# --------------------------------------------------------
# The YiTrans End-to-End Speech Translation System for IWSLT 2022 Offline Shared Task (https://arxiv.org/abs/2206.05777)
# Github source: https://github.com/microsoft/SpeechT5/tree/main/YiTrans
# Copyright (c) 2022 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# Based on fairseq code bases
# https://github.com/facebookresearch/fairseq
# --------------------------------------------------------

"""
    Modified from https://github.com/facebookresearch/fairseq/blob/main/fairseq/tasks/translation.py
    Add custom lang_format in function load_langpair_dataset
"""

import itertools
import logging
import os

from fairseq.data import (
    AppendTokenDataset,
    LanguagePairDataset,
    PrependTokenDataset,
    StripTokenDataset,
    TruncateDataset,
    data_utils,
    indexed_dataset,
)

from yitrans_iwslt22.data.concat_dataset import ConcatDataset


EVAL_BLEU_ORDER = 4


logger = logging.getLogger(__name__)


def load_langpair_dataset(
    data_path,
    split,
    src,
    src_dict,
    tgt,
    tgt_dict,
    combine,
    dataset_impl,
    upsample_primary,
    left_pad_source,
    left_pad_target,
    max_source_positions,
    max_target_positions,
    prepend_bos=False,
    load_alignments=False,
    truncate_source=False,
    append_source_id=False,
    num_buckets=0,
    shuffle=True,
    pad_to_multiple=1,
    prepend_bos_src=None,
    lang_format="[{}]",
):
    def split_exists(split, src, tgt, lang, data_path):
        filename = os.path.join(data_path, "{}.{}-{}.{}".format(split, src, tgt, lang))
        return indexed_dataset.dataset_exists(filename, impl=dataset_impl)

    src_datasets = []
    tgt_datasets = []

    for k in itertools.count():
        split_k = split + (str(k) if k > 0 else "")

        # infer langcode
        if split_exists(split_k, src, tgt, src, data_path):
            prefix = os.path.join(data_path, "{}.{}-{}.".format(split_k, src, tgt))
        elif split_exists(split_k, tgt, src, src, data_path):
            prefix = os.path.join(data_path, "{}.{}-{}.".format(split_k, tgt, src))
        else:
            if k > 0:
                break
            else:
                raise FileNotFoundError(
                    "Dataset not found: {} ({})".format(split, data_path)
                )

        src_dataset = data_utils.load_indexed_dataset(
            prefix + src, src_dict, dataset_impl
        )
        if truncate_source:
            src_dataset = AppendTokenDataset(
                TruncateDataset(
                    StripTokenDataset(src_dataset, src_dict.eos()),
                    max_source_positions - 1,
                ),
                src_dict.eos(),
            )
        src_datasets.append(src_dataset)

        tgt_dataset = data_utils.load_indexed_dataset(
            prefix + tgt, tgt_dict, dataset_impl
        )
        if tgt_dataset is not None:
            tgt_datasets.append(tgt_dataset)

        logger.info(
            "{} {} {}-{} {} examples".format(
                data_path, split_k, src, tgt, len(src_datasets[-1])
            )
        )

        if not combine:
            break

    assert len(src_datasets) == len(tgt_datasets) or len(tgt_datasets) == 0

    if len(src_datasets) == 1:
        src_dataset = src_datasets[0]
        tgt_dataset = tgt_datasets[0] if len(tgt_datasets) > 0 else None
    else:
        sample_ratios = [1] * len(src_datasets)
        sample_ratios[0] = upsample_primary
        src_dataset = ConcatDataset(src_datasets, sample_ratios)
        if len(tgt_datasets) > 0:
            tgt_dataset = ConcatDataset(tgt_datasets, sample_ratios)
        else:
            tgt_dataset = None

    if prepend_bos:
        assert hasattr(src_dict, "bos_index") and hasattr(tgt_dict, "bos_index")
        src_dataset = PrependTokenDataset(src_dataset, src_dict.bos())
        if tgt_dataset is not None:
            tgt_dataset = PrependTokenDataset(tgt_dataset, tgt_dict.bos())
    elif prepend_bos_src is not None:
        logger.info(f"prepending src bos: {prepend_bos_src}")
        src_dataset = PrependTokenDataset(src_dataset, prepend_bos_src)

    eos = None
    if append_source_id:
        src_dataset = AppendTokenDataset(
            src_dataset, src_dict.index(lang_format.format(src))
        )
        if tgt_dataset is not None:
            tgt_dataset = AppendTokenDataset(
                tgt_dataset, tgt_dict.index(lang_format.format(tgt))
            )
        eos = tgt_dict.index(lang_format.format(tgt))

    align_dataset = None
    if load_alignments:
        align_path = os.path.join(data_path, "{}.align.{}-{}".format(split, src, tgt))
        if indexed_dataset.dataset_exists(align_path, impl=dataset_impl):
            align_dataset = data_utils.load_indexed_dataset(
                align_path, None, dataset_impl
            )

    tgt_dataset_sizes = tgt_dataset.sizes if tgt_dataset is not None else None
    return LanguagePairDataset(
        src_dataset,
        src_dataset.sizes,
        src_dict,
        tgt_dataset,
        tgt_dataset_sizes,
        tgt_dict,
        left_pad_source=left_pad_source,
        left_pad_target=left_pad_target,
        align_dataset=align_dataset,
        eos=eos,
        num_buckets=num_buckets,
        shuffle=shuffle,
        pad_to_multiple=pad_to_multiple,
    )
