from fs.errors import ResourceNotFoundError
import time
import logging
import requests
from lxml import etree

from xmodule.util.decorators import lazyproperty
from xmodule.graders import load_grading_policy
from xmodule.modulestore import Location
from xmodule.seq_module import SequenceDescriptor, SequenceModule
from xmodule.timeparse import parse_time, stringify_time

log = logging.getLogger(__name__)

class CourseDescriptor(SequenceDescriptor):
    module_class = SequenceModule

    class Textbook:
        def __init__(self, title, book_url):
            self.title = title
            self.book_url = book_url
            self.table_of_contents = self._get_toc_from_s3()

        @classmethod
        def from_xml_object(cls, xml_object):
            return cls(xml_object.get('title'), xml_object.get('book_url'))

        @property
        def table_of_contents(self):
            return self.table_of_contents

        def _get_toc_from_s3(self):
            """
            Accesses the textbook's table of contents (default name "toc.xml") at the URL self.book_url

            Returns XML tree representation of the table of contents
            """
            toc_url = self.book_url + 'toc.xml'

            # Get the table of contents from S3
            log.info("Retrieving textbook table of contents from %s" % toc_url)
            try:
                r = requests.get(toc_url)
            except Exception as err:
                msg = 'Error %s: Unable to retrieve textbook table of contents at %s' % (err, toc_url)
                log.error(msg)
                raise Exception(msg)

            # TOC is XML. Parse it
            try:
                table_of_contents = etree.fromstring(r.text)
            except Exception as err:
                msg = 'Error %s: Unable to parse XML for textbook table of contents at %s' % (err, toc_url)
                log.error(msg)
                raise Exception(msg)

            return table_of_contents


    def __init__(self, system, definition=None, **kwargs):
        super(CourseDescriptor, self).__init__(system, definition, **kwargs)
        self.textbooks = self.definition['data']['textbooks']

        msg = None
        if self.start is None:
            msg = "Course loaded without a valid start date. id = %s" % self.id
            # hack it -- start in 1970
            self.metadata['start'] = stringify_time(time.gmtime(0))
            log.critical(msg)
            system.error_tracker(msg)

        self.enrollment_start = self._try_parse_time("enrollment_start")
        self.enrollment_end = self._try_parse_time("enrollment_end")

        # NOTE: relies on the modulestore to call set_grading_policy() right after
        # init.  (Modulestore is in charge of figuring out where to load the policy from)


    def set_grading_policy(self, policy_str):
        """Parse the policy specified in policy_str, and save it"""
        try:
            self._grading_policy = load_grading_policy(policy_str)
        except:
            self.system.error_tracker("Failed to load grading policy")
            # Setting this to an empty dictionary will lead to errors when
            # grading needs to happen, but should allow course staff to see
            # the error log.
            self._grading_policy = {}


    @classmethod
    def definition_from_xml(cls, xml_object, system):
        textbooks = []
        for textbook in xml_object.findall("textbook"):
            textbooks.append(cls.Textbook.from_xml_object(textbook))
            xml_object.remove(textbook)
        definition =  super(CourseDescriptor, cls).definition_from_xml(xml_object, system)
        definition.setdefault('data', {})['textbooks'] = textbooks
        return definition

    def has_started(self):
        return time.gmtime() > self.start

    @property
    def grader(self):
        return self._grading_policy['GRADER']

    @property
    def grade_cutoffs(self):
        return self._grading_policy['GRADE_CUTOFFS']

    @lazyproperty
    def grading_context(self):
        """
        This returns a dictionary with keys necessary for quickly grading
        a student. They are used by grades.grade()

        The grading context has two keys:
        graded_sections - This contains the sections that are graded, as
            well as all possible children modules that can affect the
            grading. This allows some sections to be skipped if the student
            hasn't seen any part of it.

            The format is a dictionary keyed by section-type. The values are
            arrays of dictionaries containing
                "section_descriptor" : The section descriptor
                "xmoduledescriptors" : An array of xmoduledescriptors that
                    could possibly be in the section, for any student

        all_descriptors - This contains a list of all xmodules that can
            effect grading a student. This is used to efficiently fetch
            all the xmodule state for a StudentModuleCache without walking
            the descriptor tree again.


        """

        all_descriptors = []
        graded_sections = {}

        def yield_descriptor_descendents(module_descriptor):
            for child in module_descriptor.get_children():
                yield child
                for module_descriptor in yield_descriptor_descendents(child):
                    yield module_descriptor

        for c in self.get_children():
            sections = []
            for s in c.get_children():
                if s.metadata.get('graded', False):
                    xmoduledescriptors = list(yield_descriptor_descendents(s))

                    # The xmoduledescriptors included here are only the ones that have scores.
                    section_description = { 'section_descriptor' : s, 'xmoduledescriptors' : filter(lambda child: child.has_score, xmoduledescriptors) }

                    section_format = s.metadata.get('format', "")
                    graded_sections[ section_format ] = graded_sections.get( section_format, [] ) + [section_description]

                    all_descriptors.extend(xmoduledescriptors)
                    all_descriptors.append(s)

        return { 'graded_sections' : graded_sections,
                 'all_descriptors' : all_descriptors,}


    @staticmethod
    def make_id(org, course, url_name):
        return '/'.join([org, course, url_name])

    @staticmethod
    def id_to_location(course_id):
        '''Convert the given course_id (org/course/name) to a location object.
        Throws ValueError if course_id is of the wrong format.
        '''
        org, course, name = course_id.split('/')
        return Location('i4x', org, course, 'course', name)

    @staticmethod
    def location_to_id(location):
        '''Convert a location of a course to a course_id.  If location category
        is not "course", raise a ValueError.

        location: something that can be passed to Location
        '''
        loc = Location(location)
        if loc.category != "course":
            raise ValueError("{0} is not a course location".format(loc))
        return "/".join([loc.org, loc.course, loc.name])


    @property
    def id(self):
        """Return the course_id for this course"""
        return self.location_to_id(self.location)

    @property
    def start_date_text(self):
        return time.strftime("%b %d, %Y", self.start)

    @property
    def title(self):
        return self.display_name

    @property
    def number(self):
        return self.location.course

    @property
    def wiki_slug(self):
        return self.location.course

    @property
    def org(self):
        return self.location.org

