dinglehopper/qurator/dinglehopper/ocr_files.py

from __future__ import division, print_function

from typing import Optional
from warnings import warn

from lxml import etree as ET
from lxml.etree import XMLSyntaxError
from contextlib import suppress
from itertools import repeat
from .substitute_equivalences import substitute_equivalences
import sys
import attr
import enum
import unicodedata
import re


@attr.s(frozen=True)
class ExtractedText:
    segments = attr.ib(converter=list)
    joiner = attr.ib(type=str)
    # TODO Types are not validated (attr does not do this yet)

    @property
    def text(self):
        return self.joiner.join(s.text for s in self.segments)

    _segment_id_for_pos = None

    def segment_id_for_pos(self, pos):
        # Calculate segment ids once, on the first call
        if not self._segment_id_for_pos:
            segment_id_for_pos = []
            for s in self.segments:
                segment_id_for_pos.extend(repeat(s.segment_id, len(s.text)))
                segment_id_for_pos.extend(repeat(None, len(self.joiner)))
            # This is frozen, so we have to jump through the hoop:
            object.__setattr__(self, '_segment_id_for_pos', segment_id_for_pos)
            assert self._segment_id_for_pos

        return self._segment_id_for_pos[pos]


class Normalization(enum.Enum):
    NFC = 1
    NFC_MUFI = 2  # TODO
    NFC_SBB = 3


def normalize(text, normalization):
    if normalization == Normalization.NFC:
        return unicodedata.normalize('NFC', text)
    if normalization == Normalization.NFC_MUFI:
        raise NotImplementedError()
    if normalization == Normalization.NFC_SBB:
        return substitute_equivalences(text)
    else:
        raise ValueError()


# XXX hack
def normalize_sbb(t):
    return normalize(t, Normalization.NFC_SBB)


@attr.s(frozen=True)
class ExtractedTextSegment:
    segment_id = attr.ib(type=Optional[str])

    @segment_id.validator
    def check(self, _, value):
        if value is None:
            return
        if not re.match(r'[\w\d_-]+', value):
            raise ValueError('Malformed segment id "{}"'.format(value))
    text = attr.ib(type=str)

    @text.validator
    def check(self, _, value):
        if value is not None and normalize(value, self.normalization) != value:
            raise ValueError('String "{}" is not normalized.'.format(value))
    normalization = attr.ib(converter=Normalization, default=Normalization.NFC_SBB)

    @classmethod
    def from_text_segment(cls, text_segment, nsmap):
        """Build an ExtractedTextSegment from a PAGE content text element"""

        segment_id = text_segment.attrib['id']
        segment_text = None
        with suppress(AttributeError):
            segment_text = text_segment.find('./page:TextEquiv/page:Unicode', namespaces=nsmap).text
            segment_text = segment_text or ''
            segment_text = normalize_sbb(segment_text)
        return cls(segment_id, segment_text)


def alto_namespace(tree):
    """Return the ALTO namespace used in the given ElementTree.

    This relies on the assumption that, in any given ALTO file, the root element has the local name "alto". We do not
    check if the files uses any valid ALTO namespace.
    """
    root_name = ET.QName(tree.getroot().tag)
    if root_name.localname == 'alto':
        return root_name.namespace
    else:
        raise ValueError('Not an ALTO tree')


def alto_extract(tree):
    """Extract text from the given ALTO ElementTree."""

    nsmap = {'alto': alto_namespace(tree)}

    lines = (
        ' '.join(string.attrib.get('CONTENT') for string in line.iterfind('alto:String', namespaces=nsmap))
        for line in tree.iterfind('.//alto:TextLine', namespaces=nsmap))

    return ExtractedText(
            (ExtractedTextSegment(None, normalize_sbb(line_text)) for line_text in lines),
            '\n'
    )
    # TODO This currently does not extract any segment id, because we are
    #      clueless about the ALTO format.
    # FIXME needs to handle normalization


def alto_text(tree):
    return alto_extract(tree).text


def page_namespace(tree):
    """Return the PAGE content namespace used in the given ElementTree.

    This relies on the assumption that, in any given PAGE content file, the root element has the local name "PcGts". We
    do not check if the files uses any valid PAGE namespace.
    """
    root_name = ET.QName(tree.getroot().tag)
    if root_name.localname == 'PcGts':
        return root_name.namespace
    else:
        raise ValueError('Not a PAGE tree')


def page_extract(tree):
    """Extract text from the given PAGE content ElementTree."""

    nsmap = {'page': page_namespace(tree)}

    regions = []
    reading_order = tree.find('.//page:ReadingOrder', namespaces=nsmap)
    if reading_order is not None:
        for group in reading_order.iterfind('./*', namespaces=nsmap):
            if ET.QName(group.tag).localname == 'OrderedGroup':
                region_ref_indexeds = group.findall('./page:RegionRefIndexed', namespaces=nsmap)
                for region_ref_indexed in sorted(region_ref_indexeds, key=lambda r: int(r.attrib['index'])):
                    region_id = region_ref_indexed.attrib['regionRef']
                    region = tree.find('.//page:TextRegion[@id="%s"]' % region_id, namespaces=nsmap)
                    if region is not None:
                        regions.append(ExtractedTextSegment.from_text_segment(region, nsmap))
                    else:
                        warn('Not a TextRegion: "%s"' % region_id)
            else:
                raise NotImplementedError
    else:
        for region in tree.iterfind('.//page:TextRegion', namespaces=nsmap):
            regions.append(ExtractedTextSegment.from_text_segment(region, nsmap))

    # Filter empty region texts
    regions = (r for r in regions if r.text is not None)

    return ExtractedText(regions, '\n')
    # FIXME needs to handle normalization


def page_text(tree):
    return page_extract(tree).text


def plain_extract(filename):
    with open(filename, 'r') as f:
        return ExtractedText(
                (ExtractedTextSegment('line %d' % no, line) for no, line in enumerate(f.readlines())),
                '\n'
        )


def plain_text(filename):
    return plain_extract(filename).text


def extract(filename):
    """Extract the text from the given file.

    Supports PAGE, ALTO and falls back to plain text.
    """
    try:
        tree = ET.parse(filename)
    except XMLSyntaxError:
        return plain_extract(filename)
    try:
        return page_extract(tree)
    except ValueError:
        return alto_extract(tree)


def text(filename):
    return extract(filename).text


if __name__ == '__main__':
    print(text(sys.argv[1]))