chrislit/abydos

# Copyright 2014-2020 by Christopher C. Little.
# This file is part of Abydos.
#
# Abydos is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Abydos is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Abydos. If not, see <http://www.gnu.org/licenses/>.

"""abydos.compression._rle.

Run-Length Encoding encoder/decoder
"""

from itertools import groupby

__all__ = ['RLE']


class RLE:
    """Run-Length Encoding.

    Cf. :cite:`Robinson:1967`.

    Based on http://rosettacode.org/wiki/Run-length_encoding#Python
    :cite:`rosettacode:2018`. This is licensed GFDL 1.2.

    Digits 0-9 cannot be in text.

    .. versionadded:: 0.3.6
    """

    def encode(self, text: str) -> str:
        r"""Perform encoding of run-length-encoding (RLE).

        Parameters
        ----------
        text : str
            A text string to encode

        Returns
        -------
        str
            Word decoded by RLE

        Examples
        --------
        >>> from abydos.compression import BWT
        >>> rle = RLE()
        >>> bwt = BWT()
        >>> rle.encode(bwt.encode('align'))
        'n\x00ilag'
        >>> rle.encode('align')
        'align'

        >>> rle.encode(bwt.encode('banana'))
        'annb\x00aa'
        >>> rle.encode('banana')
        'banana'

        >>> rle.encode(bwt.encode('aaabaabababa'))
        'ab\x00abbab5a'
        >>> rle.encode('aaabaabababa')
        '3abaabababa'

        .. versionadded:: 0.1.0
        .. versionchanged:: 0.3.6
            Encapsulated in class

        """
        if text:
            text = ''.join(
                (str(n) + k if n > 2 else (k if n == 1 else 2 * k))
                for n, k in ((len(list(g)), k) for k, g in groupby(text))
            )
        return text

    def decode(self, text: str) -> str:
        r"""Perform decoding of run-length-encoding (RLE).

        Parameters
        ----------
        text : str
            A text string to decode

        Returns
        -------
        str
            Word decoded by RLE

        Examples
        --------
        >>> from abydos.compression import BWT
        >>> rle = RLE()
        >>> bwt = BWT()
        >>> bwt.decode(rle.decode('n\x00ilag'))
        'align'
        >>> rle.decode('align')
        'align'

        >>> bwt.decode(rle.decode('annb\x00aa'))
        'banana'
        >>> rle.decode('banana')
        'banana'

        >>> bwt.decode(rle.decode('ab\x00abbab5a'))
        'aaabaabababa'
        >>> rle.decode('3abaabababa')
        'aaabaabababa'

        .. versionadded:: 0.1.0
        .. versionchanged:: 0.3.6
            Encapsulated in class

        """
        mult = ''
        decoded = []
        for letter in list(text):
            if not letter.isdigit():
                if mult:
                    decoded.append(int(mult) * letter)
                    mult = ''
                else:
                    decoded.append(letter)
            else:
                mult += letter

        text = ''.join(decoded)
        return text


if __name__ == '__main__':
    import doctest

    doctest.testmod()