import logging
import sys
from functools import partial

from django.conf import settings
from django.http import HttpResponse, Http404, HttpResponseBadRequest, HttpResponseForbidden
from django.core.urlresolvers import reverse
from django.contrib.auth.decorators import login_required
from mitxmako.shortcuts import render_to_response

from xmodule_modifiers import replace_static_urls, wrap_xmodule, save_module  # pylint: disable=F0401
from xmodule.error_module import ErrorDescriptor
from xmodule.errortracker import exc_info_to_str
from xmodule.exceptions import NotFoundError, ProcessingError
from xmodule.modulestore.django import modulestore
from xmodule.x_module import ModuleSystem
from xblock.runtime import DbModel

from lms.xblock.field_data import lms_field_data

from util.sandboxing import can_execute_unsafe_code

import static_replace
from .session_kv_store import SessionKeyValueStore
from .requests import render_from_lms
from .access import has_access
from ..utils import get_course_for_item

__all__ = ['preview_dispatch', 'preview_component']

log = logging.getLogger(__name__)


@login_required
def preview_dispatch(request, preview_id, location, dispatch=None):
    """
    Dispatch an AJAX action to a preview XModule

    Expects a POST request, and passes the arguments to the module

    preview_id (str): An identifier specifying which preview this module is used for
    location: The Location of the module to dispatch to
    dispatch: The action to execute
    """

    descriptor = modulestore().get_item(location)
    instance = load_preview_module(request, preview_id, descriptor)
    # Let the module handle the AJAX
    try:
        ajax_return = instance.handle_ajax(dispatch, request.POST)
        # Save any module data that has changed to the underlying KeyValueStore
        instance.save()

    except NotFoundError:
        log.exception("Module indicating to user that request doesn't exist")
        raise Http404

    except ProcessingError:
        log.warning("Module raised an error while processing AJAX request",
                    exc_info=True)
        return HttpResponseBadRequest()

    except:
        log.exception("error processing ajax call")
        raise

    return HttpResponse(ajax_return)


@login_required
def preview_component(request, location):
    "Return the HTML preview of a component"
    # TODO (vshnayder): change name from id to location in coffee+html as well.
    if not has_access(request.user, location):
        return HttpResponseForbidden()

    component = modulestore().get_item(location)

    component.get_html = wrap_xmodule(
        component.get_html,
        component,
        'xmodule_edit.html'
    )
    return render_to_response('component.html', {
        'preview': get_preview_html(request, component, 0),
        'editor': component.runtime.render(component, None, 'studio_view').content,
    })


def preview_module_system(request, preview_id, descriptor):
    """
    Returns a ModuleSystem for the specified descriptor that is specialized for
    rendering module previews.

    request: The active django request
    preview_id (str): An identifier specifying which preview this module is used for
    descriptor: An XModuleDescriptor
    """

    def preview_field_data(descriptor):
        "Helper method to create a DbModel from a descriptor"
        student_data = DbModel(SessionKeyValueStore(request))
        return lms_field_data(descriptor._field_data, student_data)

    course_id = get_course_for_item(descriptor.location).location.course_id
    return ModuleSystem(
        ajax_url=reverse('preview_dispatch', args=[preview_id, descriptor.location.url(), '']).rstrip('/'),
        # TODO (cpennington): Do we want to track how instructors are using the preview problems?
        track_function=lambda event_type, event: None,
        filestore=descriptor.system.resources_fs,
        get_module=partial(load_preview_module, request, preview_id),
        render_template=render_from_lms,
        debug=True,
        replace_urls=partial(static_replace.replace_static_urls, data_directory=None, course_id=course_id),
        user=request.user,
        xblock_field_data=preview_field_data,
        can_execute_unsafe_code=(lambda: can_execute_unsafe_code(course_id)),
        mixins=settings.XBLOCK_MIXINS,
        course_id=course_id,
        anonymous_student_id='student'
    )


def load_preview_module(request, preview_id, descriptor):
    """
    Return a preview XModule instantiated from the supplied descriptor.

    request: The active django request
    preview_id (str): An identifier specifying which preview this module is used for
    descriptor: An XModuleDescriptor
    """
    system = preview_module_system(request, preview_id, descriptor)
    try:
        module = descriptor.xmodule(system)
    except:
        log.debug("Unable to load preview module", exc_info=True)
        module = ErrorDescriptor.from_descriptor(
            descriptor,
            error_msg=exc_info_to_str(sys.exc_info())
        ).xmodule(system)

    # cdodge: Special case
    if module.location.category == 'static_tab':
        module.get_html = wrap_xmodule(
            module.get_html,
            module,
            "xmodule_tab_display.html",
        )
    else:
        module.get_html = wrap_xmodule(
            module.get_html,
            module,
            "xmodule_display.html",
        )

    # we pass a partially bogus course_id as we don't have the RUN information passed yet
    # through the CMS. Also the contentstore is also not RUN-aware at this point in time.
    module.get_html = replace_static_urls(
        module.get_html,
        getattr(module, 'data_dir', module.location.course),
        course_id=module.location.org + '/' + module.location.course + '/BOGUS_RUN_REPLACE_WHEN_AVAILABLE'
    )

    module.get_html = save_module(
        module.get_html,
        module
    )

    return module


def get_preview_html(request, descriptor, idx):
    """
    Returns the HTML returned by the XModule's student_view,
    specified by the descriptor and idx.
    """
    module = load_preview_module(request, str(idx), descriptor)
    return module.runtime.render(module, None, "student_view").content
