# coding=utf-8
# Copyright 2022 The TensorFlow Datasets Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""WMT: Translate dataset."""

import codecs
import functools
import gzip
import itertools
import os
import re
import xml.etree.cElementTree as ElementTree

from absl import logging
import six
import tensorflow as tf
import tensorflow_datasets.public_api as tfds

_DESCRIPTION = """\
Translate dataset based on the data from statmt.org.

Versions exists for the different years using a combination of multiple data
sources. The base `wmt_translate` allows you to create your own config to choose
your own data/language pair by creating a custom `tfds.translate.wmt.WmtConfig`.

```
config = tfds.translate.wmt.WmtConfig(
    version="0.0.1",
    language_pair=("fr", "de"),
    subsets={
        tfds.Split.TRAIN: ["commoncrawl_frde"],
        tfds.Split.VALIDATION: ["euelections_dev2019"],
    },
)
builder = tfds.builder("wmt_translate", config=config)
```

"""

CWMT_SUBSET_NAMES = [
    "casia2015", "casict2011", "casict2015", "datum2015", "datum2017", "neu2017"
]


class SubDataset(object):
  """Class to keep track of information on a sub-dataset of WMT."""

  def __init__(self, name, target, sources, url, path, manual_dl_files=None):
    """Sub-dataset of WMT.

    Args:
      name: `string`, a unique dataset identifier.
      target: `string`, the target language code.
      sources: `set<string>`, the set of source language codes.
      url: `string` or `(string, string)`, URL(s) or URL template(s) specifying
        where to download the raw data from. If two strings are provided, the
        first is used for the source language and the second for the target.
        Template strings can either contain '{src}' placeholders that will be
        filled in with the source language code, '{0}' and '{1}' placeholders
        that will be filled in with the source and target language codes in
        alphabetical order, or all 3.
      path: `string` or `(string, string)`, path(s) or path template(s)
        specifing the path to the raw data relative to the root of the
        downloaded archive. If two strings are provided, the dataset is assumed
        to be made up of parallel text files, the first being the source and the
        second the target. If one string is provided, both languages are assumed
        to be stored within the same file and the extension is used to determine
        how to parse it. Template strings should be formatted the same as in
        `url`.
      manual_dl_files: `<list>(string)` (optional), the list of files that must
        be manually downloaded to the data directory.
    """
    self._paths = (path,) if isinstance(path, six.string_types) else path
    self._urls = (url,) if isinstance(url, six.string_types) else url
    self._manual_dl_files = manual_dl_files if manual_dl_files else []
    self.name = name
    self.target = target
    self.sources = set(sources)

  def _inject_language(self, src, strings):
    """Injects languages into (potentially) template strings."""
    if src not in self.sources:
      raise ValueError("Invalid source for '{0}': {1}".format(self.name, src))

    def _format_string(s):
      if "{0}" in s and "{1}" and "{src}" in s:
        return s.format(*sorted([src, self.target]), src=src)
      elif "{0}" in s and "{1}" in s:
        return s.format(*sorted([src, self.target]))
      elif "{src}" in s:
        return s.format(src=src)
      else:
        return s

    return [_format_string(s) for s in strings]

  def get_url(self, src):
    return self._inject_language(src, self._urls)

  def get_manual_dl_files(self, src):
    return self._inject_language(src, self._manual_dl_files)

  def get_path(self, src):
    return self._inject_language(src, self._paths)


# Subsets used in the training sets for various years of WMT.
_TRAIN_SUBSETS = [
    # pylint:disable=line-too-long
    SubDataset(
        name="commoncrawl",
        target="en",  # fr-de pair in commoncrawl_frde
        sources={"cs", "de", "es", "fr", "ru"},
        url="http://www.statmt.org/wmt13/training-parallel-commoncrawl.tgz",
        path=("commoncrawl.{src}-en.{src}", "commoncrawl.{src}-en.en")),
    SubDataset(
        name="commoncrawl_frde",
        target="de",
        sources={"fr"},
        url=(
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/commoncrawl.fr.gz",
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/commoncrawl.de.gz"
        ),
        path=("", "")),
    SubDataset(
        name="czeng_10",
        target="en",
        sources={"cs"},
        url="http://ufal.mff.cuni.cz/czeng/czeng10",
        manual_dl_files=["data-plaintext-format.%d.tar" % i for i in range(10)],
        # Each tar contains multiple files, which we process specially in
        # _parse_czeng.
        path=("data.plaintext-format/??train.gz",) * 10),
    SubDataset(
        name="czeng_16pre",
        target="en",
        sources={"cs"},
        url="http://ufal.mff.cuni.cz/czeng/czeng16pre",
        manual_dl_files=["czeng16pre.deduped-ignoring-sections.txt.gz"],
        path=""),
    SubDataset(
        name="czeng_16",
        target="en",
        sources={"cs"},
        url="http://ufal.mff.cuni.cz/czeng",
        manual_dl_files=["data-plaintext-format.%d.tar" % i for i in range(10)],
        # Each tar contains multiple files, which we process specially in
        # _parse_czeng.
        path=("data.plaintext-format/??train.gz",) * 10),
    SubDataset(
        # This dataset differs from the above in the filtering that is applied
        # during parsing.
        name="czeng_17",
        target="en",
        sources={"cs"},
        url="http://ufal.mff.cuni.cz/czeng",
        manual_dl_files=["data-plaintext-format.%d.tar" % i for i in range(10)],
        # Each tar contains multiple files, which we process specially in
        # _parse_czeng.
        path=("data.plaintext-format/??train.gz",) * 10),
    SubDataset(
        name="dcep_v1",
        target="en",
        sources={"lv"},
        url="http://data.statmt.org/wmt17/translation-task/dcep.lv-en.v1.tgz",
        path=("dcep.en-lv/dcep.lv", "dcep.en-lv/dcep.en")),
    SubDataset(
        name="europarl_v7",
        target="en",
        sources={"cs", "de", "es", "fr"},
        url="http://www.statmt.org/wmt13/training-parallel-europarl-v7.tgz",
        path=("training/europarl-v7.{src}-en.{src}",
              "training/europarl-v7.{src}-en.en")),
    SubDataset(
        name="europarl_v7_frde",
        target="de",
        sources={"fr"},
        url=(
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/europarl-v7.fr.gz",
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/europarl-v7.de.gz"
        ),
        path=("", "")),
    SubDataset(
        name="europarl_v8_18",
        target="en",
        sources={"et", "fi"},
        url="http://data.statmt.org/wmt18/translation-task/training-parallel-ep-v8.tgz",
        path=("training/europarl-v8.{src}-en.{src}",
              "training/europarl-v8.{src}-en.en")),
    SubDataset(
        name="europarl_v8_16",
        target="en",
        sources={"fi", "ro"},
        url="http://data.statmt.org/wmt16/translation-task/training-parallel-ep-v8.tgz",
        path=("training-parallel-ep-v8/europarl-v8.{src}-en.{src}",
              "training-parallel-ep-v8/europarl-v8.{src}-en.en")),
    SubDataset(
        name="europarl_v9",
        target="en",
        sources={"cs", "de", "fi", "lt"},
        url="http://www.statmt.org/europarl/v9/training/europarl-v9.{src}-en.tsv.gz",
        path=""),
    SubDataset(
        name="gigafren",
        target="en",
        sources={"fr"},
        url="http://www.statmt.org/wmt10/training-giga-fren.tar",
        path=("giga-fren.release2.fixed.fr.gz",
              "giga-fren.release2.fixed.en.gz")),
    SubDataset(
        name="hindencorp_01",
        target="en",
        sources={"hi"},
        url="http://ufallab.ms.mff.cuni.cz/~bojar/hindencorp",
        manual_dl_files=["hindencorp0.1.gz"],
        path=""),
    SubDataset(
        name="leta_v1",
        target="en",
        sources={"lv"},
        url="http://data.statmt.org/wmt17/translation-task/leta.v1.tgz",
        path=("LETA-lv-en/leta.lv", "LETA-lv-en/leta.en")),
    SubDataset(
        name="multiun",
        target="en",
        sources={"es", "fr"},
        url="http://www.statmt.org/wmt13/training-parallel-un.tgz",
        path=("un/undoc.2000.{src}-en.{src}", "un/undoc.2000.{src}-en.en")),
    SubDataset(
        name="newscommentary_v8",
        target="en",
        sources={"cs", "de", "fr", "es", "ru"},
        url="http://www.statmt.org/wmt13/training-parallel-nc-v8.tgz",
        path=("training/news-commentary-v8.{src}-en.{src}",
              "training/news-commentary-v8.{src}-en.en")),
    SubDataset(
        name="newscommentary_v9",
        target="en",
        sources={"cs", "de", "fr", "ru"},
        url="http://www.statmt.org/wmt14/training-parallel-nc-v9.tgz",
        path=("training/news-commentary-v9.{src}-en.{src}",
              "training/news-commentary-v9.{src}-en.en")),
    SubDataset(
        name="newscommentary_v10",
        target="en",
        sources={"cs", "de", "fr", "ru"},
        url="http://www.statmt.org/wmt15/training-parallel-nc-v10.tgz",
        path=("news-commentary-v10.{src}-en.{src}",
              "news-commentary-v10.{src}-en.en")),
    SubDataset(
        name="newscommentary_v11",
        target="en",
        sources={"cs", "de", "ru"},
        url="http://data.statmt.org/wmt16/translation-task/training-parallel-nc-v11.tgz",
        path=("training-parallel-nc-v11/news-commentary-v11.{src}-en.{src}",
              "training-parallel-nc-v11/news-commentary-v11.{src}-en.en")),
    SubDataset(
        name="newscommentary_v12",
        target="en",
        sources={"cs", "de", "ru", "zh"},
        url="http://data.statmt.org/wmt17/translation-task/training-parallel-nc-v12.tgz",
        path=("training/news-commentary-v12.{src}-en.{src}",
              "training/news-commentary-v12.{src}-en.en")),
    SubDataset(
        name="newscommentary_v13",
        target="en",
        sources={"cs", "de", "ru", "zh"},
        url="http://data.statmt.org/wmt18/translation-task/training-parallel-nc-v13.tgz",
        path=("training-parallel-nc-v13/news-commentary-v13.{src}-en.{src}",
              "training-parallel-nc-v13/news-commentary-v13.{src}-en.en")),
    SubDataset(
        name="newscommentary_v14",
        target="en",  # fr-de pair in newscommentary_v14_frde
        sources={"cs", "de", "kk", "ru", "zh"},
        url="http://data.statmt.org/news-commentary/v14/training/news-commentary-v14.{0}-{1}.tsv.gz",
        path=""),
    SubDataset(
        name="newscommentary_v14_frde",
        target="de",
        sources={"fr"},
        url="http://data.statmt.org/news-commentary/v14/training/news-commentary-v14.de-fr.tsv.gz",
        path=""),
    SubDataset(
        name="onlinebooks_v1",
        target="en",
        sources={"lv"},
        url="http://data.statmt.org/wmt17/translation-task/books.lv-en.v1.tgz",
        path=("farewell/farewell.lv", "farewell/farewell.en")),
    SubDataset(
        name="paracrawl_v1",
        target="en",
        sources={"cs", "de", "et", "fi", "ru"},
        url="https://s3.amazonaws.com/web-language-models/paracrawl/release1/paracrawl-release1.en-{src}.zipporah0-dedup-clean.tgz",
        path=("paracrawl-release1.en-{src}.zipporah0-dedup-clean.{src}",
              "paracrawl-release1.en-{src}.zipporah0-dedup-clean.en")),
    SubDataset(
        name="paracrawl_v1_ru",
        target="en",
        sources={"ru"},
        url="https://s3.amazonaws.com/web-language-models/paracrawl/release1/paracrawl-release1.en-ru.zipporah0-dedup-clean.tgz",
        path=("paracrawl-release1.en-ru.zipporah0-dedup-clean.ru",
              "paracrawl-release1.en-ru.zipporah0-dedup-clean.en")),
    SubDataset(
        name="paracrawl_v3",
        target="en",  # fr-de pair in paracrawl_v3_frde
        sources={"cs", "de", "fi", "lt"},
        url="https://s3.amazonaws.com/web-language-models/paracrawl/release3/en-{src}.bicleaner07.tmx.gz",
        path=""),
    SubDataset(
        name="paracrawl_v3_frde",
        target="de",
        sources={"fr"},
        url=(
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/de-fr.bicleaner07.de.gz",
            "http://data.statmt.org/wmt19/translation-task/fr-de/bitexts/de-fr.bicleaner07.fr.gz"
        ),
        path=("", "")),
    SubDataset(
        name="rapid_2016",
        target="en",
        sources={"de", "et", "fi"},
        url="http://data.statmt.org/wmt18/translation-task/rapid2016.tgz",
        path=("rapid2016.{0}-{1}.{src}", "rapid2016.{0}-{1}.en")),
    SubDataset(
        name="rapid_2016_ltfi",
        target="en",
        sources={"fi", "lt"},
        url="https://tilde-model.s3-eu-west-1.amazonaws.com/rapid2016.en-{src}.tmx.zip",
        path="rapid2016.en-{src}.tmx"),
    SubDataset(
        name="rapid_2019",
        target="en",
        sources={"de"},
        url="https://s3-eu-west-1.amazonaws.com/tilde-model/rapid2019.de-en.zip",
        path=("rapid2019.de-en.de", "rapid2019.de-en.en")),
    SubDataset(
        name="setimes_2",
        target="en",
        sources={"ro", "tr"},
        url="http://opus.nlpl.eu/download.php?f=SETIMES/v2/tmx/en-{src}.tmx.gz",
        path=""),
    SubDataset(
        name="uncorpus_v1",
        target="en",
        sources={"ru", "zh"},
        url="https://storage.googleapis.com/tfds-data/downloads/uncorpus/UNv1.0.en-{src}.tar.gz",
        path=("en-{src}/UNv1.0.en-{src}.{src}", "en-{src}/UNv1.0.en-{src}.en")),
    SubDataset(
        name="wikiheadlines_fi",
        target="en",
        sources={"fi"},
        url="http://www.statmt.org/wmt15/wiki-titles.tgz",
        path="wiki/fi-en/titles.fi-en"),
    SubDataset(
        name="wikiheadlines_hi",
        target="en",
        sources={"hi"},
        url="http://www.statmt.org/wmt14/wiki-titles.tgz",
        path="wiki/hi-en/wiki-titles.hi-en"),
    SubDataset(
        # Verified that wmt13, wmt14 and wmt15 files are identical.
        name="wikiheadlines_ru",
        target="en",
        sources={"ru"},
        url="http://www.statmt.org/wmt15/wiki-titles.tgz",
        path="wiki/ru-en/wiki.ru-en"),
    SubDataset(
        name="wikititles_v1",
        target="en",
        sources={"cs", "de", "fi", "gu", "kk", "lt", "ru", "zh"},
        url="http://data.statmt.org/wikititles/v1/wikititles-v1.{src}-en.tsv.gz",
        path=""),
    SubDataset(
        name="yandexcorpus",
        target="en",
        sources={"ru"},
        url="https://translate.yandex.ru/corpus?lang=en",
        manual_dl_files=["1mcorpus.zip"],
        path=("corpus.en_ru.1m.ru", "corpus.en_ru.1m.en")),
    # pylint:enable=line-too-long
] + [
    SubDataset(  # pylint:disable=g-complex-comprehension
        name=ss,
        target="en",
        sources={"zh"},
        url="ftp://cwmt-wmt:cwmt-wmt@nlp.nju.edu.cn/parallel/%s.zip" % ss,
        path=("%s/*_c[hn].txt" % ss, "%s/*_en.txt" % ss))
    for ss in CWMT_SUBSET_NAMES
]

_DEV_SUBSETS = [
    SubDataset(
        name="euelections_dev2019",
        target="de",
        sources={"fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/euelections_dev2019.fr-de.src.fr",
              "dev/euelections_dev2019.fr-de.tgt.de")),
    SubDataset(
        name="newsdev2014",
        target="en",
        sources={"hi"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2014.hi", "dev/newsdev2014.en")),
    SubDataset(
        name="newsdev2015",
        target="en",
        sources={"fi"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2015-fien-src.{src}.sgm",
              "dev/newsdev2015-fien-ref.en.sgm")),
    SubDataset(
        name="newsdiscussdev2015",
        target="en",
        sources={"ro", "tr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdiscussdev2015-{src}en-src.{src}.sgm",
              "dev/newsdiscussdev2015-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdev2016",
        target="en",
        sources={"ro", "tr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2016-{src}en-src.{src}.sgm",
              "dev/newsdev2016-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdev2017",
        target="en",
        sources={"lv", "zh"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2017-{src}en-src.{src}.sgm",
              "dev/newsdev2017-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdev2018",
        target="en",
        sources={"et"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2018-{src}en-src.{src}.sgm",
              "dev/newsdev2018-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdev2019",
        target="en",
        sources={"gu", "kk", "lt"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdev2019-{src}en-src.{src}.sgm",
              "dev/newsdev2019-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdiscussdev2015",
        target="en",
        sources={"fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdiscussdev2015-{src}en-src.{src}.sgm",
              "dev/newsdiscussdev2015-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdiscusstest2015",
        target="en",
        sources={"fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdiscusstest2015-{src}en-src.{src}.sgm",
              "dev/newsdiscusstest2015-{src}en-ref.en.sgm")),
    SubDataset(
        name="newssyscomb2009",
        target="en",
        sources={"cs", "de", "es", "fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newssyscomb2009.{src}", "dev/newssyscomb2009.en")),
    SubDataset(
        name="newstest2008",
        target="en",
        sources={"cs", "de", "es", "fr", "hu"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/news-test2008.{src}", "dev/news-test2008.en")),
    SubDataset(
        name="newstest2009",
        target="en",
        sources={"cs", "de", "es", "fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2009.{src}", "dev/newstest2009.en")),
    SubDataset(
        name="newstest2010",
        target="en",
        sources={"cs", "de", "es", "fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2010.{src}", "dev/newstest2010.en")),
    SubDataset(
        name="newstest2011",
        target="en",
        sources={"cs", "de", "es", "fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2011.{src}", "dev/newstest2011.en")),
    SubDataset(
        name="newstest2012",
        target="en",
        sources={"cs", "de", "es", "fr", "ru"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2012.{src}", "dev/newstest2012.en")),
    SubDataset(
        name="newstest2013",
        target="en",
        sources={"cs", "de", "es", "fr", "ru"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2013.{src}", "dev/newstest2013.en")),
    SubDataset(
        name="newstest2014",
        target="en",
        sources={"cs", "de", "es", "fr", "hi", "ru"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2014-{src}en-src.{src}.sgm",
              "dev/newstest2014-{src}en-ref.en.sgm")),
    SubDataset(
        name="newstest2015",
        target="en",
        sources={"cs", "de", "fi", "ru"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2015-{src}en-src.{src}.sgm",
              "dev/newstest2015-{src}en-ref.en.sgm")),
    SubDataset(
        name="newsdiscusstest2015",
        target="en",
        sources={"fr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newsdiscusstest2015-{src}en-src.{src}.sgm",
              "dev/newsdiscusstest2015-{src}en-ref.en.sgm")),
    SubDataset(
        name="newstest2016",
        target="en",
        sources={"cs", "de", "fi", "ro", "ru", "tr"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2016-{src}en-src.{src}.sgm",
              "dev/newstest2016-{src}en-ref.en.sgm")),
    SubDataset(
        name="newstestB2016",
        target="en",
        sources={"fi"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstestB2016-enfi-ref.{src}.sgm",
              "dev/newstestB2016-enfi-src.en.sgm")),
    SubDataset(
        name="newstest2017",
        target="en",
        sources={"cs", "de", "fi", "lv", "ru", "tr", "zh"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2017-{src}en-src.{src}.sgm",
              "dev/newstest2017-{src}en-ref.en.sgm")),
    SubDataset(
        name="newstestB2017",
        target="en",
        sources={"fi"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstestB2017-fien-src.fi.sgm",
              "dev/newstestB2017-fien-ref.en.sgm")),
    SubDataset(
        name="newstest2018",
        target="en",
        sources={"cs", "de", "et", "fi", "ru", "tr", "zh"},
        url="http://data.statmt.org/wmt19/translation-task/dev.tgz",
        path=("dev/newstest2018-{src}en-src.{src}.sgm",
              "dev/newstest2018-{src}en-ref.en.sgm")),
]

DATASET_MAP = {ds.name: ds for ds in _TRAIN_SUBSETS + _DEV_SUBSETS}

_CZENG17_FILTER = SubDataset(
    name="czeng17_filter",
    target="en",
    sources={"cs"},
    url="http://ufal.mff.cuni.cz/czeng/download.php?f=convert_czeng16_to_17.pl.zip",
    path="convert_czeng16_to_17.pl")


class WmtConfig(tfds.core.BuilderConfig):
  """BuilderConfig for WMT."""

  def __init__(self,
               *,
               url=None,
               citation=None,
               description=None,
               language_pair=(None, None),
               subsets=None,
               **kwargs):
    """BuilderConfig for WMT.

    Args:
      url: The reference URL for the dataset.
      citation: The paper citation for the dataset.
      description: The description of the dataset.
      language_pair: pair of languages that will be used for translation. Should
                 contain 2 letter coded strings. For example: ("en", "de").
      subsets: Dict[split, list[str]]. List of the subset to use for each of the
        split. Note that WMT subclasses overwrite this parameter.
      **kwargs: keyword arguments forwarded to super.
    """
    name = "%s-%s" % (language_pair[0], language_pair[1])
    if "name" in kwargs:  # Add name suffix for custom configs
      name += "." + kwargs.pop("name")

    super(WmtConfig, self).__init__(
        name=name, description=description, **kwargs)

    self.url = url or "http://www.statmt.org"
    self.citation = citation
    self.language_pair = language_pair
    self.subsets = subsets


class WmtTranslate(tfds.core.GeneratorBasedBuilder):
  """WMT translation dataset."""

  MANUAL_DOWNLOAD_INSTRUCTIONS = """\
  Some of the wmt configs here, require a manual download.
  Please look into wmt.py to see the exact path (and file name) that has to
  be downloaded.
  """

  def __init__(self, *args, **kwargs):
    if type(self) == WmtTranslate and "config" not in kwargs:  # pylint: disable=unidiomatic-typecheck
      raise ValueError(
          "The raw `wmt_translate` can only be instantiated with the config "
          "kwargs. You may want to use one of the `wmtYY_translate` "
          "implementation instead to get the WMT dataset for a specific year.")
    super(WmtTranslate, self).__init__(*args, **kwargs)

  @property
  def _subsets(self):
    """Subsets that make up each split of the dataset."""
    return self.builder_config.subsets

  @property
  def subsets(self):
    """Subsets that make up each split of the dataset for the language pair."""
    source, target = self.builder_config.language_pair
    filtered_subsets = {}
    for split, ss_names in self._subsets.items():
      filtered_subsets[split] = []
      for ss_name in ss_names:
        ds = DATASET_MAP[ss_name]
        if ds.target != target or source not in ds.sources:
          logging.info(
              "Skipping sub-dataset that does not include language pair: %s",
              ss_name)
        else:
          filtered_subsets[split].append(ss_name)
    logging.info("Using sub-datasets: %s", filtered_subsets)
    return filtered_subsets

  def _info(self):
    src, target = self.builder_config.language_pair
    return tfds.core.DatasetInfo(
        builder=self,
        description=_DESCRIPTION,
        features=tfds.features.Translation(
            languages=self.builder_config.language_pair,),
        supervised_keys=(src, target),
        homepage=self.builder_config.url,
        citation=self.builder_config.citation,
    )

  def _split_generators(self, dl_manager):
    source, _ = self.builder_config.language_pair

    def _check_manual_files(ds):
      """Verifies the manual files are downloaded for the given sub-dataset."""
      manual_dl_files = ds.get_manual_dl_files(source)
      manual_paths = []
      for fname in manual_dl_files:
        manual_path = os.path.join(dl_manager.manual_dir, fname)
        if not tf.io.gfile.exists(manual_path):
          raise AssertionError(
              "For {0}, you must manually download the following file(s) "
              "from {1} and place them in {2}: {3}".format(
                  ds.name, ds.get_url(source), dl_manager.manual_dir,
                  ", ".join(manual_dl_files)))
        manual_paths.append(manual_path)
      return manual_paths

    manual_paths = {}
    urls_to_download = {}
    for ss_name in itertools.chain.from_iterable(self.subsets.values()):
      if ss_name == "czeng_17":
        # CzEng1.7 is CzEng1.6 with some blocks filtered out. We must download
        # the filtering script so we can parse out which blocks need to be
        # removed.
        urls_to_download[_CZENG17_FILTER.name] = _CZENG17_FILTER.get_url(source)
      ds = DATASET_MAP[ss_name]
      if ds.get_manual_dl_files(source):
        manual_paths[ss_name] = _check_manual_files(ds)
      else:
        urls_to_download[ss_name] = ds.get_url(source)

    # Download and extract files from URLs.
    downloaded_files = dl_manager.download_and_extract(urls_to_download)
    # Extract manually downloaded files.
    manual_files = dl_manager.extract(manual_paths)

    manual_files = tf.nest.map_structure(os.fspath, manual_files)
    downloaded_files = tf.nest.map_structure(os.fspath, downloaded_files)

    extraction_map = dict(downloaded_files, **manual_files)

    return [
        tfds.core.SplitGenerator(  # pylint:disable=g-complex-comprehension
            name=split,
            gen_kwargs={
                "split_subsets": split_subsets,
                "extraction_map": extraction_map
            }) for split, split_subsets in self.subsets.items()
    ]

  def _generate_examples(self, split_subsets, extraction_map):
    """Returns the examples in the raw (text) form."""
    source, _ = self.builder_config.language_pair

    def _get_local_paths(ds, extract_dirs):
      rel_paths = ds.get_path(source)
      if len(extract_dirs) == 1:
        extract_dirs = extract_dirs * len(rel_paths)
      return [
          os.path.join(ex_dir, rel_path) if rel_path else ex_dir
          for ex_dir, rel_path in zip(extract_dirs, rel_paths)
      ]

    for ss_name in split_subsets:
      logging.info("Generating examples from: %s", ss_name)
      ds = DATASET_MAP[ss_name]
      extract_dirs = extraction_map[ss_name]
      files = _get_local_paths(ds, extract_dirs)
      if ss_name.startswith("czeng"):
        if ss_name.endswith("16pre"):
          sub_generator = functools.partial(
              _parse_tsv, language_pair=("en", "cs"))
        elif ss_name.endswith("17"):
          filter_path = _get_local_paths(
              _CZENG17_FILTER, extraction_map[_CZENG17_FILTER.name])[0]
          sub_generator = functools.partial(
              _parse_czeng, filter_path=filter_path)
        else:
          sub_generator = _parse_czeng
      elif ss_name == "hindencorp_01":
        sub_generator = _parse_hindencorp
      elif len(files) == 2:
        if ss_name.endswith("_frde"):
          sub_generator = _parse_frde_bitext
        else:
          sub_generator = _parse_parallel_sentences
      elif len(files) == 1:
        fname = files[0]
        # Note: Due to formatting used by `download_manager`, the file
        # extension may not be at the end of the file path.
        if ".tsv" in fname:
          sub_generator = _parse_tsv
        elif ss_name.startswith("newscommentary_v14"):
          sub_generator = functools.partial(
              _parse_tsv, language_pair=self.builder_config.language_pair)
        elif "tmx" in fname:
          sub_generator = _parse_tmx
        elif ss_name.startswith("wikiheadlines"):
          sub_generator = _parse_wikiheadlines
        else:
          raise ValueError("Unsupported file format: %s" % fname)
      else:
        raise ValueError("Invalid number of files: %d" % len(files))

      for sub_key, ex in sub_generator(*files):
        if not all(ex.values()):
          continue
        # TODO(adarob): Add subset feature.
        # ex["subset"] = subset
        key = "{}/{}".format(ss_name, sub_key)
        yield key, ex


def _parse_parallel_sentences(f1, f2):
  """Returns examples from parallel SGML or text files, which may be gzipped."""

  def _parse_text(path):
    """Returns the sentences from a single text file, which may be gzipped."""
    split_path = path.split(".")

    if split_path[-1] == "gz":
      lang = split_path[-2]
      with tf.io.gfile.GFile(path, "rb") as f, gzip.GzipFile(fileobj=f) as g:
        return g.read().decode("utf-8").split("\n"), lang

    if split_path[-1] == "txt":
      # CWMT
      lang = split_path[-2].split("_")[-1]
      lang = "zh" if lang in ("ch", "cn") else lang
    else:
      lang = split_path[-1]
    with tf.io.gfile.GFile(path) as f:
      return f.read().split("\n"), lang

  def _parse_sgm(path):
    """Returns sentences from a single SGML file."""
    lang = path.split(".")[-2]
    sentences = []
    # Note: We can't use the XML parser since some of the files are badly
    # formatted.
    seg_re = re.compile(r"<seg id=\"\d+\">(.*)</seg>")
    with tf.io.gfile.GFile(path) as f:
      for line in f:
        seg_match = re.match(seg_re, line)
        if seg_match:
          assert len(seg_match.groups()) == 1
          sentences.append(seg_match.groups()[0])
    return sentences, lang

  parse_file = _parse_sgm if f1.endswith(".sgm") else _parse_text

  # Some datasets (e.g., CWMT) contain multiple parallel files specified with
  # a wildcard. We sort both sets to align them and parse them one by one.
  f1_files = tf.io.gfile.glob(f1)
  f2_files = tf.io.gfile.glob(f2)

  assert f1_files and f2_files, "No matching files found: %s, %s." % (f1, f2)
  assert len(f1_files) == len(f2_files), (
      "Number of files do not match: %d vs %d for %s vs %s." %
      (len(f1_files), len(f2_files), f1, f2))

  for f_id, (f1_i, f2_i) in enumerate(zip(sorted(f1_files), sorted(f2_files))):
    l1_sentences, l1 = parse_file(f1_i)
    l2_sentences, l2 = parse_file(f2_i)

    assert len(l1_sentences) == len(l2_sentences), (
        "Sizes do not match: %d vs %d for %s vs %s." %
        (len(l1_sentences), len(l2_sentences), f1_i, f2_i))

    for line_id, (s1, s2) in enumerate(zip(l1_sentences, l2_sentences)):
      key = "{}/{}".format(f_id, line_id)
      yield key, {l1: s1, l2: s2}


def _parse_frde_bitext(fr_path, de_path):
  with tf.io.gfile.GFile(fr_path) as f:
    fr_sentences = f.read().split("\n")
  with tf.io.gfile.GFile(de_path) as f:
    de_sentences = f.read().split("\n")
  assert len(fr_sentences) == len(de_sentences), (
      "Sizes do not match: %d vs %d for %s vs %s." %
      (len(fr_sentences), len(de_sentences), fr_path, de_path))
  for line_id, (s1, s2) in enumerate(zip(fr_sentences, de_sentences)):
    yield line_id, {"fr": s1, "de": s2}


def _parse_tmx(path):
  """Generates examples from TMX file."""

  def _get_tuv_lang(tuv):
    for k, v in tuv.items():
      if k.endswith("}lang"):
        return v
    raise AssertionError("Language not found in `tuv` attributes.")

  def _get_tuv_seg(tuv):
    segs = tuv.findall("seg")
    assert len(segs) == 1, "Invalid number of segments: %d" % len(segs)
    return segs[0].text

  with tf.io.gfile.GFile(path, "rb") as f:
    if six.PY3:
      # Workaround due to: https://github.com/tensorflow/tensorflow/issues/33563
      utf_f = codecs.getreader("utf-8")(f)
    else:
      utf_f = f
    for line_id, (_, elem) in enumerate(ElementTree.iterparse(utf_f)):  # pytype: disable=wrong-arg-types
      if elem.tag == "tu":
        yield line_id, {
            _get_tuv_lang(tuv): _get_tuv_seg(tuv)
            for tuv in elem.iterfind("tuv")
        }
        elem.clear()


def _parse_tsv(path, language_pair=None):
  """Generates examples from TSV file."""
  if language_pair is None:
    lang_match = re.match(r".*\.([a-z][a-z])-([a-z][a-z])\.tsv", path)
    assert lang_match is not None, "Invalid TSV filename: %s" % path
    l1, l2 = lang_match.groups()
  else:
    l1, l2 = language_pair
  with tf.io.gfile.GFile(path) as f:
    for j, line in enumerate(f):
      cols = line.split("\t")
      if len(cols) != 2:
        logging.warning("Skipping line %d in TSV (%s) with %d != 2 columns.", j,
                        path, len(cols))
        continue
      s1, s2 = cols
      yield j, {l1: s1.strip(), l2: s2.strip()}


def _parse_wikiheadlines(path):
  """Generates examples from Wikiheadlines dataset file."""
  lang_match = re.match(r".*\.([a-z][a-z])-([a-z][a-z])$", path)
  assert lang_match is not None, "Invalid Wikiheadlines filename: %s" % path
  l1, l2 = lang_match.groups()
  with tf.io.gfile.GFile(path) as f:
    for line_id, line in enumerate(f):
      s1, s2 = line.split("|||")
      yield line_id, {l1: s1.strip(), l2: s2.strip()}


def _parse_czeng(*paths, **kwargs):
  """Generates examples from CzEng v1.6, with optional filtering for v1.7."""
  filter_path = kwargs.get("filter_path", None)
  if filter_path: