset = input.size(0)
        last_batch_size = batch_sizes[-1]
        initial_hidden = hidden
        flat_hidden = not isinstance(hidden, tuple)
        if flat_hidden:
            hidden = (hidden,)
            initial_hidden = (initial_hidden,)
        hidden = tuple(h[:batch_sizes[-1]] for h in hidden)
        for i in reversed(range(len(batch_sizes))):
            batch_size = batch_sizes[i]
            inc = batch_size - last_batch_size
            if inc > 0:
                hidden = tuple(torch.cat((h, ih[last_batch_size:batch_size]), 0)
                               for h, ih in zip(hidden, initial_hidden))
            last_batch_size = batch_size
            step_input = input[input_offset - batch_size:input_offset]
            input_offset -= batch_size

            if flat_hidden:
                hidden = (inner(step_input, hidden[0], *weight),)
            else:
                hidden = inner(step_input, hidden, *weight)
            output.append(hidden[0])

        output.reverse()
        output = torch.cat(output, 0)
        if flat_hidden:
            hidden = hidden[0]
        return hidden, output

    return forward


def AutogradRNN(mode, input_size, hidden_size, num_layers=1, batch_first=False,
                dropout=0, train=True, bidirectional=False, variable_length=False,
                dropout_state=None, flat_weight=None):

    if mode == 'RNN_RELU':
        cell = RNNReLUCell
    elif mode == 'RNN_TANH':
        cell = RNNTanhCell
    elif mode == 'LSTM':
        cell = LSTMCell
    elif mode == 'GRU':
        cell = GRUCell
    else:
        raise Exception('Unknown mode: {}'.format(mode))

    rec_factory = variable_recurrent_factory if variable_length else Recurrent

    if bidirectional:
        layer = (rec_factory(cell), rec_factory(cell, reverse=True))
    else:
        layer = (rec_factory(cell),)

    func = StackedRNN(layer,
                      num_layers,
                      (mode == 'LSTM'),
                      dropout=dropout,
                      train=train)

    def forward(input, weight, hidden, batch_sizes):
        if batch_first and not variable_length:
            input = input.transpose(0, 1)

        nexth, output = func(input, hidden, weight, batch_sizes)

        if batch_first and not variable_length:
            output = output.transpose(0, 1)

        return output, nexth

    return forward


def CudnnRNN(mode, input_size, hidden_size, num_layers=1,
             batch_first=False, dropout=0, train=True, bidirectional=False,
             variable_length=False, dropout_state=None, flat_weight=None):
    if dropout_state is None:
        dropout_state = {}
    mode = cudnn.rnn.get_cudnn_mode(mode)
    dropout_seed = torch.IntTensor(1).random_()[0]
    if flat_weight is None:
        warnings.warn("RNN module weights are not part of single contiguous "
                      "chunk of memory. This means they need to be compacted "
                      "at every call, possibly greatly increasing memory usage. "
                      "To compact weights again call flatten_parameters().", stacklevel=5)

    def forward(input, weight, hx, batch_sizes):
        if mode == cudnn.CUDNN_LSTM:
            hx, cx = hx
        else:
            cx = None

        handle = cudnn.get_handle()
        dropout_desc = cudnn.rnn.init_dropout_descriptor(handle, dropout, train, dropout_seed, dropout_state)

        weight_arr = list(itertools.chain.from_iterable(weight))
        weight_stride0 = len(weight[0])

        output, hy, cy, reserve, new_weight_buf = torch._C._VariableFunctions._cudnn_rnn(
            input, weight_arr, weight_stride0,
            Variable(flat_weight) if flat_weight is not None else None,
            hx, cx,
            mode, hidden_size, num_layers,
            batch_first, dropout, train, bool(bidirectional),
            list(batch_sizes.data) if variable_length else (),
            Variable(dropout_desc.state) if dropout_desc.state is not None else None)

        if cx is not None:
            return (output, (hy, cy))
        else:
            return (output, hy)

    return forward


def RNN(*args, **kwargs):

    def forward(input, *fargs, **fkwargs):
        if cudnn.is_acceptable(input.data):
            func = CudnnRNN(*args, **kwargs)
        else:
            func = AutogradRNN(*args, **kwargs)

        # Hack for the tracer that allows us to represent RNNs as single
        # nodes and export them to ONNX in this form
        # Check the first argument explicitly to reduce the overhead of creating
        # the lambda. We need special handling here because the forward()
        # function gets reconstructed each and every time when RNN() is invoked
        # and we don't want to pay the cost of decorator invocation
        import torch
        if torch._C._jit_is_tracing(input):
            import torch.onnx.symbolic
            decorator = torch.onnx.symbolic_override_first_arg_based(
                torch.onnx.symbolic.RNN_symbolic_builder(*args, **kwargs))
            func = decorator(func)

        return func(input, *fargs, **fkwargs)

    return forward
