# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

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

from fairseq.data import encoders


class RobertaHubInterface(nn.Module):
    """A simple PyTorch Hub interface to RoBERTa.

    Usage: https://github.com/pytorch/fairseq/tree/master/examples/roberta
    """

    def __init__(self, args, task, model):
        super().__init__()
        self.args = args
        self.task = task
        self.model = model

        self.bpe = encoders.build_bpe(args)

        # this is useful for determining the device
        self.register_buffer('_float_tensor', torch.tensor([0], dtype=torch.float))

    @property
    def device(self):
        return self._float_tensor.device

    def encode(self, sentence: str, *addl_sentences) -> torch.LongTensor:
        bpe_sentence = '<s> ' + self.bpe.encode(sentence) + ' </s>'
        for s in addl_sentences:
            bpe_sentence += ' </s> ' + self.bpe.encode(s) + ' </s>'
        tokens = self.task.source_dictionary.encode_line(bpe_sentence, append_eos=False)
        return tokens.long()

    def extract_features(self, tokens: torch.LongTensor, return_all_hiddens=False) -> torch.Tensor:
        if tokens.dim() == 1:
            tokens = tokens.unsqueeze(0)
        if tokens.size(-1) > self.model.max_positions():
            raise ValueError('tokens exceeds maximum length: {} > {}'.format(
                tokens.size(-1), self.model.max_positions()
            ))
        features, extra = self.model(
            tokens.to(device=self.device),
            features_only=True,
            return_all_hiddens=return_all_hiddens,
        )
        if return_all_hiddens:
            # convert from T x B x C -> B x T x C
            inner_states = extra['inner_states']
            return [inner_state.transpose(0, 1) for inner_state in inner_states]
        else:
            return features  # just the last layer's features

    def register_classification_head(
        self, name: str, num_classes: int = None, embedding_size: int = None, **kwargs
    ):
        self.model.register_classification_head(
            name, num_classes=num_classes, embedding_size=embedding_size, **kwargs
        )

    def predict(self, head: str, tokens: torch.LongTensor):
        features = self.extract_features(tokens)
        logits = self.model.classification_heads[head](features)
        return F.log_softmax(logits, dim=-1)
