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"""Parse (absolute and relative) URLs.

See RFC 1808: "Relative Uniform Resource Locators", by R. Fielding,

UC Irvine, June 1995.

"""

__all__ = ["urlparse", "urlunparse", "urljoin"]

# A classification of schemes ('' means apply by default)

uses_relative = ['ftp', 'http', 'gopher', 'nntp', 'wais', 'file',

                 'https', 'shttp',

                 'prospero', 'rtsp', 'rtspu', '']

uses_netloc = ['ftp', 'http', 'gopher', 'nntp', 'telnet', 'wais',

               'file',

               'https', 'shttp', 'snews',

               'prospero', 'rtsp', 'rtspu', '']

non_hierarchical = ['gopher', 'hdl', 'mailto', 'news', 'telnet', 'wais',

                    'snews', 'sip',

                    ]

uses_params = ['ftp', 'hdl', 'prospero', 'http',

               'https', 'shttp', 'rtsp', 'rtspu', 'sip',

               '']

uses_query = ['http', 'wais',

              'https', 'shttp',

              'gopher', 'rtsp', 'rtspu', 'sip',

              '']

uses_fragment = ['ftp', 'hdl', 'http', 'gopher', 'news', 'nntp', 'wais',

                 'https', 'shttp', 'snews',

                 'file', 'prospero', '']

# Characters valid in scheme names

scheme_chars = ('abcdefghijklmnopqrstuvwxyz'

                'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

                '0123456789'

                '+-.')

MAX_CACHE_SIZE = 20

_parse_cache = {}

def clear_cache():

    """Clear the parse cache."""

    global _parse_cache

    _parse_cache = {}

def urlparse(url, scheme = '', allow_fragments = 1):

    """Parse a URL into 6 components:

    <scheme>://<netloc>/<path>;<params>?<query>#<fragment>

    Return a 6-tuple: (scheme, netloc, path, params, query, fragment).

    Note that we don't break the components up in smaller bits

    (e.g. netloc is a single string) and we don't expand % escapes."""

    key = url, scheme, allow_fragments

    cached = _parse_cache.get(key, None)

    if cached:

        return cached

    if len(_parse_cache) >= MAX_CACHE_SIZE: # avoid runaway growth

        clear_cache()

    netloc = path = params = query = fragment = ''

    i = url.find(':')

    if i > 0:

        if url[:i] == 'http': # optimize the common case

            scheme = url[:i].lower()

            url = url[i+1:]

            if url[:2] == '//':

                i = url.find('/', 2)

                if i < 0:

                    i = len(url)

                netloc = url[2:i]

                url = url[i:]

            if allow_fragments:

                i = url.rfind('#')

                if i >= 0:

                    fragment = url[i+1:]

                    url = url[:i]

            i = url.find('?')

            if i >= 0:

                query = url[i+1:]

                url = url[:i]

            i = url.find(';')

            if i >= 0:

                params = url[i+1:]

                url = url[:i]

            tuple = scheme, netloc, url, params, query, fragment

            _parse_cache[key] = tuple

            return tuple

        for c in url[:i]:

            if c not in scheme_chars:

                break

        else:

            scheme, url = url[:i].lower(), url[i+1:]

    if scheme in uses_netloc:

        if url[:2] == '//':

            i = url.find('/', 2)

            if i < 0:

                i = len(url)

            netloc, url = url[2:i], url[i:]

    if allow_fragments and scheme in uses_fragment:

        i = url.rfind('#')

        if i >= 0:

            url, fragment = url[:i], url[i+1:]

    if scheme in uses_query:

        i = url.find('?')

        if i >= 0:

            url, query = url[:i], url[i+1:]

    if scheme in uses_params:

        i = url.find(';')

        if i >= 0:

            url, params = url[:i], url[i+1:]

    tuple = scheme, netloc, url, params, query, fragment

    _parse_cache[key] = tuple

    return tuple

def urlunparse((scheme, netloc, url, params, query, fragment)):

    """Put a parsed URL back together again.  This may result in a

    slightly different, but equivalent URL, if the URL that was parsed

    originally had redundant delimiters, e.g. a ? with an empty query

    (the draft states that these are equivalent)."""

    if netloc or (scheme in uses_netloc and url[:2] == '//'):

        if url and url[:1] != '/': url = '/' + url

        url = '//' + (netloc or '') + url

    if scheme:

        url = scheme + ':' + url

    if params:

        url = url + ';' + params

    if query:

        url = url + '?' + query

    if fragment:

        url = url + '#' + fragment

    return url

def urljoin(base, url, allow_fragments = 1):

    """Join a base URL and a possibly relative URL to form an absolute

    interpretation of the latter."""

    if not base:

        return url

    if not url:

        return base

    bscheme, bnetloc, bpath, bparams, bquery, bfragment = \

            urlparse(base, '', allow_fragments)

    scheme, netloc, path, params, query, fragment = \

            urlparse(url, bscheme, allow_fragments)

    if scheme != bscheme or scheme not in uses_relative:

        return url

    if scheme in uses_netloc:

        if netloc:

            return urlunparse((scheme, netloc, path,

                               params, query, fragment))

        netloc = bnetloc

    if path[:1] == '/':

        return urlunparse((scheme, netloc, path,

                           params, query, fragment))

    if not path:

        if not params:

            params = bparams

            if not query:

                query = bquery

        return urlunparse((scheme, netloc, bpath,

                           params, query, fragment))

    segments = bpath.split('/')[:-1] + path.split('/')

    # XXX The stuff below is bogus in various ways...

    if segments[-1] == '.':

        segments[-1] = ''

    while '.' in segments:

        segments.remove('.')

    while 1:

        i = 1

        n = len(segments) - 1

        while i < n:

            if (segments[i] == '..'

                and segments[i-1] not in ('', '..')):

                del segments[i-1:i+1]

                break

            i = i+1

        else:

            break

    if segments == ['', '..']:

        segments[-1] = ''

    elif len(segments) >= 2 and segments[-1] == '..':

        segments[-2:] = ['']

    return urlunparse((scheme, netloc, '/'.join(segments),

                       params, query, fragment))

def urldefrag(url):

    """Removes any existing fragment from URL.

    Returns a tuple of the defragmented URL and the fragment.  If

    the URL contained no fragments, the second element is the

    empty string.

    """

    s, n, p, a, q, frag = urlparse(url)

    defrag = urlunparse((s, n, p, a, q, ''))

    return defrag, frag

test_input = """

      http://a/b/c/d

      g:h        = <URL:g:h>

      http:g     = <URL:http://a/b/c/g>

      http:      = <URL:http://a/b/c/d>

      g          = <URL:http://a/b/c/g>

      ./g        = <URL:http://a/b/c/g>

      g/         = <URL:http://a/b/c/g/>

      /g         = <URL:http://a/g>

      //g        = <URL:http://g>

      ?y         = <URL:http://a/b/c/d?y>

      g?y        = <URL:http://a/b/c/g?y>

      g?y/./x    = <URL:http://a/b/c/g?y/./x>

      .          = <URL:http://a/b/c/>

      ./         = <URL:http://a/b/c/>

      ..         = <URL:http://a/b/>

      ../        = <URL:http://a/b/>

      ../g       = <URL:http://a/b/g>

      ../..      = <URL:http://a/>

      ../../g    = <URL:http://a/g>

      ../../../g = <URL:http://a/../g>

      ./../g     = <URL:http://a/b/g>

      ./g/.      = <URL:http://a/b/c/g/>

      /./g       = <URL:http://a/./g>

      g/./h      = <URL:http://a/b/c/g/h>

      g/../h     = <URL:http://a/b/c/h>

      http:g     = <URL:http://a/b/c/g>

      http:      = <URL:http://a/b/c/d>

      http:?y         = <URL:http://a/b/c/d?y>

      http:g?y        = <URL:http://a/b/c/g?y>

      http:g?y/./x    = <URL:http://a/b/c/g?y/./x>

"""

# XXX The result for //g is actually http://g/; is this a problem?

def test():

    import sys

    base = ''

    if sys.argv[1:]:

        fn = sys.argv[1]

        if fn == '-':

            fp = sys.stdin

        else:

            fp = open(fn)

    else:

        import StringIO

        fp = StringIO.StringIO(test_input)

    while 1:

        line = fp.readline()

        if not line: break

        words = line.split()

        if not words:

            continue

        url = words[0]

        parts = urlparse(url)

        print '%-10s : %s' % (url, parts)

        abs = urljoin(base, url)

        if not base:

            base = abs

        wrapped = '<URL:%s>' % abs

        print '%-10s = %s' % (url, wrapped)

        if len(words) == 3 and words[1] == '=':

            if wrapped != words[2]:

                print 'EXPECTED', words[2], '!!!!!!!!!!'

if __name__ == '__main__':

    test()