"""Parse (absolute and relative) URLs.

See RFC 1808: "Relative Uniform Resource Locators", by R. Fielding,
UC Irvine, June 1995.
"""

# Standard/builtin Python modules
import string
from string import joinfields, splitfields, rfind

# A classification of schemes ('' means apply by default)
uses_relative = ['ftp', 'http', 'gopher', 'nntp', 'wais', 'file',
		 'https', 'shttp',
		 'prospero', '']
uses_netloc = ['ftp', 'http', 'gopher', 'nntp', 'telnet', 'wais',
	       'file',
	       'https', 'shttp', 'snews',
	       'prospero', '']
non_hierarchical = ['gopher', 'hdl', 'mailto', 'news', 'telnet', 'wais',
		    'snews',
		    ]
uses_params = ['ftp', 'hdl', 'prospero', 'http',
	       'https', 'shttp',
	       '']
uses_query = ['http', 'wais',
	      'https', 'shttp',
	      'gopher',
	      '']
uses_fragment = ['ftp', 'hdl', 'http', 'gopher', 'news', 'nntp', 'wais',
		 'https', 'shttp', 'snews',
		 'file', 'prospero', '']

# Characters valid in scheme names
scheme_chars = string.letters + string.digits + '+-.'

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()
	find = string.find
	netloc = path = params = query = fragment = ''
	i = find(url, ':')
	if i > 0:
		if url[:i] == 'http': # optimize the common case
			scheme = string.lower(url[:i])
			url = url[i+1:]
			if url[:2] == '//':
				i = find(url, '/', 2)
				if i < 0:
					i = len(url)
				netloc = url[2:i]
				url = url[i:]
			if allow_fragments:
				i = string.rfind(url, '#')
				if i >= 0:
					fragment = url[i+1:]
					url = url[:i]
			i = find(url, '?')
			if i >= 0:
				query = url[i+1:]
				url = url[:i]
			i = find(url, ';')
			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 = string.lower(url[:i]), url[i+1:]
	if scheme in uses_netloc:
		if url[:2] == '//':
			i = find(url, '/', 2)
			if i < 0:
				i = len(url)
			netloc, url = url[2:i], url[i:]
	if allow_fragments and scheme in uses_fragment:
		i = string.rfind(url, '#')
		if i >= 0:
			url, fragment = url[:i], url[i+1:]
	if scheme in uses_query:
		i = find(url, '?')
		if i >= 0:
			url, query = url[:i], url[i+1:]
	if scheme in uses_params:
		i = find(url, ';')
		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[: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
	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 urlunparse((scheme, netloc, path,
				   params, query, fragment))
	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:
		return urlunparse((scheme, netloc, bpath,
				   params, query or bquery, fragment))
	i = rfind(bpath, '/')
	if i >= 0:
		path = bpath[:i] + '/' + path
	segments = splitfields(path, '/')
	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]:
				del segments[i-1:i+1]
				break
			i = i+1
		else:
			break
	if len(segments) == 2 and segments[1] == '..' and segments[0] == '':
		segments[-1] = ''
	elif len(segments) >= 2 and segments[-1] == '..':
		segments[-2:] = ['']
	return urlunparse((scheme, netloc, joinfields(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 = string.split(line)
		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()