import torch
import torch.nn as nn
from transformers import *

HIDDEN_OUTPUT_FEATURES = 768
TRAINED_WEIGHTS = 'bert-base-uncased'
NUM_CLASSES = 4  # no relation, fst hasFeature snd, snd hasFeature fst, siblings
HIDDEN_ENTITY_FEATURES = 6  # lower -> more general but less informative entity representations


class PairBertNet(nn.Module):

    def __init__(self):
        super(PairBertNet, self).__init__()
        # self.entity_fc1 = nn.Linear(HIDDEN_OUTPUT_FEATURES, HIDDEN_ENTITY_FEATURES)
        # self.entity_fc2 = nn.Linear(HIDDEN_ENTITY_FEATURES, HIDDEN_OUTPUT_FEATURES)
        config = BertConfig.from_pretrained(TRAINED_WEIGHTS)
        self.bert_base = BertModel.from_pretrained(TRAINED_WEIGHTS, config=config)
        self.fc = nn.Linear(HIDDEN_OUTPUT_FEATURES * 2, NUM_CLASSES)

    def forward(self, input_ids, attn_mask, fst_indices, snd_indices):
        # BERT
        bert_output, _ = self.bert_base(input_ids=input_ids, attention_mask=attn_mask)

        # max pooling at entity locations
        fst_pooled_output = PairBertNet.pooled_output(bert_output, fst_indices)
        snd_pooled_output = PairBertNet.pooled_output(bert_output, snd_indices)

        # concat pooled outputs from prod and feat entities
        combined = torch.cat((fst_pooled_output, snd_pooled_output), dim=1)

        # fc layer (softmax activation done in loss function)
        x = self.fc(combined)
        return x

    @staticmethod
    def pooled_output(bert_output, indices):
        outputs = torch.gather(bert_output, dim=1, index=indices)
        pooled_output, _ = torch.max(outputs, dim=1)
        return pooled_output