339 lines
11 KiB
Python
339 lines
11 KiB
Python
"""
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Page labels are shown by PDF viewers as "the page number".
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A page has a numeric index, starting at 0. Additionally, the page
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has a label. In the most simple case:
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label = index + 1
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However, the title page and the table of contents might have Roman numerals as
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page labels. This makes things more complicated.
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Example 1
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---------
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>>> reader.root_object["/PageLabels"]["/Nums"]
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[0, IndirectObject(18, 0, 139929798197504),
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8, IndirectObject(19, 0, 139929798197504)]
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>>> reader.get_object(reader.root_object["/PageLabels"]["/Nums"][1])
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{'/S': '/r'}
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>>> reader.get_object(reader.root_object["/PageLabels"]["/Nums"][3])
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{'/S': '/D'}
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Example 2
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---------
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The following is a document with pages labeled
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i, ii, iii, iv, 1, 2, 3, A-8, A-9, ...
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1 0 obj
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<< /Type /Catalog
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/PageLabels << /Nums [
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0 << /S /r >>
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4 << /S /D >>
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7 << /S /D
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/P ( A- )
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/St 8
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>>
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% A number tree containing
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% three page label dictionaries
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]
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>>
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...
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>>
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endobj
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§12.4.2 PDF Specification 1.7 and 2.0
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=====================================
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Entries in a page label dictionary
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----------------------------------
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The /S key:
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D Decimal Arabic numerals
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R Uppercase Roman numerals
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r Lowercase Roman numerals
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A Uppercase letters (A to Z for the first 26 pages,
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AA to ZZ for the next 26, and so on)
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a Lowercase letters (a to z for the first 26 pages,
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aa to zz for the next 26, and so on)
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"""
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import string
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from typing import TYPE_CHECKING, Optional, cast
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from ._protocols import PdfCommonDocProtocol
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from ._utils import logger_warning
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from .generic import (
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ArrayObject,
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DictionaryObject,
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NullObject,
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NumberObject,
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is_null_or_none,
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)
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if TYPE_CHECKING:
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from collections.abc import Callable
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# The largest number one can represent using the usual symbols
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# and subtractive notation without additional conventions.
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# Aligns with https://github.com/AA-Turner/roman-numerals/blob/master/python/roman_numerals/__init__.py
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MAXIMUM_ROMAN_NUMERAL = 3_999
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# Allow values of up to 512 * 26 = 13_312 for the `/A` and `/a`.
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# Please note that this limit is somehow arbitrary and some trade-off
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# between rather restrictive <= 256 output bytes per label and the possibly
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# unrealistic 1000 output bytes per label.
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MAXIMUM_PAGE_LABEL_LENGTH = 512
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def number2uppercase_roman_numeral(num: int) -> str:
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if num <= 0:
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raise ValueError("Expecting a positive number.")
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if num > MAXIMUM_ROMAN_NUMERAL:
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raise ValueError("Number is out of range.")
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roman = [
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(1000, "M"),
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(900, "CM"),
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(500, "D"),
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(400, "CD"),
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(100, "C"),
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(90, "XC"),
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(50, "L"),
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(40, "XL"),
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(10, "X"),
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(9, "IX"),
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(5, "V"),
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(4, "IV"),
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(1, "I"),
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]
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result = []
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for value, symbol in roman:
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count, num = divmod(num, value)
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result.append(symbol * count)
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return "".join(result)
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def number2lowercase_roman_numeral(number: int) -> str:
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return number2uppercase_roman_numeral(number).lower()
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def number2uppercase_letter(number: int) -> str:
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if number <= 0:
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raise ValueError("Expecting a positive number.")
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# A to Z, then the same letter repeated: AA to ZZ, AAA to ZZZ, and so on.
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repetitions, position = divmod(number - 1, 26)
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length = repetitions + 1
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if length > MAXIMUM_PAGE_LABEL_LENGTH:
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raise ValueError("Number is too large.")
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return string.ascii_uppercase[position] * (repetitions + 1)
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def number2lowercase_letter(number: int) -> str:
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return number2uppercase_letter(number).lower()
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def get_label_from_nums(dictionary_object: DictionaryObject, index: int) -> str:
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# [Nums] shall be an array of the form
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# [ key_1 value_1 key_2 value_2 ... key_n value_n ]
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# where each key_i is an integer and the corresponding
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# value_i shall be the object associated with that key.
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# The keys shall be sorted in numerical order,
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# analogously to the arrangement of keys in a name tree
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# as described in 7.9.6, "Name Trees."
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nums = cast(ArrayObject, dictionary_object["/Nums"])
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nums_length = len(nums)
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i = 0
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value = None
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start_index = 0
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while i < nums_length:
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if i + 1 >= nums_length:
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logger_warning(
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"Ignoring last /Nums key without a value.", source=__name__
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)
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break
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start_index = nums[i]
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value = nums[i + 1].get_object()
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if i + 2 == nums_length:
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break
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if nums[i + 2] > index:
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break
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i += 2
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m: dict[Optional[str], Callable[[int], str]] = {
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None: lambda _: "",
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"/D": str,
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"/R": number2uppercase_roman_numeral,
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"/r": number2lowercase_roman_numeral,
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"/A": number2uppercase_letter,
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"/a": number2lowercase_letter,
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}
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# if /Nums array is not following the specification or if /Nums is empty
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if not isinstance(value, dict):
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return str(index + 1) # Fallback
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start = value.get("/St", 1)
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prefix = cast(str, value.get("/P", ""))
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mapping_function = m.get(value.get("/S"))
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if mapping_function is None:
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# Unknown /S numbering style; fall back to the page position.
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logger_warning(
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"Ignoring unknown page label numbering style %(style)r in /Nums.",
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source=__name__,
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style=value.get("/S"),
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)
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return str(index + 1) # Fallback
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try:
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return prefix + mapping_function(index - start_index + start)
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except (TypeError, ValueError) as exception:
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# Malformed /St or /P value; fall back to the page position.
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logger_warning(
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"Ignoring malformed page label entry in /Nums (/St=%(start)r, /P=%(prefix)r): %(exception)s",
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source=__name__,
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start=start,
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prefix=prefix,
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exception=exception,
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)
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return str(index + 1) # Fallback
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def index2label(reader: PdfCommonDocProtocol, index: int) -> str:
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"""
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See 7.9.7 "Number Trees".
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Args:
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reader: The PdfReader
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index: The index of the page
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Returns:
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The label of the page, e.g. "iv" or "4".
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"""
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root = cast(DictionaryObject, reader.root_object)
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if "/PageLabels" not in root:
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return str(index + 1) # Fallback
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number_tree = root["/PageLabels"].get_object()
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if not isinstance(number_tree, DictionaryObject):
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logger_warning(
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"Page labels are not a dictionary: %(number_tree)s",
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source=__name__,
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number_tree=number_tree,
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)
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return str(index + 1) # Fallback
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if "/Nums" in number_tree:
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return get_label_from_nums(number_tree, index)
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if "/Kids" in number_tree and not isinstance(number_tree["/Kids"], NullObject):
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# number_tree = {'/Kids': [IndirectObject(7333, 0, 140132998195856), ...]}
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# Limit maximum depth.
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level = 0
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while level < 100:
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kids = cast(list[DictionaryObject], number_tree["/Kids"])
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for kid in kids:
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# kid = {'/Limits': [0, 63], '/Nums': [0, {'/P': 'C1'}, ...]}
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limits = kid.get("/Limits", NullObject()).get_object()
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if not isinstance(limits, list) or len(limits) < 2:
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# Skip kids whose /Limits range is missing or malformed.
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logger_warning(
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"Ignoring kid with missing or malformed /Limits in /PageLabels.",
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source=__name__,
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)
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continue
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if limits[0] <= index <= limits[1]:
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if not is_null_or_none(kid.get("/Kids", None)):
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# Recursive definition.
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level += 1
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if level == 100: # pragma: no cover
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raise NotImplementedError(
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"Too deep nesting is not supported."
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)
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number_tree = kid
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# Exit the inner `for` loop and continue at the next level with the
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# next iteration of the `while` loop.
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break
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return get_label_from_nums(kid, index)
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else:
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# When there are no kids, make sure to exit the `while` loop directly
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# and continue with the fallback.
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break
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logger_warning("Could not reliably determine page label for %(index)d.", source=__name__, index=index)
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return str(index + 1) # Fallback if neither /Nums nor /Kids is in the number_tree
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def nums_insert(
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key: NumberObject,
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value: DictionaryObject,
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nums: ArrayObject,
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) -> None:
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"""
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Insert a key, value pair in a Nums array.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry
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value: value of the entry
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nums: Nums array to modify
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"""
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if len(nums) % 2 != 0:
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raise ValueError("A nums like array must have an even number of elements")
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i = len(nums)
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while i != 0 and key <= nums[i - 2]:
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i = i - 2
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if i < len(nums) and key == nums[i]:
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nums[i + 1] = value
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else:
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nums.insert(i, key)
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nums.insert(i + 1, value)
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def nums_clear_range(
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key: NumberObject,
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page_index_to: int,
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nums: ArrayObject,
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) -> None:
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"""
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Remove all entries in a number tree in a range after an entry.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry before the range
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page_index_to: The page index of the upper limit of the range
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nums: Nums array to modify
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"""
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if len(nums) % 2 != 0:
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raise ValueError("A nums like array must have an even number of elements")
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if page_index_to < key:
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raise ValueError("page_index_to must be greater or equal than key")
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i = nums.index(key) + 2
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while i < len(nums) and nums[i] <= page_index_to:
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nums.pop(i)
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nums.pop(i)
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def nums_next(
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key: NumberObject,
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nums: ArrayObject,
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) -> tuple[Optional[NumberObject], Optional[DictionaryObject]]:
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"""
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Return the (key, value) pair of the entry after the given one.
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See 7.9.7 "Number Trees".
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Args:
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key: number key of the entry
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nums: Nums array
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"""
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if len(nums) % 2 != 0:
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raise ValueError("A nums like array must have an even number of elements")
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i = nums.index(key) + 2
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if i < len(nums):
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return nums[i], nums[i + 1]
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return None, None
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