import re
import urllib
import urlparse
from email.Utils import formatdate

from django.utils.encoding import smart_str, force_unicode
from django.utils.functional import allow_lazy

ETAG_MATCH = re.compile(r'(?:W/)?"((?:\\.|[^"])*)"')

def urlquote(url, safe='/'):
    """
    A version of Python's urllib.quote() function that can operate on unicode
    strings. The url is first UTF-8 encoded before quoting. The returned string
    can safely be used as part of an argument to a subsequent iri_to_uri() call
    without double-quoting occurring.
    """
    return force_unicode(urllib.quote(smart_str(url), safe))

urlquote = allow_lazy(urlquote, unicode)

def urlquote_plus(url, safe=''):
    """
    A version of Python's urllib.quote_plus() function that can operate on
    unicode strings. The url is first UTF-8 encoded before quoting. The
    returned string can safely be used as part of an argument to a subsequent
    iri_to_uri() call without double-quoting occurring.
    """
    return force_unicode(urllib.quote_plus(smart_str(url), safe))
urlquote_plus = allow_lazy(urlquote_plus, unicode)

def urlencode(query, doseq=0):
    """
    A version of Python's urllib.urlencode() function that can operate on
    unicode strings. The parameters are first case to UTF-8 encoded strings and
    then encoded as per normal.
    """
    if hasattr(query, 'items'):
        query = query.items()
    return urllib.urlencode(
        [(smart_str(k),
         isinstance(v, (list,tuple)) and [smart_str(i) for i in v] or smart_str(v))
            for k, v in query],
        doseq)

def cookie_date(epoch_seconds=None):
    """
    Formats the time to ensure compatibility with Netscape's cookie standard.

    Accepts a floating point number expressed in seconds since the epoch, in
    UTC - such as that outputted by time.time(). If set to None, defaults to
    the current time.

    Outputs a string in the format 'Wdy, DD-Mon-YYYY HH:MM:SS GMT'.
    """
    rfcdate = formatdate(epoch_seconds)
    return '%s-%s-%s GMT' % (rfcdate[:7], rfcdate[8:11], rfcdate[12:25])

def http_date(epoch_seconds=None):
    """
    Formats the time to match the RFC1123 date format as specified by HTTP
    RFC2616 section 3.3.1.

    Accepts a floating point number expressed in seconds since the epoch, in
    UTC - such as that outputted by time.time(). If set to None, defaults to
    the current time.

    Outputs a string in the format 'Wdy, DD Mon YYYY HH:MM:SS GMT'.
    """
    rfcdate = formatdate(epoch_seconds)
    return '%s GMT' % rfcdate[:25]

# Base 36 functions: useful for generating compact URLs

def base36_to_int(s):
    """
    Converts a base 36 string to an ``int``. To prevent
    overconsumption of server resources, raises ``ValueError` if the
    input is longer than 13 base36 digits (13 digits is sufficient to
    base36-encode any 64-bit integer).
    """
    if len(s) > 13:
        raise ValueError("Base36 input too large")
    return int(s, 36)

def int_to_base36(i):
    """
    Converts an integer to a base36 string
    """
    digits = "0123456789abcdefghijklmnopqrstuvwxyz"
    factor = 0
    # Find starting factor
    while True:
        factor += 1
        if i < 36 ** factor:
            factor -= 1
            break
    base36 = []
    # Construct base36 representation
    while factor >= 0:
        j = 36 ** factor
        base36.append(digits[i / j])
        i = i % j
        factor -= 1
    return ''.join(base36)

def parse_etags(etag_str):
    """
    Parses a string with one or several etags passed in If-None-Match and
    If-Match headers by the rules in RFC 2616. Returns a list of etags
    without surrounding double quotes (") and unescaped from \<CHAR>.
    """
    etags = ETAG_MATCH.findall(etag_str)
    if not etags:
        # etag_str has wrong format, treat it as an opaque string then
        return [etag_str]
    etags = [e.decode('string_escape') for e in etags]
    return etags

def quote_etag(etag):
    """
    Wraps a string in double quotes escaping contents as necesary.
    """
    return '"%s"' % etag.replace('\\', '\\\\').replace('"', '\\"')

def is_safe_url(url, host=None):
    """
    Return ``True`` if the url is a safe redirection (i.e. it doesn't point to
    a different host and uses a safe scheme).

    Always returns ``False`` on an empty url.
    """
    if not url:
        return False
    # Chrome treats \ completely as /
    url = url.replace('\\', '/')
    # Chrome considers any URL with more than two slashes to be absolute, but
    # urlaprse is not so flexible. Treat any url with three slashes as unsafe.
    if url.startswith('///'):
        return False
    url_info = urlparse.urlparse(url)
    # Forbid URLs like http:///example.com - with a scheme, but without a hostname.
    # In that URL, example.com is not the hostname but, a path component. However,
    # Chrome will still consider example.com to be the hostname, so we must not
    # allow this syntax.
    if not url_info[1] and url_info[0]:
        return False
    return (not url_info[1] or url_info[1] == host) and \
        (not url_info[0] or url_info[0] in ['http', 'https'])