#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright (C) 2015 Dave Challis <dave@suicas.net>
# Licensed under the GNU LGPL v2.1 - http://www.gnu.org/licenses/lgpl.html

"""Python wrapper for `Vowpal Wabbit's Latent Dirichlet Allocation <https://github.com/JohnLangford/vowpal_wabbit/>`_.

This uses `Matt Hoffman's online algorithm
<http://papers.nips.cc/paper/3902-online-learning-for-latent-dirichlet-allocation.pdf>`_, i.e. the same algorithm
that Gensim's :class:`~gensim.models.ldamodel.LdaModel` is based on.

Installation
------------
Use `official guide <https://github.com/JohnLangford/vowpal_wabbit>`_ or this one ::

    git clone https://github.com/JohnLangford/vowpal_wabbit.git
    cd vowpal_wabbit
    make
    make test
    sudo make install

Warnings
--------
Currently working and tested with Vowpal Wabbit versions 7.10 to 8.1.1. Vowpal Wabbit's API isn't currently stable,
so this may or may not work with older/newer versions. The aim will be to ensure this wrapper always works with
the latest release of Vowpal Wabbit.


Examples
--------

Train model

.. sourcecode:: pycon

    >>> from gensim.test.utils import common_corpus, common_dictionary
    >>> from gensim.models.wrappers import LdaVowpalWabbit
    >>>
    >>> path_to_wv_binary = "/path/to/vw/binary"
    >>> model = LdaVowpalWabbit(path_to_wv_binary, corpus=common_corpus, num_topics=20, id2word=common_dictionary)

Update existing model

.. sourcecode:: pycon

    >>> another_corpus = [[(1, 1), (2, 1)], [(3, 5)]]
    >>> model.update(another_corpus)

Get topic probability distributions for a document

.. sourcecode:: pycon

    >>> document_bow = [(1, 1)]
    >>> print(model[document_bow])

Print topics

.. sourcecode:: pycon

    >>> print(model.print_topics())

Save/load the trained model

.. sourcecode:: pycon

    >>> from gensim.test.utils import get_tmpfile
    >>>
    >>> temp_path = get_tmpfile("vw_lda.model")
    >>> model.save(temp_path)
    >>>
    >>> loaded_lda = LdaVowpalWabbit.load(temp_path)

Calculate log-perplexoty on given corpus

.. sourcecode:: pycon

    >>> another_corpus = [[(1, 1), (2, 1)], [(3, 5)]]
    >>> print(model.log_perpexity(another_corpus))

Vowpal Wabbit works on files, so this wrapper maintains a temporary directory while it's around,
reading/writing there as necessary.

"""
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import logging
import os
import shutil
import subprocess
import tempfile

import numpy

from gensim import utils, matutils
from gensim.models.ldamodel import LdaModel

logger = logging.getLogger(__name__)


class LdaVowpalWabbit(utils.SaveLoad):
    """Python wrapper using `Vowpal Wabbit's online LDA <https://github.com/JohnLangford/vowpal_wabbit/>`_.

    Communication between Vowpal Wabbit and Python takes place by passing around data files
    on disk and calling the 'vw' binary with the subprocess module.

    Warnings
    --------
    This is **only** python wrapper for `Vowpal Wabbit's online LDA <https://github.com/JohnLangford/vowpal_wabbit/>`_,
    you need to install original implementation first and pass the path to binary to ``vw_path``.

    """
    def __init__(self, vw_path, corpus=None, num_topics=100, id2word=None,
                 chunksize=256, passes=1, alpha=0.1, eta=0.1, decay=0.5,
                 offset=1, gamma_threshold=0.001, random_seed=None,
                 cleanup_files=True, tmp_prefix='tmp'):
        """

        Parameters
        ----------
        vw_path : str
            Path to Vowpal Wabbit's binary.
        corpus : iterable of list of (int, int), optional
            Collection of texts in BoW format. If given, training will start immediately,
            otherwise, you should call :meth:`~gensim.models.wrappers.ldavowpalwabbit.LdaVowpalWabbit.train` or
            :meth:`~gensim.models.wrappers.ldavowpalwabbit.LdaVowpalWabbit.update` manually for training.
        num_topics : int, optional
            Number of requested latent topics to be extracted from the training corpus.
            Corresponds to VW's ``--lda <num_topics>`` argument.
        id2word : :class:`~gensim.corpora.dictionary.Dictionary`, optional
            Mapping from word ids (integers) to words (strings).
        chunksize : int, optional
            Number of documents examined in each batch.
            Corresponds to VW's ``--minibatch <batch_size>`` argument.
        passes : int, optional
            Number of passes over the dataset to use.
            Corresponds to VW's ``--passes <passes>`` argument.
        alpha : float, optional
            Float effecting sparsity of per-document topic weights.
            This is applied symmetrically, and should be set higher to when documents are thought to look more similar.
            Corresponds to VW's ``--lda_alpha <alpha>`` argument.
        eta : float, optional
            Affects the sparsity of topic distributions.
            This is applied symmetrically, and should be set higher when topics
            are thought to look more similar.
            Corresponds to VW's ``--lda_rho <rho>`` argument.
        decay : float, optional
            Learning rate decay, affects how quickly learnt values are forgotten.
            Should be set to a value between 0.5 and 1.0 to guarantee convergence.
            Corresponds to VW's ``--power_t <tau>`` argument.
        offset: int, optional
            Learning offset, set to higher values to slow down learning on early iterations of the algorithm.
            Corresponds to VW's ``--initial_t <tau>`` argument.
        gamma_threshold : float, optional
            Affects when learning loop will be broken out of, higher values will result in earlier loop completion.
            Corresponds to VW's ``--epsilon <eps>`` argument.
        random_seed : int, optional
            Sets random seed when learning.
            Corresponds to VW's ``--random_seed <seed>`` argument.
        cleanup_files : bool, optional
            Whether or not to delete temporary directory and files used by this wrapper.
            Setting to False can be useful for debugging, or for re-using Vowpal Wabbit files elsewhere.
        tmp_prefix : str, optional
            To prefix temporary working directory name.

        """
        # default parameters are taken from Vowpal Wabbit's defaults, and
        # parameter names changed to match Gensim's LdaModel where possible
        self.vw_path = vw_path
        self.id2word = id2word

        if self.id2word is None:
            if corpus is None:
                raise ValueError(
                    "at least one of corpus/id2word must be specified, to establish input space dimensionality"
                )
            logger.warning("no word id mapping provided; initializing from corpus, assuming identity")
            self.id2word = utils.dict_from_corpus(corpus)
            self.num_terms = len(self.id2word)
        elif len(self.id2word) > 0:
            self.num_terms = 1 + max(self.id2word.keys())
        else:
            self.num_terms = 0

        if self.num_terms == 0:
            raise ValueError("cannot compute LDA over an empty collection (no terms)")

        # LDA parameters
        self.num_topics = num_topics
        self.chunksize = chunksize
        self.passes = passes
        self.alpha = alpha
        self.eta = eta
        self.gamma_threshold = gamma_threshold
        self.offset = offset
        self.decay = decay
        self.random_seed = random_seed
        self._initial_offset = offset

        # temporary files used for Vowpal Wabbit input/output
        self.tmp_dir = None
        self.tmp_prefix = tmp_prefix
        self.cleanup_files = cleanup_files
        self._init_temp_dir(tmp_prefix)

        # used for saving/loading this model's state
        self._model_data = None
        self._topics_data = None

        # cache loaded topics as numpy array
        self._topics = None

        if corpus is not None:
            self.train(corpus)

    def train(self, corpus):
        """Clear any existing model state, and train on given `corpus`.

        Parameters
        ----------
        corpus : iterable of list of (int, int)
            Collection of texts in BoW format.

        """
        logger.debug('Training new model from corpus')

        # reset any existing offset, model, or topics generated
        self.offset = self._initial_offset
        self._topics = None

        corpus_size = write_corpus_as_vw(corpus, self._corpus_filename)

        cmd = self._get_vw_train_command(corpus_size)

        _run_vw_command(cmd)

        # ensure that future updates of this model use correct offset
        self.offset += corpus_size

    def update(self, corpus):
        """Update existing model with `corpus`.

        Parameters
        ----------
        corpus : iterable of list of (int, int)
            Collection of texts in BoW format.

        """
        if not os.path.exists(self._model_filename):
            return self.train(corpus)

        logger.debug('Updating exiting model from corpus')

        # reset any existing topics generated
        self._topics = None

        corpus_size = write_corpus_as_vw(corpus, self._corpus_filename)

        cmd = self._get_vw_update_command(corpus_size)

        _run_vw_command(cmd)

        # ensure that future updates of this model use correct offset
        self.offset += corpus_size

    def log_perplexity(self, chunk):
        """Get per-word lower bound on log perplexity.

        Parameters
        ----------
        chunk : iterable of list of (int, int)
            Collection of texts in BoW format.

        Returns
        -------
        bound : float
            Per-word lower bound on log perplexity.

        """
        vw_data = self._predict(chunk)[1]
        corpus_words = sum(cnt for document in chunk for _, cnt in document)
        bound = -vw_data['average_loss']
        logger.info(
            "%.3f per-word bound, %.1f perplexity estimate based on a held-out corpus of %i documents with %i words",
            bound, numpy.exp2(-bound), vw_data['corpus_size'], corpus_words
        )
        return bound

    def get_topics(self):
        """Get topics X words matrix.

        Returns
        -------
        numpy.ndarray
            `num_topics` x `vocabulary_size` array of floats which represents the learned term topic matrix.

        """
        topics = self._get_topics()
        return topics / topics.sum(axis=1)[:, None]

    def print_topics(self, num_topics=10, num_words=10):
        """Alias for :meth:`~gensim.models.wrappers.dtmmodel.DtmModel.show_topics`.

        Parameters
        ----------
        num_topics : int, optional
            Number of topics to return, set `-1` to get all topics.
        num_words : int, optional
            Number of words.

        Returns
        -------
        list of str
            Topics as a list of strings

        """
        return self.show_topics(num_topics, num_words, log=True)

    def show_topics(self, num_topics=10, num_words=10, log=False, formatted=True):
        """Get the `num_words` most probable words for `num_topics` number of topics.

        Parameters
        ----------
        num_topics : int, optional
            Number of topics to return, set `-1` to get all topics.
        num_words : int, optional
            Number of words.
        log : bool, optional
            If True - will write topics with logger.
        formatted : bool, optional
            If `True` - return the topics as a list of strings, otherwise as lists of (weight, word) pairs.

        Returns
        -------
        list of str
            Topics as a list of strings (if formatted=True) **OR**
        list of (float, str)
            Topics as list of (weight, word) pairs (if formatted=False)

        """
        if num_topics < 0 or num_topics >= self.num_topics:
            num_topics = self.num_topics
        else:
            num_topics = min(num_topics, self.num_topics)

        chosen_topics = range(num_topics)
        shown = []

        for i in chosen_topics:
            if formatted:
                topic = self.print_topic(i, topn=num_words)
            else:
                topic = self.show_topic(i, topn=num_words)

            shown.append(topic)

            if log:
                logger.info("topic #%i (%.3f): %s", i, self.alpha, topic)

        return shown

    def print_topic(self, topicid, topn=10):
        """Get text representation of topic.

        Parameters
        ----------
        topicid : int
            Id of topic.
        topn : int, optional
            Top number of words in topic.

        Returns
        -------
        str
            Topic `topicid` in text representation.

        """
        return ' + '.join('{0:.3f}*{1}'.format(v[0], v[1]) for v in self.show_topic(topicid, topn))

    def show_topic(self, topicid, topn=10):
        """Get `num_words` most probable words for the given `topicid`.

        Parameters
        ----------
        topicid : int
            Id of topic.
        topn : int, optional
            Top number of topics that you'll receive.

        Returns
        -------
        list of (str, float)
            Sequence of probable words, as a list of `(word, word_probability)` for `topicid` topic.

        """
        topics = self._get_topics()
        topic = topics[topicid]
        bestn = matutils.argsort(topic, topn, reverse=True)
        return [(topic[t_id], self.id2word[t_id]) for t_id in bestn]

    def save(self, fname, *args, **kwargs):
        """Save model to file.

        Parameters
        ----------
        fname : str
            Path to output file.

        """
        if os.path.exists(self._model_filename):
            # Vowpal Wabbit uses its own binary model file, read this into
            # variable before serialising this object - keeps all data
            # self contained within a single serialised file
            logger.debug("Reading model bytes from '%s'", self._model_filename)
            with utils.open(self._model_filename, 'rb') as fhandle:
                self._model_data = fhandle.read()

        if os.path.exists(self._topics_filename):
            logger.debug("Reading topic bytes from '%s'", self._topics_filename)
            with utils.open(self._topics_filename, 'rb') as fhandle:
                self._topics_data = fhandle.read()

        if 'ignore' not in kwargs:
            kwargs['ignore'] = frozenset(['_topics', 'tmp_dir'])

        super(LdaVowpalWabbit, self).save(fname, *args, **kwargs)

    @classmethod
    def load(cls, fname, *args, **kwargs):
        """Load model from `fname`.

        Parameters
        ----------
        fname : str
            Path to file with :class:`~gensim.models.wrappers.ldavowpalwabbit.LdaVowpalWabbit`.

        """
        lda_vw = super(LdaVowpalWabbit, cls).load(fname, *args, **kwargs)
        lda_vw._init_temp_dir(prefix=lda_vw.tmp_prefix)

        if lda_vw._model_data:
            # Vowpal Wabbit operates on its own binary model file - deserialise
            # to file at load time, making it immediately ready for use
            logger.debug("Writing model bytes to '%s'", lda_vw._model_filename)
            with utils.open(lda_vw._model_filename, 'wb') as fhandle:
                fhandle.write(lda_vw._model_data)
            lda_vw._model_data = None  # no need to keep in memory after this

        if lda_vw._topics_data:
            logger.debug("Writing topic bytes to '%s'", lda_vw._topics_filename)
            with utils.open(lda_vw._topics_filename, 'wb') as fhandle:
                fhandle.write(lda_vw._topics_data)
            lda_vw._topics_data = None

        return lda_vw

    def __del__(self):
        """Cleanup the temporary directory used by this wrapper."""
        if self.cleanup_files and self.tmp_dir:
            logger.debug("Recursively deleting: %s", self.tmp_dir)
            shutil.rmtree(self.tmp_dir)

    def _init_temp_dir(self, prefix='tmp'):
        """Create a working temporary directory with given prefix.

        Parameters
        ----------
        prefix : str
            Prefix of the temporary directory.

        """
        self.tmp_dir = tempfile.mkdtemp(prefix=prefix)
        logger.info('using %s as temp dir', self.tmp_dir)

    def _get_vw_predict_command(self, corpus_size):
        """Get list of command line arguments for running prediction.

        Parameters
        ----------
        corpus_size : int
            Size of the corpus.

        """
        cmd = [
            self.vw_path,
            '--testonly',  # don't update model with this data
            '--lda_D', str(corpus_size),
            '-i', self._model_filename,  # load existing binary model
            '-d', self._corpus_filename,
            '--learning_rate', '0',  # possibly not needed, but harmless
            '-p', self._predict_filename
        ]

        if self.random_seed is not None:
            cmd.extend(['--random_seed', str(self.random_seed)])

        return cmd

    def _get_vw_train_command(self, corpus_size, update=False):
        """Get list of command line arguments for running model training.

        Parameters
        ----------
        corpus_size : int
            Size of corpus.
        update : bool
            Set `True` to further train an existing model.

        Returns
        -------
        list of str
            Sequence of all training parameters.

        """
        cmd = [
            self.vw_path,
            '-d', self._corpus_filename,
            '--power_t', str(self.decay),
            '--initial_t', str(self.offset),
            '--minibatch', str(self.chunksize),
            '--lda_D', str(corpus_size),
            '--passes', str(self.passes),
            '--cache_file', self._cache_filename,
            '--lda_epsilon', str(self.gamma_threshold),
            '--readable_model', self._topics_filename,
            '-k',  # clear cache
            '-f', self._model_filename
        ]

        if update:
            cmd.extend(['-i', self._model_filename])
        else:
            # these params are read from model file if updating
            cmd.extend([
                '--lda', str(self.num_topics),
                '-b', str(self.num_terms.bit_length()),
                '--lda_alpha', str(self.alpha),
                '--lda_rho', str(self.eta)
            ])

        if self.random_seed is not None:
            cmd.extend(['--random_seed', str(self.random_seed)])

        return cmd

    def _get_vw_update_command(self, corpus_size):
        """Get list of command line arguments to update a model.
        Alias for :meth:`~gensim.models.wrappers.dtmmodel.DtmModel._get_vw_train_command`

        Parameters
        ----------
        corpus_size : int
            Size of the corpus.

        Returns
        -------
        list of str
            Sequence of all training parameters.

        """
        return self._get_vw_train_command(corpus_size, update=True)

    def _load_vw_topics(self):
        """Read topics file generated by Vowpal Wabbit, convert to numpy array."""
        topics = numpy.zeros((self.num_topics, self.num_terms), dtype=numpy.float32)

        with utils.open(self._topics_filename, 'rb') as topics_file:
            found_data = False

            for line in topics_file:
                # look for start of data
                if not found_data:
                    if line.startswith(b'0 ') and b':' not in line:
                        found_data = True
                    else:
                        continue

                fields = line.split()
                word_id = int(fields[0])

                # output contains entries for 2**b terms, where b was set
                # by the '-b' option, ignore anything past num_terms
                if word_id >= self.num_terms:
                    break

                topics[:, word_id] = fields[1:]

        # normalise to probability distribution
        self._topics = topics / topics.sum(axis=1, keepdims=True)

    def _get_topics(self):
        """Get topics matrix, load from file if necessary."""
        if self._topics is None:
            self._load_vw_topics()
        return self._topics

    def _predict(self, chunk):
        """Run given chunk of documents against currently trained model.

        Parameters
        ----------
        chunk : iterable of list of (int, int)
            Sequence of documents in BoW format.

        Returns
        -------
        predictions : ndarray
            Tuple of prediction matrix.
        vw_data : dict
            Vowpal Wabbit data.

        """
        corpus_size = write_corpus_as_vw(chunk, self._corpus_filename)

        cmd = self._get_vw_predict_command(corpus_size)
        vw_data = _parse_vw_output(_run_vw_command(cmd))
        vw_data['corpus_size'] = corpus_size

        predictions = numpy.zeros((corpus_size, self.num_topics), dtype=numpy.float32)

        with utils.open(self._predict_filename, 'rb') as fhandle:
            for i, line in enumerate(fhandle):
                predictions[i, :] = line.split()

        predictions = predictions / predictions.sum(axis=1, keepdims=True)

        return predictions, vw_data

    def __getitem__(self, bow, eps=0.01):
        """Convert document or corpus in BoW format to LDA vectors in BoW format

        Parameters
        ----------
        bow : {list of (int, int), iterable of list of (int, int)}
            Document or corpus in BoW format.
        eps : float
            Threshold value (all topics with probability < `eps` will be ignored.

        Returns
        -------
        list of (int, float)
            LDA vector for document **OR**
        list of list of (int, float)
            LDA vectors for corpus.

        """
        is_corpus, dummy_corpus = utils.is_corpus(bow)
        if not is_corpus:
            bow = [bow]

        predictions = self._predict(bow)[0]

        topics = []
        for row in predictions:
            row_topics = []
            for topic_id, val in enumerate(row):
                if val > eps:
                    row_topics.append((topic_id, val))
            topics.append(row_topics)

        return topics if is_corpus else topics[0]

    def _get_filename(self, name):
        """Get path to given filename in temp directory.

        Parameters
        ----------
        name : str
            Name of the file.

        Returns
        -------
        str
            Path to a file.

        """
        return os.path.join(self.tmp_dir, name)

    @property
    def _model_filename(self):
        """Get path to file to write Vowpal Wabbit model to.

        Returns
        -------
        str
            Path to file to write Vowpal Wabbit model to.

        """
        return self._get_filename('model.vw')

    @property
    def _cache_filename(self):
        """Get path to file to write Vowpal Wabbit cache to.

        Returns
        -------
        str
            Path to file to write Vowpal Wabbit cache to.

        """
        return self._get_filename('cache.vw')

    @property
    def _corpus_filename(self):
        """Get path to file to write Vowpal Wabbit corpus to.

        Returns
        -------
        str
            Path to file to write Vowpal Wabbit corpus to.

        """
        return self._get_filename('corpus.vw')

    @property
    def _topics_filename(self):
        """Get path to file to write Vowpal Wabbit topics to.

        Returns
        -------
        str
            Path to file to write Vowpal Wabbit topics to.

        """
        return self._get_filename('topics.vw')

    @property
    def _predict_filename(self):
        """Get path to file to write Vowpal Wabbit predictions to.

        Returns
        -------
        str
            Path to file to write Vowpal Wabbit predictions to.

        """
        return self._get_filename('predict.vw')

    def __str__(self):
        """Get text representation of model."""
        fields = ['num_terms', 'num_topics', 'chunksize', 'alpha', 'eta']
        kv = ["{0}={1}".format(field, getattr(self, field)) for field in fields]
        return "{0}({1})".format(self.__class__.__name__, ', '.join(kv))


def corpus_to_vw(corpus):
    """Convert corpus to Vowpal Wabbit format.

    Parameters
    ----------
    corpus : iterable of list of (int, int)
        Collection of texts in BoW format.


    Notes
    -----

    Vowpal Wabbit format ::

        | 4:7 14:1 22:8 6:3
        | 14:22 22:4 0:1 1:3
        | 7:2 8:2


    Yields
    ------
    str
        Corpus in Vowpal Wabbit, line by line.

    """
    for entries in corpus:
        line = ['|']
        for word_id, count in entries:
            line.append("{0}:{1}".format(word_id, count))
        yield ' '.join(line)


def write_corpus_as_vw(corpus, filename):
    """Covert `corpus` to  Vowpal Wabbit format and save it to `filename`.

    Parameters
    ----------
    corpus : iterable of list of (int, int)
        Collection of texts in BoW format.
    filename : str
        Path to output file.

    Returns
    -------
    int
        Number of lines in `filename`.

    """
    logger.debug("Writing corpus to: %s", filename)

    corpus_size = 0
    with utils.open(filename, 'wb') as corpus_file:
        for line in corpus_to_vw(corpus):
            corpus_file.write(line.encode('utf-8') + b'\n')
            corpus_size += 1

    return corpus_size


def _parse_vw_output(text):
    """Get dict of useful fields from Vowpal Wabbit's output.

    Parameters
    ----------
    text : str
        Text from vw file.

    Returns
    -------
    dict of (str, float)
        Dictionary with field "average_loss", lower bound on mean per-word log-perplexity.

    """
    data = {}
    for line in text.splitlines():
        if line.startswith('average loss'):
            data['average_loss'] = float(line.split('=')[1])
            break

    return data


def _run_vw_command(cmd):
    """Execute given Vowpal Wabbit command, log stdout and stderr.

    Parameters
    ----------
    cmd : str
        Given Vowpal Wabbit command to execute.

    Returns
    -------
    str
        Stdout and stderr.

    Raises
    ------
    subprocess.CalledProcessError
        If something goes wrong.

    """
    logger.info("Running Vowpal Wabbit command: %s", ' '.join(cmd))
    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT)
    output = proc.communicate()[0].decode('utf-8')
    logger.debug("Vowpal Wabbit output: %s", output)

    if proc.returncode != 0:
        raise subprocess.CalledProcessError(proc.returncode, ' '.join(cmd), output=output)

    return output


def vwmodel2ldamodel(vw_model, iterations=50):
    """Convert :class:`~gensim.models.wrappers.ldavowpalwabbit.LdaVowpalWabbit` to
    :class:`~gensim.models.ldamodel.LdaModel`.

    This works by simply copying the training model weights (alpha, beta...) from a trained vwmodel
    into the gensim model.

    Parameters
    ----------
    vw_model : :class:`~gensim.models.wrappers.ldavowpalwabbit.LdaVowpalWabbit`
        Trained Vowpal Wabbit model.
    iterations : int
        Number of iterations to be used for inference of the new :class:`~gensim.models.ldamodel.LdaModel`.

    Returns
    -------
    :class:`~gensim.models.ldamodel.LdaModel`.
        Gensim native LDA.

    """
    model_gensim = LdaModel(
        num_topics=vw_model.num_topics, id2word=vw_model.id2word, chunksize=vw_model.chunksize,
        passes=vw_model.passes, alpha=vw_model.alpha, eta=vw_model.eta, decay=vw_model.decay,
        offset=vw_model.offset, iterations=iterations, gamma_threshold=vw_model.gamma_threshold,
        dtype=numpy.float32
    )
    model_gensim.expElogbeta[:] = vw_model._get_topics()
    return model_gensim
