import os.path

def get_site_url (script_name) :
    """
        Get the URL that points to the site root (i.e. where style.css is) using the given value of SCRIPT_NAME

        /foo/bar/quux.py                -> /foo
        /~terom/qmsk.net/site/index.py  -> /~terom/qmsk.net
        None                            -> /
    """
    
    if script_name :
        return os.path.dirname(os.path.dirname(script_name))
    else :
        return "/"

def get_page_path (path_info, default) :
    """
        Get the path of the page that was requested, or the given default is empty/invalid.
        The path will never begin with an /.

        /quux       -> quux
        /           -> <default>
        None        -> <default>
    """
    
    if path_info :
        # remove prefixed slashes
        path_info = path_info.lstrip('/')

    if path_info :
        return path_info
    else :
        return default


class Request (object) :
    # The name of the site itself, this can be used to reference e.g. style.css
    site_url = None

    # The page root url, for links to pages
    page_root = None

    # The full path to the requested page
    page_path = None
    
    def __init__ (self, environ, default_page='main') :
        self.site_url = get_site_url(environ.get("SCRIPT_NAME"))
        self.page_root = environ.get("SCRIPT_NAME")
        self.page_path = get_page_path(environ.get("PATH_INFO"), default_page)
    
    def page_name_parts (self) :
        """
            Returns a list of page name components
        """

        return self.page_path.split('/')

    def page_name_prefixes (self) :
        """
            Iterate over the components of the page name, yielding (prefix, suffix) pairs
        """
        
        prefix = self.page_name_parts()
        suffix = []

        while prefix :
            yield ('/'.join(prefix), '/'.join(suffix))

            suffix.insert(0, prefix.pop(-1))