import os, sys, re
import wsgiref.handlers

from google.appengine.ext.webapp import template
from google.appengine.ext import webapp
from google.appengine.api import urlfetch

BASE_URL = "http://a2parking.appspot.com/"
PARKING_API_URL = \
    "http://www.a2dda.org/parking__transportation/available_parking_spots/"

PARKING_LOCATIONS_RE = re.compile(">[\s\w\.:]+</td>[\r\n\s]*<td>[\s\w\.]+<",
    re.MULTILINE)

def xml_response(handler, page, templatevalues=None):
    """
    Renders an XML response using a provided template page and values
    """
    path = os.path.join(os.path.dirname(__file__), page)
    handler.response.headers["Content-Type"] = "text/xml"
    handler.response.out.write(template.render(path, templatevalues))

def fetch_parking():
    result = urlfetch.fetch(PARKING_API_URL)
    if result.status_code != 200:
        return None
    return result.content

class ParkingSpotsPage(webapp.RequestHandler):
    """
    Accepts input digits from the caller, fetches the parking info from an
    external site, and reads back the number of spots to the caller
    """
    def get(self):
        self.post()
    
    def _error(self, msg, redirecturl=None):
        templatevalues = {
            'msg': msg,
            'redirecturl': redirecturl
        }
        xml_response(self, 'error.xml', templatevalues)
    
    def post(self):
        location = self.request.get('Digits')
        try:
            location = location.replace('#', '').replace('*', '')[:1]
            location = int(location)
        except:
            self._error("Invalid parking location.", BASE_URL)
            return
        
        parkingpage = fetch_parking()
        if not parkingpage:
            self._error("Error fetching parking page. Good Bye.")
            return
        
        locations = PARKING_LOCATIONS_RE.findall(parkingpage)
        if not locations:
            self._error("Error parsing parking spots.", BASE_URL)
            return
        if location >= len(locations):
            self._error("Invalid parking location.", BASE_URL)
            return
        
        try:
            name = locations[location][1:].split(':')[0]
            spots = locations[location].\
                split("<td>")[1][1:].split('<')[0].strip('.')
            spots = int(spots)
        except:
            self._error("Error parsing parking spots.", BASE_URL)
            return
        
        templatevalues = {
            'name': name,
            'spots': spots,
        }
        xml_response(self, 'spots.xml', templatevalues)
        

class ParkingLocationPage(webapp.RequestHandler):
    """
    Initial user greeting.  Fetches the parking locations and asks the user
    to select a location.  Setup to work with less than 10 locations.
    """
    def get(self):
        self.post()
    
    def post(self):
        parkingpage = fetch_parking()
        if not parkingpage:
            self._error("Error fetching parking page. Good Bye.")
            return
        
        l = PARKING_LOCATIONS_RE.findall(parkingpage)
        if not l:
            self._error("Error parsing parking locations.", BASE_URL)
            return
        locations = ''
        for i, p in enumerate(l):
            locations += '<Say>Press %d for ' % i
            locations += p[1:].split(':')[0] + '</Say>\n'
        
        templatevalues = {
            'locations': locations,
            'postprefix': BASE_URL,
        }
        xml_response(self, 'locations.xml', templatevalues)

def main():
    application = webapp.WSGIApplication([ \
        ('/', ParkingLocationPage),
        ('/spots', ParkingSpotsPage)],
        debug=True)
    wsgiref.handlers.CGIHandler().run(application)

if __name__ == "__main__":
    main()