from collections import defaultdict
from fs.errors import ResourceNotFoundError
import logging
import inspect

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

from edxmako.shortcuts import render_to_string
from xmodule.modulestore import ModuleStoreEnum
from opaque_keys.edx.keys import CourseKey
from xmodule.modulestore.django import modulestore
from xmodule.contentstore.content import StaticContent
from xmodule.modulestore.exceptions import ItemNotFoundError
from static_replace import replace_static_urls
from xmodule.modulestore import ModuleStoreEnum
from xmodule.x_module import STUDENT_VIEW
from microsite_configuration import microsite

from courseware.access import has_access
from courseware.model_data import FieldDataCache
from courseware.module_render import get_module
from student.models import CourseEnrollment
import branding

from opaque_keys.edx.keys import UsageKey

log = logging.getLogger(__name__)


def get_request_for_thread():
    """Walk up the stack, return the nearest first argument named "request"."""
    frame = None
    try:
        for f in inspect.stack()[1:]:
            frame = f[0]
            code = frame.f_code
            if code.co_varnames[:1] == ("request",):
                return frame.f_locals["request"]
            elif code.co_varnames[:2] == ("self", "request",):
                return frame.f_locals["request"]
    finally:
        del frame


def get_course(course_id, depth=0):
    """
    Given a course id, return the corresponding course descriptor.

    If the course does not exist, raises a ValueError.  This is appropriate
    for internal use.

    depth: The number of levels of children for the modulestore to cache.
    None means infinite depth.  Default is to fetch no children.
    """
    course = modulestore().get_course(course_id, depth=depth)
    if course is None:
        raise ValueError(u"Course not found: {0}".format(course_id))
    return course


# TODO please rename this function to get_course_by_key at next opportunity!
def get_course_by_id(course_key, depth=0):
    """
    Given a course id, return the corresponding course descriptor.

    If such a course does not exist, raises a 404.

    depth: The number of levels of children for the modulestore to cache. None means infinite depth
    """
    with modulestore().bulk_operations(course_key):
        course = modulestore().get_course(course_key, depth=depth)
    if course:
        return course
    else:
        raise Http404("Course not found.")


class UserNotEnrolled(Http404):
    def __init__(self, course_key):
        super(UserNotEnrolled, self).__init__()
        self.course_key = course_key


def get_course_with_access(user, action, course_key, depth=0, check_if_enrolled=False):
    """
    Given a course_key, 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_key is invalid, or the user doesn't have access.

    depth: The number of levels of children for the modulestore to cache. None means infinite depth

    check_if_enrolled: If true, additionally verifies that the user is either enrolled in the course
      or has staff access.
    """
    assert isinstance(course_key, CourseKey)
    course = get_course_by_id(course_key, depth=depth)

    if not has_access(user, action, course, course_key):
        # Deliberately return a non-specific error message to avoid
        # leaking info about access control settings
        raise Http404("Course not found.")

    if check_if_enrolled:
        # Verify that the user is either enrolled in the course or a staff member.
        # If user is not enrolled, raise UserNotEnrolled exception that will be caught by middleware.
        if not ((user.id and CourseEnrollment.is_enrolled(user, course_key)) or has_access(user, 'staff', course)):
            raise UserNotEnrolled(course_key)

    return course


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"""
    if course.static_asset_path or modulestore().get_modulestore_type(course.id) == ModuleStoreEnum.Type.xml:
        # If we are a static course with the course_image attribute
        # set different than the default, return that path so that
        # courses can use custom course image paths, otherwise just
        # return the default static path.
        url = '/static/' + (course.static_asset_path or getattr(course, 'data_dir', ''))
        if hasattr(course, 'course_image') and course.course_image != course.fields['course_image'].default:
            url += '/' + course.course_image
        else:
            url += '/images/course_image.jpg'
    elif course.course_image == '':
        # if course_image is empty the url will be blank as location
        # of the course_image does not exist
        url = ''
    else:
        loc = StaticContent.compute_location(course.id, course.course_image)
        url = StaticContent.serialize_asset_key_with_slash(loc)
    return url


def find_file(filesystem, dirs, filename):
    """
    Looks for a filename in a list of dirs on a filesystem, in the specified order.

    filesystem: an OSFS filesystem
    dirs: a list of path objects
    filename: a string

    Returns d / filename if found in dir d, else raises ResourceNotFoundError.
    """
    for directory in dirs:
        filepath = path(directory) / filename
        if filesystem.exists(filepath):
            return filepath
    raise ResourceNotFoundError(u"Could not find {0}".format(filename))


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
    - ocw_links
    """

    # 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', 'ocw_links']:

        try:

            request = get_request_for_thread()

            loc = course.location.replace(category='about', name=section_key)

            # Use an empty cache
            field_data_cache = FieldDataCache([], course.id, request.user)
            about_module = get_module(
                request.user,
                request,
                loc,
                field_data_cache,
                log_if_not_found=False,
                wrap_xmodule_display=False,
                static_asset_path=course.static_asset_path,
                course=course
            )

            html = ''

            if about_module is not None:
                try:
                    html = about_module.render(STUDENT_VIEW).content
                except Exception:  # pylint: disable=broad-except
                    html = render_to_string('courseware/error-message.html', None)
                    log.exception(
                        u"Error rendering course={course}, section_key={section_key}".format(
                            course=course, section_key=section_key
                        ))
            return html

        except ItemNotFoundError:
            log.warning(
                u"Missing about section {key} in course {url}".format(key=section_key, url=course.location.to_deprecated_string())
            )
            return None
    elif section_key == "title":
        return course.display_name_with_default
    elif section_key == "university":
        return course.display_org_with_default
    elif section_key == "number":
        return course.display_number_with_default

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


def get_course_info_section_module(request, course, section_key):
    """
    This returns the course info module for a given section_key.

    Valid keys:
    - handouts
    - guest_handouts
    - updates
    - guest_updates
    """
    usage_key = course.id.make_usage_key('course_info', section_key)

    # Use an empty cache
    field_data_cache = FieldDataCache([], course.id, request.user)

    return get_module(
        request.user,
        request,
        usage_key,
        field_data_cache,
        log_if_not_found=False,
        wrap_xmodule_display=False,
        static_asset_path=course.static_asset_path,
        course=course
    )


def get_course_info_section(request, 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
    """
    info_module = get_course_info_section_module(request, course, section_key)

    html = ''
    if info_module is not None:
        try:
            html = info_module.render(STUDENT_VIEW).content
        except Exception:  # pylint: disable=broad-except
            html = render_to_string('courseware/error-message.html', None)
            log.exception(
                u"Error rendering course={course}, section_key={section_key}".format(
                    course=course, section_key=section_key
                ))

    return html


# 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:
            filesys = course.system.resources_fs
            # first look for a run-specific version
            dirs = [path("syllabus") / course.url_name, path("syllabus")]
            filepath = find_file(filesys, dirs, section_key + ".html")
            with filesys.open(filepath) as html_file:
                return replace_static_urls(
                    html_file.read().decode('utf-8'),
                    getattr(course, 'data_dir', None),
                    course_id=course.id,
                    static_asset_path=course.static_asset_path,
                )
        except ResourceNotFoundError:
            log.exception(
                u"Missing syllabus section {key} in course {url}".format(key=section_key, url=course.location.to_deprecated_string())
            )
            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 = get_courses(user, domain)

    universities = defaultdict(list)
    for course in visible_courses:
        universities[course.org].append(course)

    return universities


def get_courses(user, domain=None):
    '''
    Returns a list of courses available, sorted by course.number
    '''
    courses = branding.get_visible_courses()

    permission_name = microsite.get_value(
        'COURSE_CATALOG_VISIBILITY_PERMISSION',
        settings.COURSE_CATALOG_VISIBILITY_PERMISSION
    )

    courses = [c for c in courses if has_access(user, permission_name, c)]

    courses = sorted(courses, key=lambda course: course.number)

    return courses


def sort_by_announcement(courses):
    """
    Sorts a list of courses by their announcement date. If the date is
    not available, sort them by their start date.
    """

    # Sort courses by how far are they from they start day
    key = lambda course: course.sorting_score
    courses = sorted(courses, key=key)

    return courses


def sort_by_start_date(courses):
    """
    Returns a list of courses sorted by their start date, latest first.
    """
    courses = sorted(
        courses,
        key=lambda course: (course.has_ended(), course.start is None, course.start),
        reverse=False
    )

    return courses


def get_cms_course_link(course, page='course'):
    """
    Returns a link to course_index for editing the course in cms,
    assuming that the course is actually cms-backed.
    """
    # This is fragile, but unfortunately the problem is that within the LMS we
    # can't use the reverse calls from the CMS
    return u"//{}/{}/{}".format(settings.CMS_BASE, page, unicode(course.id))


def get_cms_block_link(block, page):
    """
    Returns a link to block_index for editing the course in cms,
    assuming that the block is actually cms-backed.
    """
    # This is fragile, but unfortunately the problem is that within the LMS we
    # can't use the reverse calls from the CMS
    return u"//{}/{}/{}".format(settings.CMS_BASE, page, block.location)


def get_studio_url(course, page):
    """
    Get the Studio URL of the page that is passed in.

    Args:
        course (CourseDescriptor)
    """
    is_studio_course = course.course_edit_method == "Studio"
    is_mongo_course = modulestore().get_modulestore_type(course.id) != ModuleStoreEnum.Type.xml
    studio_link = None
    if is_studio_course and is_mongo_course:
        studio_link = get_cms_course_link(course, page)
    return studio_link


def get_problems_in_section(section):
    """
    This returns a dict having problems in a section.
    Returning dict has problem location as keys and problem
    descriptor as values.
    """

    problem_descriptors = defaultdict()
    if not isinstance(section, UsageKey):
        section_key = UsageKey.from_string(section)
    else:
        section_key = section
    # it will be a Mongo performance boost, if you pass in a depth=3 argument here
    # as it will optimize round trips to the database to fetch all children for the current node
    section_descriptor = modulestore().get_item(section_key, depth=3)

    # iterate over section, sub-section, vertical
    for subsection in section_descriptor.get_children():
        for vertical in subsection.get_children():
            for component in vertical.get_children():
                if component.location.category == 'problem' and getattr(component, 'has_score', False):
                    problem_descriptors[unicode(component.location)] = component

    return problem_descriptors
