def download_file(url, dest=None, chunk_size=1024, replace="ask",
                  label="Downloading {dest_basename} ({size:.2f}MB)",
                  expected_extension=None):
    """Download a file from a given URL and display progress.

    :param dest: If the destination exists and is a directory, the filename
        will be guessed from the Content-Disposition header. If the destination
        is an existing file, the user will either be prompted to overwrite, or
        the file will be replaced (depending on the value of **replace**). If
        the destination does not exist, it will be used as the filename.
    :param int chunk_size: bytes read in at a time.
    :param replace: If `False`, an existing destination file will not be
        overwritten.
    :param label: a string which is formatted and displayed as the progress bar
        label. Variables provided include *dest_basename*, *dest*, and *size*.
    :param expected_extension: if set, the filename will be sanitized to ensure
        it has the given extension. The extension should not start with a dot
        (`.`).
    """
    dest = Path(dest or url.split("/")[-1])
    response = get(url, stream=True)
    if (dest.exists()
            and dest.is_dir()
            and "Content-Disposition" in response.headers):
        content_disposition = rfc6266.parse_requests_response(response)
        if expected_extension is not None:
            filename = content_disposition.filename_sanitized(
                expected_extension)
        filename = secure_filename(filename)
        dest = dest / filename
    if dest.exists() and not dest.is_dir():
        if (replace is False
                or replace == "ask"
                and not click.confirm("Replace {}?".format(dest))):
            return str(dest)
    size = int(response.headers.get("content-length", 0))
    label = label.format(dest=dest, dest_basename=dest.name,
                         size=size/1024.0/1024)
    with click.open_file(str(dest), "wb") as f:
        content_iter = response.iter_content(chunk_size=chunk_size)
        with click.progressbar(content_iter, length=size/1024,
                               label=label) as bar:
            for chunk in bar:
                if chunk:
                    f.write(chunk)
                    f.flush()
    return str(dest)
def _buildvisitdir(kindpats):
    """Try to build an efficient visitdir function

    Return a visitdir function if it's built. Otherwise return None
    if there are unsupported patterns.

    >>> _buildvisitdir([('include', 'foo', '')])
    >>> _buildvisitdir([('relglob', 'foo', '')])
    >>> t = _buildvisitdir([
    ...     ('glob', 'a/b', ''),
    ...     ('glob', 'c/*.d', ''),
    ...     ('glob', 'e/**/*.c', ''),
    ...     ('re', '^f/(?!g)', ''), # no "$", only match prefix
    ...     ('re', '^h/(i|j)$', ''),
    ...     ('glob', 'i/a*/b*/c*', ''),
    ...     ('glob', 'i/a5/b7/d', ''),
    ...     ('glob', 'j/**.c', ''),
    ... ])
    >>> t('a')
    True
    >>> t('a/b')
    'all'
    >>> t('a/b/c')
    'all'
    >>> t('c')
    True
    >>> t('c/d')
    False
    >>> t('c/rc.d')
    'all'
    >>> t('c/rc.d/foo')
    'all'
    >>> t('e')
    True
    >>> t('e/a')
    True
    >>> t('e/a/b.c')
    True
    >>> t('e/a/b.d')
    True
    >>> t('f')
    True
    >>> t('f/g')
    False
    >>> t('f/g2')
    False
    >>> t('f/g/a')
    False
    >>> t('f/h')
    'all'
    >>> t('f/h/i')
    'all'
    >>> t('h/i')
    True
    >>> t('h/i/k')
    False
    >>> t('h/k')
    False
    >>> t('i')
    True
    >>> t('i/a1')
    True
    >>> t('i/b2')
    False
    >>> t('i/a/b2/c3')
    'all'
    >>> t('i/a/b2/d4')
    False
    >>> t('i/a5/b7/d')
    'all'
    >>> t('j/x/y')
    True
    >>> t('z')
    False
    """
    tree = _tree()
    for kind, pat, _source in kindpats:
        if kind == "glob":
            components = []
            for p in pat.split("/"):
                if "[" in p or "{" in p or "*" in p or "?" in p:
                    break
                components.append(p)
            prefix = "/".join(components)
            matchrecursive = prefix == pat
            tree.insert(
                prefix,
                matchrecursive=matchrecursive,
                globpats=_remainingpats(pat, prefix),
            )
        elif kind == "re":
            # Still try to get a plain prefix from the regular expression so we
            # can still have fast paths.
            if pat.startswith("^"):
                # "re" already matches from the beginning, unlike "relre"
                pat = pat[1:]
            components = []
            for p in pat.split("/"):
                if re.escape(p) != p:
                    # contains special characters
                    break
                components.append(p)
            prefix = "/".join(components)
            tree.insert(
                prefix, matchrecursive=False, repats=_remainingpats(pat, prefix)
            )
        else:
            # Unsupported kind
            return None
    return tree.visitdir