#!/usr/bin/env python
"""
Segment a .po file to produce smaller files based on the locations of the
messages.
"""

import copy
import fnmatch
import logging
import sys
import argparse
import polib
import textwrap

from i18n.config import CONFIGURATION

LOG = logging.getLogger(__name__)


def segment_pofiles(locale):
    """Segment all the pofiles for `locale`.

    Returns a set of filenames, all the segment files written.

    """
    files_written = set()
    for filename, segments in CONFIGURATION.segment.items():
        filename = CONFIGURATION.get_messages_dir(locale) / filename
        files_written.update(segment_pofile(filename, segments))
    return files_written


def segment_pofile(filename, segments):
    """Segment a .po file using patterns in `segments`.

    The .po file at `filename` is read, and the occurrence locations of its
    messages are examined.  `segments` is a dictionary: the keys are segment
    .po filenames, the values are lists of patterns::

        {
            'django-studio.po': [
                'cms/*',
                'some-other-studio-place/*',
            ],
            'django-weird.po': [
                '*/weird_*.*',
            ],
        }

    If all a message's occurrences match the patterns for a segment, then that
    message is written to the new segmented .po file.

    Any message that matches no segments, or more than one, is written back to
    the original file.

    Arguments:
        filename (path.path): a path object referring to the original .po file.
        segments (dict): specification of the segments to create.

    Returns:
        a set of path objects, all the segment files written.

    """
    reading_msg = "Reading {num} entries from {file}"
    writing_msg = "Writing {num} entries to {file}"

    source_po = polib.pofile(filename)
    LOG.info(reading_msg.format(file=filename, num=len(source_po)))

    # A new pofile just like the source, but with no messages. We'll put
    # anything not segmented into this file.
    remaining_po = copy.deepcopy(source_po)
    remaining_po[:] = []

    # Turn the segments dictionary into two structures: segment_patterns is a
    # list of (pattern, segmentfile) pairs.  segment_po_files is a dict mapping
    # segment file names to pofile objects of their contents.
    segment_po_files = {filename: remaining_po}
    segment_patterns = []
    for segmentfile, patterns in segments.items():
        segment_po_files[segmentfile] = copy.deepcopy(remaining_po)
        segment_patterns.extend((pat, segmentfile) for pat in patterns)

    # Examine each message in the source file. If all of its occurrences match
    # a pattern for the same segment, it goes in that segment.  Otherwise, it
    # goes in remaining.
    for msg in source_po:
        msg_segments = set()
        for occ_file, _ in msg.occurrences:
            for pat, segment_file in segment_patterns:
                if fnmatch.fnmatch(occ_file, pat):
                    msg_segments.add(segment_file)
                    break
            else:
                msg_segments.add(filename)

        assert msg_segments
        if len(msg_segments) == 1:
            # This message belongs in this segment.
            segment_file = msg_segments.pop()
            segment_po_files[segment_file].append(msg)
        else:
            # It's in more than one segment, so put it back in the main file.
            remaining_po.append(msg)

    # Write out the results.
    files_written = set()
    for segment_file, pofile in segment_po_files.items():
        out_file = filename.dirname() / segment_file
        if len(pofile) == 0:
            LOG.error("No messages to write to {file}, did you run segment twice?".format(file=out_file))
        else:
            LOG.info(writing_msg.format(file=out_file, num=len(pofile)))
            pofile.save(out_file)
            files_written.add(out_file)

    return files_written


def main(locales=None, verbosity=1):  # pylint: disable=unused-argument
    """
    Main entry point of script
    """
    # This is used as a tool only to segment translation files when adding a
    # new segment.  In the regular workflow, the work is done by the extract
    # phase calling the functions above.
    locales = locales or []
    for locale in locales:
        segment_pofiles(locale)


if __name__ == "__main__":
    logging.basicConfig(stream=sys.stdout, level=logging.INFO)

    # pylint: disable=invalid-name
    description = textwrap.dedent("""
        Segment the .po files in LOCALE(s) based on the segmenting rules in
        config.yaml.

        Note that segmenting is *not* idempotent: it modifies the input file, so
        be careful that you don't run it twice on the same file.
    """.strip())

    parser = argparse.ArgumentParser(description=description)
    parser.add_argument("locale", nargs="+", help="a locale to segment")
    parser.add_argument("--verbose", "-v", action="count", default=0)
    args = parser.parse_args()
    main(locales=args.locale, verbosity=args.verbose)
