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"""Comparing two saves of the same document. Date and time fields keep the value they had when the document was saved, so two
saves differ there by design; everything else in content.xml and styles.xml must be identical."""
import re
import zipfile

PARTS = ("content.xml", "styles.xml")
_FIELD = re.compile(r"(<text:(?:time|date)\b)([^>]*)>[^<]*(</text:(?:time|date)>)")
_VALUE = re.compile(r'\s+text:(?:time|date)-value="[^"]*"')


def normalize(xml):
    """`xml` with the cached text and the value attribute of text:date and text:time fields removed."""
    return _FIELD.sub(lambda m: m.group(1) + _VALUE.sub("", m.group(2)) + ">" + m.group(3), xml)


def differing_parts(first, second):
    """Names of the parts of two packages whose normalized content differs. A part that only one of them has differs; a part that
    neither has (a Base document has no styles.xml) is left out."""
    with zipfile.ZipFile(first) as a, zipfile.ZipFile(second) as b:
        have_a, have_b = set(a.namelist()), set(b.namelist())
        return [p for p in PARTS if (p in have_a or p in have_b) and
                (p not in have_a or p not in have_b or normalize(a.read(p).decode("utf-8")) != normalize(b.read(p).decode("utf-8")))]