from collections import defaultdict
from fs.errors import ResourceNotFoundError
from functools import wraps
import logging

from path import path
from django.conf import settings
from django.http import Http404

from xmodule.course_module import CourseDescriptor
from xmodule.modulestore import Location
from xmodule.modulestore.django import modulestore
from xmodule.modulestore.exceptions import ItemNotFoundError
from static_replace import replace_urls, try_staticfiles_lookup
from courseware.access import has_access
import branding

log = logging.getLogger(__name__)


def get_course_by_id(course_id):
    """
    Given a course id, return the corresponding course descriptor.

    If course_id is not valid, raises a 404.
    """
    try:
        course_loc = CourseDescriptor.id_to_location(course_id)
        return modulestore().get_instance(course_id, course_loc)
    except (KeyError, ItemNotFoundError):
        raise Http404("Course not found.")


def get_course_with_access(user, course_id, action):
    """
    Given a course_id, look up the corresponding course descriptor,
    check that the user has the access to perform the specified action
    on the course, and return the descriptor.

    Raises a 404 if the course_id is invalid, or the user doesn't have access.
    """
    course = get_course_by_id(course_id)
    if not has_access(user, course, action):
        # Deliberately return a non-specific error message to avoid
        # leaking info about access control settings
        raise Http404("Course not found.")
    return course


def get_opt_course_with_access(user, course_id, action):
    """
    Same as get_course_with_access, except that if course_id is None,
    return None without performing any access checks.
    """
    if course_id is None:
        return None
    return get_course_with_access(user, course_id, action)


def course_image_url(course):
    """Try to look up the image url for the course.  If it's not found,
    log an error and return the dead link"""
    path = course.metadata['data_dir'] + "/images/course_image.jpg"
    return try_staticfiles_lookup(path)

def get_course_about_section(course, section_key):
    """
    This returns the snippet of html to be rendered on the course about page,
    given the key for the section.

    Valid keys:
    - overview
    - title
    - university
    - number
    - short_description
    - description
    - key_dates (includes start, end, exams, etc)
    - video
    - course_staff_short
    - course_staff_extended
    - requirements
    - syllabus
    - textbook
    - faq
    - more_info
    """

    # Many of these are stored as html files instead of some semantic
    # markup. This can change without effecting this interface when we find a
    # good format for defining so many snippets of text/html.

# TODO: Remove number, instructors from this list
    if section_key in ['short_description', 'description', 'key_dates', 'video',
                       'course_staff_short', 'course_staff_extended',
                       'requirements', 'syllabus', 'textbook', 'faq', 'more_info',
                       'number', 'instructors', 'overview',
                       'effort', 'end_date', 'prerequisites']:
        try:
            with course.system.resources_fs.open(path("about") / section_key + ".html") as htmlFile:
                return replace_urls(htmlFile.read().decode('utf-8'),
                                    course.metadata['data_dir'])
        except ResourceNotFoundError:
            log.warning("Missing about section {key} in course {url}".format(
                key=section_key, url=course.location.url()))
            return None
    elif section_key == "title":
        return course.metadata.get('display_name', course.url_name)
    elif section_key == "university":
        return course.location.org
    elif section_key == "number":
        return course.number

    raise KeyError("Invalid about key " + str(section_key))


def get_course_info_section(course, section_key):
    """
    This returns the snippet of html to be rendered on the course info page,
    given the key for the section.

    Valid keys:
    - handouts
    - guest_handouts
    - updates
    - guest_updates
    """

    # Many of these are stored as html files instead of some semantic
    # markup. This can change without effecting this interface when we find a
    # good format for defining so many snippets of text/html.

    if section_key in ['handouts', 'guest_handouts', 'updates', 'guest_updates']:
        try:
            with course.system.resources_fs.open(path("info") / section_key + ".html") as htmlFile:
                return replace_urls(htmlFile.read().decode('utf-8'),
                                    course.metadata['data_dir'])
        except ResourceNotFoundError:
            log.exception("Missing info section {key} in course {url}".format(
                key=section_key, url=course.location.url()))
            return "! Info section missing !"

    raise KeyError("Invalid about key " + str(section_key))


# TODO: Fix this such that these are pulled in as extra course-specific tabs.
#       arjun will address this by the end of October if no one does so prior to
#       then.
def get_course_syllabus_section(course, section_key):
    """
    This returns the snippet of html to be rendered on the syllabus page,
    given the key for the section.

    Valid keys:
    - syllabus
    - guest_syllabus
    """

    # Many of these are stored as html files instead of some semantic
    # markup. This can change without effecting this interface when we find a
    # good format for defining so many snippets of text/html.

    if section_key in ['syllabus', 'guest_syllabus']:
        try:
            with course.system.resources_fs.open(path("syllabus") / section_key + ".html") as htmlFile:
                return replace_urls(htmlFile.read().decode('utf-8'),
                                    course.metadata['data_dir'])
        except ResourceNotFoundError:
            log.exception("Missing syllabus section {key} in course {url}".format(
                key=section_key, url=course.location.url()))
            return "! Syllabus missing !"

    raise KeyError("Invalid about key " + str(section_key))


def get_courses_by_university(user, domain=None):
    '''
    Returns dict of lists of courses available, keyed by course.org (ie university).
    Courses are sorted by course.number.
    '''
    # TODO: Clean up how 'error' is done.
    # filter out any courses that errored.
    visible_courses = branding.get_visible_courses(domain)

    universities = defaultdict(list)
    for course in visible_courses:
        if not has_access(user, course, 'see_exists'):
            continue
        universities[course.org].append(course)
    return universities
