import torch
from torch import Tensor
from torch import nn
from typing import Union, Tuple, List, Iterable, Dict
import os
import json


class WeightedLayerPooling(nn.Module):
    """
    Token embeddings are weighted mean of their different hidden layer representations
    """
    def __init__(self, word_embedding_dimension, num_hidden_layers: int = 12, layer_start: int = 4, layer_weights = None):
        super(WeightedLayerPooling, self).__init__()
        self.config_keys = ['word_embedding_dimension', 'layer_start', 'num_hidden_layers']
        self.word_embedding_dimension = word_embedding_dimension
        self.layer_start = layer_start
        self.num_hidden_layers = num_hidden_layers
        self.layer_weights = layer_weights if layer_weights is not None else nn.Parameter(torch.tensor([1] * (num_hidden_layers+1 - layer_start), dtype=torch.float))

    def forward(self, features: Dict[str, Tensor]):
        ft_all_layers = features['all_layer_embeddings']

        all_layer_embedding = torch.stack(ft_all_layers)
        all_layer_embedding = all_layer_embedding[self.layer_start:, :, :, :]  # Start from 4th layers output

        weight_factor = self.layer_weights.unsqueeze(-1).unsqueeze(-1).unsqueeze(-1).expand(all_layer_embedding.size())
        weighted_average = (weight_factor*all_layer_embedding).sum(dim=0) / self.layer_weights.sum()

        features.update({'token_embeddings': weighted_average})
        return features

    def get_word_embedding_dimension(self):
        return self.word_embedding_dimension

    def get_config_dict(self):
        return {key: self.__dict__[key] for key in self.config_keys}

    def save(self, output_path):
        with open(os.path.join(output_path, 'config.json'), 'w') as fOut:
            json.dump(self.get_config_dict(), fOut, indent=2)

        torch.save(self.state_dict(), os.path.join(output_path, 'pytorch_model.bin'))


    @staticmethod
    def load(input_path):
        with open(os.path.join(input_path, 'config.json')) as fIn:
            config = json.load(fIn)

        model = WeightedLayerPooling(**config)
        model.load_state_dict(torch.load(os.path.join(input_path, 'pytorch_model.bin'), map_location=torch.device('cpu')))
        return model