import torch.nn as nn

import pytorch_pretrained_bert as Bert

import numpy as np

import torch

class BertEmbeddings(nn.Module):

    """Construct the embeddings from word, segment, age

    """

    def __init__(self, config):

        super(BertEmbeddings, self).__init__()

        self.word_embeddings = nn.Embedding(config.vocab_size, config.hidden_size)

        self.segment_embeddings = nn.Embedding(config.seg_vocab_size, config.hidden_size)

        self.age_embeddings = nn.Embedding(config.age_vocab_size, config.hidden_size)

        self.posi_embeddings = nn.Embedding(config.max_position_embeddings, config.hidden_size). \

            from_pretrained(embeddings=self._init_posi_embedding(config.max_position_embeddings, config.hidden_size))

        self.LayerNorm = Bert.modeling.BertLayerNorm(config.hidden_size, eps=1e-12)

        self.dropout = nn.Dropout(config.hidden_dropout_prob)

    def forward(self, word_ids, age_ids=None, seg_ids=None, posi_ids=None, age=True):

        if seg_ids is None:

            seg_ids = torch.zeros_like(word_ids)

        if age_ids is None:

            age_ids = torch.zeros_like(word_ids)

        if posi_ids is None:

            posi_ids = torch.zeros_like(word_ids)

        word_embed = self.word_embeddings(word_ids)

        segment_embed = self.segment_embeddings(seg_ids)

        age_embed = self.age_embeddings(age_ids)

        posi_embeddings = self.posi_embeddings(posi_ids)

        if age:

            embeddings = word_embed + segment_embed + age_embed + posi_embeddings

        else:

            embeddings = word_embed + segment_embed + posi_embeddings

        embeddings = self.LayerNorm(embeddings)

        embeddings = self.dropout(embeddings)

        return embeddings

    def _init_posi_embedding(self, max_position_embedding, hidden_size):

        def even_code(pos, idx):

            return np.sin(pos / (10000 ** (2 * idx / hidden_size)))

        def odd_code(pos, idx):

            return np.cos(pos / (10000 ** (2 * idx / hidden_size)))

        # initialize position embedding table

        lookup_table = np.zeros((max_position_embedding, hidden_size), dtype=np.float32)

        # reset table parameters with hard encoding

        # set even dimension

        for pos in range(max_position_embedding):

            for idx in np.arange(0, hidden_size, step=2):

                lookup_table[pos, idx] = even_code(pos, idx)

        # set odd dimension

        for pos in range(max_position_embedding):

            for idx in np.arange(1, hidden_size, step=2):

                lookup_table[pos, idx] = odd_code(pos, idx)

        return torch.tensor(lookup_table)

class BertModel(Bert.modeling.BertPreTrainedModel):

    def __init__(self, config):

        super(BertModel, self).__init__(config)

        self.embeddings = BertEmbeddings(config=config)

        self.encoder = Bert.modeling.BertEncoder(config=config)

        self.pooler = Bert.modeling.BertPooler(config)

        self.apply(self.init_bert_weights)

    def forward(self, input_ids, age_ids=None, seg_ids=None, posi_ids=None, attention_mask=None,

                output_all_encoded_layers=True):

        if attention_mask is None:

            attention_mask = torch.ones_like(input_ids)

        if age_ids is None:

            age_ids = torch.zeros_like(input_ids)

        if seg_ids is None:

            seg_ids = torch.zeros_like(input_ids)

        if posi_ids is None:

            posi_ids = torch.zeros_like(input_ids)

        # We create a 3D attention mask from a 2D tensor mask.

        # Sizes are [batch_size, 1, 1, to_seq_length]

        # So we can broadcast to [batch_size, num_heads, from_seq_length, to_seq_length]

        # this attention mask is more simple than the triangular masking of causal attention

        # used in OpenAI GPT, we just need to prepare the broadcast dimension here.

        extended_attention_mask = attention_mask.unsqueeze(1).unsqueeze(2)

        # Since attention_mask is 1.0 for positions we want to attend and 0.0 for

        # masked positions, this operation will create a tensor which is 0.0 for

        # positions we want to attend and -10000.0 for masked positions.

        # Since we are adding it to the raw scores before the softmax, this is

        # effectively the same as removing these entirely.

        extended_attention_mask = extended_attention_mask.to(dtype=next(self.parameters()).dtype)  # fp16 compatibility

        extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0

        embedding_output = self.embeddings(input_ids, age_ids, seg_ids, posi_ids)

        encoded_layers = self.encoder(embedding_output,

                                      extended_attention_mask,

                                      output_all_encoded_layers=output_all_encoded_layers)

        sequence_output = encoded_layers[-1]

        pooled_output = self.pooler(sequence_output)

        if not output_all_encoded_layers:

            encoded_layers = encoded_layers[-1]

        return encoded_layers, pooled_output

class BertForMaskedLM(Bert.modeling.BertPreTrainedModel):

    def __init__(self, config):

        super(BertForMaskedLM, self).__init__(config)

        self.bert = BertModel(config)

        self.cls = Bert.modeling.BertOnlyMLMHead(config, self.bert.embeddings.word_embeddings.weight)

        self.apply(self.init_bert_weights)

    def forward(self, input_ids, age_ids=None, seg_ids=None, posi_ids=None, attention_mask=None, masked_lm_labels=None):

        sequence_output, _ = self.bert(input_ids, age_ids, seg_ids, posi_ids, attention_mask,

                                       output_all_encoded_layers=False)

        prediction_scores = self.cls(sequence_output)

        if masked_lm_labels is not None:

            loss_fct = nn.CrossEntropyLoss(ignore_index=-1)

            masked_lm_loss = loss_fct(prediction_scores.view(-1, self.config.vocab_size), masked_lm_labels.view(-1))

            return masked_lm_loss, prediction_scores.view(-1, self.config.vocab_size), masked_lm_labels.view(-1)

        else:

            return prediction_scores