OCRmyPDF/src/ocrmypdf/pdfinfo/layout.py

# © 2018 James R. Barlow: github.com/jbarlow83
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.


import re
from math import copysign
from pathlib import Path
from unittest.mock import patch

import pdfminer
import pdfminer.encodingdb
import pdfminer.pdfdevice
import pdfminer.pdfinterp
from pdfminer.converter import PDFLayoutAnalyzer
from pdfminer.layout import LAParams, LTChar, LTPage, LTTextBox
from pdfminer.pdfdocument import PDFTextExtractionNotAllowed
from pdfminer.pdffont import PDFSimpleFont, PDFUnicodeNotDefined
from pdfminer.pdfpage import PDFPage
from pdfminer.utils import bbox2str, matrix2str

from ocrmypdf.exceptions import EncryptedPdfError, InputFileError

STRIP_NAME = re.compile(r'[0-9]+')


original_PDFSimpleFont_init = PDFSimpleFont.__init__


def PDFSimpleFont__init__(self, descriptor, widths, spec):
    # Font encoding is specified either by a name of
    # built-in encoding or a dictionary that describes
    # the differences.
    original_PDFSimpleFont_init(self, descriptor, widths, spec)
    # pdfminer is incorrect. If there is no ToUnicode and no Encoding, do not
    # assume Unicode conversion is possible. RM 9.10.2
    if not self.unicode_map and 'Encoding' not in spec:
        self.cid2unicode = {}
    return


PDFSimpleFont.__init__ = PDFSimpleFont__init__

#
# pdfminer patches when creator is PScript5.dll
#


def PDFType3Font__PScript5_get_height(self):
    h = self.bbox[3] - self.bbox[1]
    if h == 0:
        h = self.ascent - self.descent
    return h * copysign(1.0, self.vscale)


def PDFType3Font__PScript5_get_descent(self):
    return self.descent * copysign(1.0, self.vscale)


def PDFType3Font__PScript5_get_ascent(self):
    return self.ascent * copysign(1.0, self.vscale)


class LTStateAwareChar(LTChar):
    """A subclass of LTChar that tracks text render mode at time of drawing"""

    __slots__ = (
        'rendermode',
        '_text',
        'matrix',
        'fontname',
        'adv',
        'upright',
        'size',
        'width',
        'height',
        'bbox',
        'x0',
        'x1',
        'y0',
        'y1',
    )

    def __init__(
        self,
        matrix,
        font,
        fontsize,
        scaling,
        rise,
        text,
        textwidth,
        textdisp,
        ncs,
        graphicstate,
        textstate,
    ):
        super().__init__(
            matrix,
            font,
            fontsize,
            scaling,
            rise,
            text,
            textwidth,
            textdisp,
            ncs,
            graphicstate,
        )
        self.rendermode = textstate.render

    def is_compatible(self, obj):
        """Check if characters can be combined into a textline

        We consider characters compatible if:
            - the Unicode mapping is known, and both have the same render mode
            - the Unicode mapping is unknown but both are part of the same font
        """
        # pylint: disable=protected-access
        both_unicode_mapped = isinstance(self._text, str) and isinstance(obj._text, str)
        try:
            if both_unicode_mapped:
                return self.rendermode == obj.rendermode
            font0, _ = self._text
            font1, _ = obj._text
            return font0 == font1 and self.rendermode == obj.rendermode
        except (ValueError, AttributeError):
            return False

    def get_text(self):
        if isinstance(self._text, tuple):
            return '\ufffd'  # standard 'Unknown symbol'
        return self._text

    def __repr__(self):
        return '<{} {} matrix={} rendermode={!r} font={!r} adv={} text={!r}>'.format(
            self.__class__.__name__,
            bbox2str(self.bbox),
            matrix2str(self.matrix),
            self.rendermode,
            self.fontname,
            self.adv,
            self.get_text(),
        )


class TextPositionTracker(PDFLayoutAnalyzer):
    """A page layout analyzer that pays attention to text visibility"""

    def __init__(self, rsrcmgr, pageno=1, laparams=None):
        super().__init__(rsrcmgr, pageno, laparams)
        self.textstate = None
        self.result = None
        self.cur_item = None  # not defined in pdfminer code as it should be

    def begin_page(self, page, ctm):
        super().begin_page(page, ctm)
        self.cur_item = LTPage(self.pageno, page.mediabox)

    def end_page(self, page):
        assert not self._stack, str(len(self._stack))
        assert isinstance(self.cur_item, LTPage), str(type(self.cur_item))
        if self.laparams is not None:
            self.cur_item.analyze(self.laparams)
        self.pageno += 1
        self.receive_layout(self.cur_item)

    def render_string(self, textstate, seq, ncs, graphicstate):
        self.textstate = textstate.copy()
        super().render_string(self.textstate, seq, ncs, graphicstate)

    def render_char(
        self, matrix, font, fontsize, scaling, rise, cid, ncs, graphicstate
    ):
        try:
            text = font.to_unichr(cid)
            assert isinstance(text, str), str(type(text))
        except PDFUnicodeNotDefined:
            text = self.handle_undefined_char(font, cid)
        textwidth = font.char_width(cid)
        textdisp = font.char_disp(cid)
        item = LTStateAwareChar(
            matrix,
            font,
            fontsize,
            scaling,
            rise,
            text,
            textwidth,
            textdisp,
            ncs,
            graphicstate,
            self.textstate,
        )
        self.cur_item.add(item)
        return item.adv

    def handle_undefined_char(self, font, cid):
        # log.info('undefined: %r, %r', font, cid)
        return (font.fontname, cid)

    def receive_layout(self, ltpage):
        self.result = ltpage

    def get_result(self):
        return self.result


def get_page_analysis(infile, pageno, pscript5_mode):
    rman = pdfminer.pdfinterp.PDFResourceManager(caching=True)
    if pdfminer.__version__ < '20200402':
        # Workaround for https://github.com/pdfminer/pdfminer.six/issues/395
        disable_boxes_flow = 2
    else:
        disable_boxes_flow = None
    dev = TextPositionTracker(
        rman,
        laparams=LAParams(
            all_texts=True, detect_vertical=True, boxes_flow=disable_boxes_flow
        ),
    )
    interp = pdfminer.pdfinterp.PDFPageInterpreter(rman, dev)

    patcher = None
    if pscript5_mode:
        patcher = patch.multiple(
            'pdfminer.pdffont.PDFType3Font',
            spec=True,
            get_ascent=PDFType3Font__PScript5_get_ascent,
            get_descent=PDFType3Font__PScript5_get_descent,
            get_height=PDFType3Font__PScript5_get_height,
        )
        patcher.start()

    try:
        with Path(infile).open('rb') as f:
            page_iter = PDFPage.get_pages(f, pagenos=[pageno], maxpages=0)
            page = next(page_iter, None)
            if page is None:
                raise InputFileError(
                    f"pdfminer could not process page {pageno} (counting from 0)."
                )
            interp.process_page(page)
    except PDFTextExtractionNotAllowed as e:
        raise EncryptedPdfError() from e
    finally:
        if patcher is not None:
            patcher.stop()

    return dev.get_result()


def get_text_boxes(obj):
    for child in obj:
        if isinstance(child, (LTTextBox)):
            yield child
        else:
            try:
                yield from get_text_boxes(child)
            except TypeError:
                continue