from collections import defaultdict

import numpy as np

import torch
import torch.nn as nn
import torch.nn.functional as F

CUDA_MAJOR = int(torch.version.cuda.split('.')[0])
CUDA_MINOR = int(torch.version.cuda.split('.')[1])


class ProjectedAdaptiveLogSoftmax(nn.Module):
    def __init__(self, n_token, d_embed, d_proj, cutoffs, div_val=1,
                 keep_order=False):
        super(ProjectedAdaptiveLogSoftmax, self).__init__()

        self.n_token = n_token
        self.d_embed = d_embed
        self.d_proj = d_proj

        self.cutoffs = cutoffs + [n_token]
        self.cutoff_ends = [0] + self.cutoffs
        self.div_val = div_val

        self.shortlist_size = self.cutoffs[0]
        self.n_clusters = len(self.cutoffs) - 1
        self.head_size = self.shortlist_size + self.n_clusters

        if self.n_clusters > 0:
            self.cluster_weight = nn.Parameter(
                torch.zeros(self.n_clusters, self.d_embed))
            self.cluster_bias = nn.Parameter(torch.zeros(self.n_clusters))

        self.out_layers = nn.ModuleList()
        self.out_projs = nn.ParameterList()

        if div_val == 1:
            for i in range(len(self.cutoffs)):
                if d_proj != d_embed:
                    self.out_projs.append(
                        nn.Parameter(torch.Tensor(d_proj, d_embed))
                    )
                else:
                    self.out_projs.append(None)

            self.out_layers.append(nn.Linear(d_embed, n_token))
        else:
            for i in range(len(self.cutoffs)):
                l_idx, r_idx = self.cutoff_ends[i], self.cutoff_ends[i+1]
                d_emb_i = d_embed // (div_val ** i)

                self.out_projs.append(
                    nn.Parameter(torch.Tensor(d_proj, d_emb_i))
                )

                self.out_layers.append(nn.Linear(d_emb_i, r_idx-l_idx))

        self.keep_order = keep_order

    def _compute_logit(self, hidden, weight, bias, proj):
        if proj is None:
            logit = F.linear(hidden, weight, bias=bias)
        else:
            # if CUDA_MAJOR <= 9 and CUDA_MINOR <= 1:
            proj_hid = F.linear(hidden, proj.t().contiguous())
            logit = F.linear(proj_hid, weight, bias=bias)

        return logit

    def forward(self, hidden, target, keep_order=False):
        # if keep_order is False, the (len * B) indices might not be preserved.
        # hidden shape: [len*B, d_proj]
        # target shape: [len*B]

        if hidden.size(0) != target.size(0):
            raise RuntimeError('Input and target should have the same size '
                               'in the batch dimension.')

        if self.n_clusters == 0:
            logit = self._compute_logit(hidden, self.out_layers[0].weight,
                                        self.out_layers[0].bias,
                                        self.out_projs[0])
            nll = -F.log_softmax(
                logit, dim=-1).gather(1, target.unsqueeze(1)).squeeze(1)
        else:
            # construct weights and biases
            weights, biases = [], []
            for i in range(len(self.cutoffs)):
                if self.div_val == 1:
                    l_idx, r_idx = self.cutoff_ends[i], self.cutoff_ends[i + 1]
                    weight_i = self.out_layers[0].weight[l_idx:r_idx]
                    bias_i = self.out_layers[0].bias[l_idx:r_idx]
                else:
                    weight_i = self.out_layers[i].weight
                    bias_i = self.out_layers[i].bias

                if i == 0:
                    weight_i = torch.cat(
                        [weight_i, self.cluster_weight], dim=0)
                    bias_i = torch.cat(
                        [bias_i, self.cluster_bias], dim=0)

                weights.append(weight_i)
                biases.append(bias_i)

            head_weight, head_bias, head_proj = (weights[0], biases[0],
                                                 self.out_projs[0])

            head_logit = self._compute_logit(
                hidden, head_weight, head_bias, head_proj)
            head_logprob = F.log_softmax(head_logit, dim=1)

            nll = torch.zeros_like(target,
                    dtype=hidden.dtype, device=hidden.device)

            offset = 0
            cutoff_values = [0] + self.cutoffs
            for i in range(len(cutoff_values) - 1):
                l_idx, r_idx = cutoff_values[i], cutoff_values[i + 1]

                mask_i = (target >= l_idx) & (target < r_idx)
                indices_i = mask_i.nonzero().squeeze()

                if indices_i.numel() == 0:
                    continue

                target_i = target.index_select(0, indices_i) - l_idx
                head_logprob_i = head_logprob.index_select(0, indices_i)

                if i == 0:
                    logprob_i = head_logprob_i.gather(
                        1, target_i[:,None]).squeeze(1)
                else:
                    weight_i, bias_i, proj_i = (weights[i], biases[i],
                                                self.out_projs[i])

                    hidden_i = hidden.index_select(0, indices_i)

                    tail_logit_i = self._compute_logit(
                        hidden_i, weight_i, bias_i, proj_i)
                    tail_logprob_i = F.log_softmax(tail_logit_i, dim=1)

                    logprob_i = head_logprob_i[:, -i] + tail_logprob_i.gather(
                        1, target_i[:,None]).squeeze(1)

                if (hasattr(self, 'keep_order')
                    and self.keep_order) or keep_order:
                    nll.index_copy_(0, indices_i, -logprob_i)
                else:
                    nll[offset:offset+logprob_i.size(0)].copy_(-logprob_i)

                offset += logprob_i.size(0)

        return nll
