pdf2zh/pdfpage.py

import itertools
import logging
from typing import Any, BinaryIO, Container, Dict, Iterator, List, Optional, Set, Tuple

from pdf2zh import settings
from pdf2zh.pdfdocument import (
    PDFDocument,
    PDFNoPageLabels,
    PDFTextExtractionNotAllowed,
)
from pdf2zh.pdfexceptions import PDFObjectNotFound, PDFValueError
from pdf2zh.pdfparser import PDFParser
from pdf2zh.pdftypes import dict_value, int_value, list_value, resolve1
from pdf2zh.psparser import LIT
from pdf2zh.utils import parse_rect

log = logging.getLogger(__name__)

# some predefined literals and keywords.
LITERAL_PAGE = LIT("Page")
LITERAL_PAGES = LIT("Pages")


class PDFPage:
    """An object that holds the information about a page.

    A PDFPage object is merely a convenience class that has a set
    of keys and values, which describe the properties of a page
    and point to its contents.

    Attributes
    ----------
      doc: a PDFDocument object.
      pageid: any Python object that can uniquely identify the page.
      attrs: a dictionary of page attributes.
      contents: a list of PDFStream objects that represents the page content.
      lastmod: the last modified time of the page.
      resources: a dictionary of resources used by the page.
      mediabox: the physical size of the page.
      cropbox: the crop rectangle of the page.
      rotate: the page rotation (in degree).
      annots: the page annotations.
      beads: a chain that represents natural reading order.
      label: the page's label (typically, the logical page number).

    """

    def __init__(
        self,
        doc: PDFDocument,
        pageid: object,
        attrs: object,
        label: Optional[str],
    ) -> None:
        """Initialize a page object.

        doc: a PDFDocument object.
        pageid: any Python object that can uniquely identify the page.
        attrs: a dictionary of page attributes.
        label: page label string.
        """
        self.doc = doc
        self.pageid = pageid
        self.pageno = 0
        self.attrs = dict_value(attrs)
        self.label = label
        self.lastmod = resolve1(self.attrs.get("LastModified"))
        self.resources: Dict[object, object] = resolve1(
            self.attrs.get("Resources", dict()),
        )
        mediabox_params: List[Any] = [
            resolve1(mediabox_param) for mediabox_param in self.attrs["MediaBox"]
        ]
        self.mediabox = parse_rect(resolve1(mediabox_params))
        self.cropbox = self.mediabox
        if "CropBox" in self.attrs:
            try:
                self.cropbox = parse_rect(resolve1(self.attrs["CropBox"]))
            except PDFValueError:
                pass

        self.rotate = (int_value(self.attrs.get("Rotate", 0)) + 360) % 360
        self.annots = self.attrs.get("Annots")
        self.beads = self.attrs.get("B")
        if "Contents" in self.attrs:
            contents = resolve1(self.attrs["Contents"])
        else:
            contents = []
        if not isinstance(contents, list):
            contents = [contents]
        self.contents: List[object] = contents

    def __repr__(self) -> str:
        return f"<PDFPage: Resources={self.resources!r}, MediaBox={self.mediabox!r}>"

    INHERITABLE_ATTRS = {"Resources", "MediaBox", "CropBox", "Rotate"}

    @classmethod
    def create_pages(cls, document: PDFDocument) -> Iterator["PDFPage"]:
        def depth_first_search(
            obj: Any,
            parent: Dict[str, Any],
            visited: Optional[Set[Any]] = None,
        ) -> Iterator[Tuple[int, Dict[Any, Dict[Any, Any]]]]:
            if isinstance(obj, int):
                object_id = obj
                object_properties = dict_value(document.getobj(object_id)).copy()
            else:
                # This looks broken. obj.objid means obj could be either
                # PDFObjRef or PDFStream, but neither is valid for dict_value.
                object_id = obj.objid  # type: ignore[attr-defined]
                object_properties = dict_value(obj).copy()

            # Avoid recursion errors by keeping track of visited nodes
            if visited is None:
                visited = set()
            if object_id in visited:
                return
            visited.add(object_id)

            for k, v in parent.items():
                if k in cls.INHERITABLE_ATTRS and k not in object_properties:
                    object_properties[k] = v

            object_type = object_properties.get("Type")
            if object_type is None and not settings.STRICT:  # See #64
                object_type = object_properties.get("type")

            if object_type is LITERAL_PAGES and "Kids" in object_properties:
                # log.debug("Pages: Kids=%r", object_properties["Kids"])
                for child in list_value(object_properties["Kids"]):
                    yield from depth_first_search(child, object_properties, visited)

            elif object_type is LITERAL_PAGE:
                # log.debug("Page: %r", object_properties)
                yield (object_id, object_properties)

        try:
            page_labels: Iterator[Optional[str]] = document.get_page_labels()
        except PDFNoPageLabels:
            page_labels = itertools.repeat(None)

        pages = False
        if "Pages" in document.catalog:
            objects = depth_first_search(document.catalog["Pages"], document.catalog)
            for objid, tree in objects:
                yield cls(document, objid, tree, next(page_labels))
                pages = True
        if not pages:
            # fallback when /Pages is missing.
            for xref in document.xrefs:
                for objid in xref.get_objids():
                    try:
                        obj = document.getobj(objid)
                        if isinstance(obj, dict) and obj.get("Type") is LITERAL_PAGE:
                            yield cls(document, objid, obj, next(page_labels))
                    except PDFObjectNotFound:
                        pass

    @classmethod
    def get_pages(
        cls,
        fp: BinaryIO,
        pagenos: Optional[Container[int]] = None,
        maxpages: int = 0,
        password: str = "",
        caching: bool = True,
        check_extractable: bool = False,
    ) -> Iterator["PDFPage"]:
        # Create a PDF parser object associated with the file object.
        parser = PDFParser(fp)
        # Create a PDF document object that stores the document structure.
        doc = PDFDocument(parser, password=password, caching=caching)
        # Check if the document allows text extraction.
        # If not, warn the user and proceed.
        if not doc.is_extractable:
            if check_extractable:
                error_msg = "Text extraction is not allowed: %r" % fp
                raise PDFTextExtractionNotAllowed(error_msg)
            else:
                warning_msg = (
                    "The PDF %r contains a metadata field "
                    "indicating that it should not allow "
                    "text extraction. Ignoring this field "
                    "and proceeding. Use the check_extractable "
                    "if you want to raise an error in this case" % fp
                )
                log.warning(warning_msg)
        # Process each page contained in the document.
        for pageno, page in enumerate(cls.create_pages(doc)):
            page.pageno = pageno
            if pagenos and (pageno not in pagenos):
                continue
            yield page
            if maxpages and maxpages <= pageno + 1:
                break