# 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

from . import FairseqDataset


class ConcatSentencesDataset(FairseqDataset):

    def __init__(self, *datasets):
        super().__init__()
        self.datasets = datasets
        assert all(len(ds) == len(datasets[0]) for ds in datasets), \
            'datasets must have the same length'

    def __getitem__(self, index):
        return torch.cat([ds[index] for ds in self.datasets])

    def __len__(self):
        return len(self.datasets[0])

    def collater(self, samples):
        return self.datasets[0].collater(samples)

    @property
    def sizes(self):
        return sum(ds.sizes for ds in self.datasets)

    def num_tokens(self, index):
        return sum(ds.num_tokens(index) for ds in self.datasets)

    def size(self, index):
        return sum(ds.size(index) for ds in self.datasets)

    def ordered_indices(self):
        return self.datasets[0].ordered_indices()

    @property
    def supports_prefetch(self):
        return any(
            getattr(ds, 'supports_prefetch', False) for ds in self.datasets
        )

    def prefetch(self, indices):
        for ds in self.datasets:
            if getattr(ds, 'supports_prefetch', False):
                ds.prefetch(indices)
