Mini Shell

"""Filename matching with shell patterns.

fnmatch(FILENAME, PATTERN) matches according to the local convention.
fnmatchcase(FILENAME, PATTERN) always takes case in account.

The functions operate by translating the pattern into a regular
expression.  They cache the compiled regular expressions for speed.

The function translate(PATTERN) returns a regular expression
corresponding to PATTERN.  (It does not compile it.)
"""
import os
import posixpath
import re
import functools

__all__ = ["filter", "fnmatch", "fnmatchcase", "translate"]

# Build a thread-safe incrementing counter to help create unique regexp group
# names across calls.
from itertools import count
_nextgroupnum = count().__next__
del count

def fnmatch(name, pat):
    """Test whether FILENAME matches PATTERN.

    Patterns are Unix shell style:

    *       matches everything
    ?       matches any single character
    [seq]   matches any character in seq
    [!seq]  matches any char not in seq

    An initial period in FILENAME is not special.
    Both FILENAME and PATTERN are first case-normalized
    if the operating system requires it.
    If you don't want this, use fnmatchcase(FILENAME, PATTERN).
    """
    name = os.path.normcase(name)
    pat = os.path.normcase(pat)
    return fnmatchcase(name, pat)

@functools.lru_cache(maxsize=256, typed=True)
def _compile_pattern(pat):
    if isinstance(pat, bytes):
        pat_str = str(pat, 'ISO-8859-1')
        res_str = translate(pat_str)
        res = bytes(res_str, 'ISO-8859-1')
    else:
        res = translate(pat)
    return re.compile(res).match

def filter(names, pat):
    """Construct a list from those elements of the iterable NAMES that match PAT."""
    result = []
    pat = os.path.normcase(pat)
    match = _compile_pattern(pat)
    if os.path is posixpath:
        # normcase on posix is NOP. Optimize it away from the loop.
        for name in names:
            if match(name):
                result.append(name)
    else:
        for name in names:
            if match(os.path.normcase(name)):
                result.append(name)
    return result

def fnmatchcase(name, pat):
    """Test whether FILENAME matches PATTERN, including case.

    This is a version of fnmatch() which doesn't case-normalize
    its arguments.
    """
    match = _compile_pattern(pat)
    return match(name) is not None


def translate(pat):
    """Translate a shell PATTERN to a regular expression.

    There is no way to quote meta-characters.
    """

    STAR = object()
    res = []
    add = res.append
    i, n = 0, len(pat)
    while i < n:
        c = pat[i]
        i = i+1
        if c == '*':
            # compress consecutive `*` into one
            if (not res) or res[-1] is not STAR:
                add(STAR)
        elif c == '?':
            add('.')
        elif c == '[':
            j = i
            if j < n and pat[j] == '!':
                j = j+1
            if j < n and pat[j] == ']':
                j = j+1
            while j < n and pat[j] != ']':
                j = j+1
            if j >= n:
                add('\\[')
            else:
                stuff = pat[i:j]
                if '--' not in stuff:
                    stuff = stuff.replace('\\', r'\\')
                else:
                    chunks = []
                    k = i+2 if pat[i] == '!' else i+1
                    while True:
                        k = pat.find('-', k, j)
                        if k < 0:
                            break
                        chunks.append(pat[i:k])
                        i = k+1
                        k = k+3
                    chunks.append(pat[i:j])
                    # Escape backslashes and hyphens for set difference (--).
                    # Hyphens that create ranges shouldn't be escaped.
                    stuff = '-'.join(s.replace('\\', r'\\').replace('-', r'\-')
                                     for s in chunks)
                # Escape set operations (&&, ~~ and ||).
                stuff = re.sub(r'([&~|])', r'\\\1', stuff)
                i = j+1
                if stuff[0] == '!':
                    stuff = '^' + stuff[1:]
                elif stuff[0] in ('^', '['):
                    stuff = '\\' + stuff
                add(f'[{stuff}]')
        else:
            add(re.escape(c))
    assert i == n

    # Deal with STARs.
    inp = res
    res = []
    add = res.append
    i, n = 0, len(inp)
    # Fixed pieces at the start?
    while i < n and inp[i] is not STAR:
        add(inp[i])
        i += 1
    # Now deal with STAR fixed STAR fixed ...
    # For an interior `STAR fixed` pairing, we want to do a minimal
    # .*? match followed by `fixed`, with no possibility of backtracking.
    # We can't spell that directly, but can trick it into working by matching
    #    .*?fixed
    # in a lookahead assertion, save the matched part in a group, then
    # consume that group via a backreference. If the overall match fails,
    # the lookahead assertion won't try alternatives. So the translation is:
    #     (?=(?P<name>.*?fixed))(?P=name)
    # Group names are created as needed: g0, g1, g2, ...
    # The numbers are obtained from _nextgroupnum() to ensure they're unique
    # across calls and across threads. This is because people rely on the
    # undocumented ability to join multiple translate() results together via
    # "|" to build large regexps matching "one of many" shell patterns.
    while i < n:
        assert inp[i] is STAR
        i += 1
        if i == n:
            add(".*")
            break
        assert inp[i] is not STAR
        fixed = []
        while i < n and inp[i] is not STAR:
            fixed.append(inp[i])
            i += 1
        fixed = "".join(fixed)
        if i == n:
            add(".*")
            add(fixed)
        else:
            groupnum = _nextgroupnum()
            add(f"(?=(?P<g{groupnum}>.*?{fixed}))(?P=g{groupnum})")
    assert i == n
    res = "".join(res)
    return fr'(?s:{res})\Z'