"""
xModule implementation of a learning sequence
"""

# pylint: disable=abstract-method
import collections
from datetime import datetime
import json
import logging
from pkg_resources import resource_string
from pytz import UTC

from lxml import etree
from xblock.core import XBlock
from xblock.fields import Integer, Scope, Boolean, String
from xblock.fragment import Fragment

from .exceptions import NotFoundError
from .fields import Date
from .mako_module import MakoModuleDescriptor
from .progress import Progress
from .x_module import XModule, STUDENT_VIEW
from .xml_module import XmlDescriptor

log = logging.getLogger(__name__)

try:
    import newrelic.agent
except ImportError:
    newrelic = None  # pylint: disable=invalid-name

# HACK: This shouldn't be hard-coded to two types
# OBSOLETE: This obsoletes 'type'
class_priority = ['video', 'problem']

# Make '_' a no-op so we can scrape strings. Using lambda instead of
#  `django.utils.translation.ugettext_noop` because Django cannot be imported in this file
_ = lambda text: text


class SequenceFields(object):
    has_children = True

    # NOTE: Position is 1-indexed.  This is silly, but there are now student
    # positions saved on prod, so it's not easy to fix.
    position = Integer(help="Last tab viewed in this sequence", scope=Scope.user_state)

    due = Date(
        display_name=_("Due Date"),
        help=_("Enter the date by which problems are due."),
        scope=Scope.settings,
    )

    hide_after_due = Boolean(
        display_name=_("Hide sequence content After Due Date"),
        help=_(
            "If set, the sequence content is hidden for non-staff users after the due date has passed."
        ),
        default=False,
        scope=Scope.settings,
    )

    is_entrance_exam = Boolean(
        display_name=_("Is Entrance Exam"),
        help=_(
            "Tag this course module as an Entrance Exam. "
            "Note, you must enable Entrance Exams for this course setting to take effect."
        ),
        default=False,
        scope=Scope.settings,
    )


class ProctoringFields(object):
    """
    Fields that are specific to Proctored or Timed Exams
    """
    is_time_limited = Boolean(
        display_name=_("Is Time Limited"),
        help=_(
            "This setting indicates whether students have a limited time"
            " to view or interact with this courseware component."
        ),
        default=False,
        scope=Scope.settings,
    )

    default_time_limit_minutes = Integer(
        display_name=_("Time Limit in Minutes"),
        help=_(
            "The number of minutes available to students for viewing or interacting with this courseware component."
        ),
        default=None,
        scope=Scope.settings,
    )

    is_proctored_enabled = Boolean(
        display_name=_("Is Proctoring Enabled"),
        help=_(
            "This setting indicates whether this exam is a proctored exam."
        ),
        default=False,
        scope=Scope.settings,
    )

    exam_review_rules = String(
        display_name=_("Software Secure Review Rules"),
        help=_(
            "This setting indicates what rules the proctoring team should follow when viewing the videos."
        ),
        default='',
        scope=Scope.settings,
    )

    is_practice_exam = Boolean(
        display_name=_("Is Practice Exam"),
        help=_(
            "This setting indicates whether this exam is for testing purposes only. Practice exams are not verified."
        ),
        default=False,
        scope=Scope.settings,
    )

    def _get_course(self):
        """
        Return course by course id.
        """
        return self.descriptor.runtime.modulestore.get_course(self.course_id)  # pylint: disable=no-member

    @property
    def is_timed_exam(self):
        """
        Alias the permutation of above fields that corresponds to un-proctored timed exams
        to the more clearly-named is_timed_exam
        """
        return not self.is_proctored_enabled and not self.is_practice_exam and self.is_time_limited

    @property
    def is_proctored_exam(self):
        """ Alias the is_proctored_enabled field to the more legible is_proctored_exam """
        return self.is_proctored_enabled

    @property
    def allow_proctoring_opt_out(self):
        """
        Returns true if the learner should be given the option to choose between
        taking a proctored exam, or opting out to take the exam without proctoring.
        """
        return self._get_course().allow_proctoring_opt_out

    @is_proctored_exam.setter
    def is_proctored_exam(self, value):
        """ Alias the is_proctored_enabled field to the more legible is_proctored_exam """
        self.is_proctored_enabled = value


@XBlock.wants('proctoring')
@XBlock.wants('verification')
@XBlock.wants('milestones')
@XBlock.wants('credit')
@XBlock.needs('user')
@XBlock.needs('bookmarks')
class SequenceModule(SequenceFields, ProctoringFields, XModule):
    """
    Layout module which lays out content in a temporal sequence
    """
    js = {
        'js': [resource_string(__name__, 'js/src/sequence/display.js')],
    }
    css = {
        'scss': [resource_string(__name__, 'css/sequence/display.scss')],
    }
    js_module_name = "Sequence"

    def __init__(self, *args, **kwargs):
        super(SequenceModule, self).__init__(*args, **kwargs)

        # If position is specified in system, then use that instead.
        position = getattr(self.system, 'position', None)
        if position is not None:
            assert isinstance(position, int)
            self.position = self.system.position

    def get_progress(self):
        ''' Return the total progress, adding total done and total available.
        (assumes that each submodule uses the same "units" for progress.)
        '''
        # TODO: Cache progress or children array?
        children = self.get_children()
        progresses = [child.get_progress() for child in children]
        progress = reduce(Progress.add_counts, progresses, None)
        return progress

    def handle_ajax(self, dispatch, data):  # TODO: bounds checking
        ''' get = request.POST instance '''
        if dispatch == 'goto_position':
            # set position to default value if either 'position' argument not
            # found in request or it is a non-positive integer
            position = data.get('position', u'1')
            if position.isdigit() and int(position) > 0:
                self.position = int(position)
            else:
                self.position = 1
            return json.dumps({'success': True})

        raise NotFoundError('Unexpected dispatch type')

    @classmethod
    def verify_current_content_visibility(cls, date, hide_after_date):
        """
        Returns whether the content visibility policy passes
        for the given date and hide_after_date values and
        the current date-time.
        """
        return (
            not date or
            not hide_after_date or
            datetime.now(UTC) < date
        )

    def student_view(self, context):
        context = context or {}
        self._capture_basic_metrics()
        banner_text = None
        special_html_view = self._hidden_content_student_view(context) or self._special_exam_student_view()
        if special_html_view:
            masquerading_as_specific_student = context.get('specific_masquerade', False)
            banner_text, special_html = special_html_view
            if special_html and not masquerading_as_specific_student:
                return Fragment(special_html)
        else:
            banner_text = self._gated_content_staff_banner()
        return self._student_view(context, banner_text)

    def _special_exam_student_view(self):
        """
        Checks whether this sequential is a special exam.  If so, returns
        a banner_text or the fragment to display depending on whether
        staff is masquerading.
        """
        if self.is_time_limited:
            special_exam_html = self._time_limited_student_view()
            if special_exam_html:
                banner_text = _("This exam is hidden from the learner.")
                return banner_text, special_exam_html

    def _hidden_content_student_view(self, context):
        """
        Checks whether the content of this sequential is hidden from the
        runtime user. If so, returns a banner_text or the fragment to
        display depending on whether staff is masquerading.
        """
        course = self._get_course()
        if not self._can_user_view_content(course):
            if course.self_paced:
                banner_text = _("Because the course has ended, this assignment is hidden from the learner.")
            else:
                banner_text = _("Because the due date has passed, this assignment is hidden from the learner.")

            hidden_content_html = self.system.render_template(
                'hidden_content.html',
                {
                    'self_paced': course.self_paced,
                    'progress_url': context.get('progress_url'),
                }
            )

            return banner_text, hidden_content_html

    def _gated_content_staff_banner(self):
        """
        Checks whether the content is gated for learners. If so,
        returns a banner_text depending on whether user is staff.
        """
        milestones_service = self.runtime.service(self, 'milestones')
        if milestones_service:
            content_milestones = milestones_service.get_course_content_milestones(
                self.course_id, self.location, 'requires'
            )
            banner_text = _('This subsection is unlocked for learners when they meet the prerequisite requirements.')
            if content_milestones and self.runtime.user_is_staff:
                return banner_text

    def _can_user_view_content(self, course):
        """
        Returns whether the runtime user can view the content
        of this sequential.
        """
        hidden_date = course.end if course.self_paced else self.due
        return (
            self.runtime.user_is_staff or
            self.verify_current_content_visibility(hidden_date, self.hide_after_due)
        )

    def _student_view(self, context, banner_text=None):
        """
        Returns the rendered student view of the content of this
        sequential.  If banner_text is given, it is added to the
        content.
        """
        display_items = self.get_display_items()
        self._update_position(context, len(display_items))

        fragment = Fragment()
        params = {
            'items': self._render_student_view_for_items(context, display_items, fragment),
            'element_id': self.location.html_id(),
            'item_id': self.location.to_deprecated_string(),
            'position': self.position,
            'tag': self.location.category,
            'ajax_url': self.system.ajax_url,
            'next_url': context.get('next_url'),
            'prev_url': context.get('prev_url'),
            'banner_text': banner_text,
        }
        fragment.add_content(self.system.render_template("seq_module.html", params))

        self._capture_full_seq_item_metrics(display_items)
        self._capture_current_unit_metrics(display_items)

        return fragment

    def _update_position(self, context, number_of_display_items):
        """
        Update the user's sequential position given the context and the
        number_of_display_items
        """
        # If we're rendering this sequence, but no position is set yet,
        # or exceeds the length of the displayable items,
        # default the position to the first element
        if context.get('requested_child') == 'first':
            self.position = 1
        elif context.get('requested_child') == 'last':
            self.position = number_of_display_items or 1
        elif self.position is None or self.position > number_of_display_items:
            self.position = 1

    def _render_student_view_for_items(self, context, display_items, fragment):
        """
        Updates the given fragment with rendered student views of the given
        display_items.  Returns a list of dict objects with information about
        the given display_items.
        """
        bookmarks_service = self.runtime.service(self, "bookmarks")
        context["username"] = self.runtime.service(self, "user").get_current_user().opt_attrs['edx-platform.username']
        display_names = [
            self.get_parent().display_name_with_default,
            self.display_name_with_default
        ]
        contents = []
        for item in display_items:
            is_bookmarked = bookmarks_service.is_bookmarked(usage_key=item.scope_ids.usage_id)
            context["bookmarked"] = is_bookmarked

            rendered_item = item.render(STUDENT_VIEW, context)
            fragment.add_frag_resources(rendered_item)

            iteminfo = {
                'content': rendered_item.content,
                'page_title': getattr(item, 'tooltip_title', ''),
                'type': item.get_icon_class(),
                'id': item.scope_ids.usage_id.to_deprecated_string(),
                'bookmarked': is_bookmarked,
                'path': " > ".join(display_names + [item.display_name_with_default]),
            }

            contents.append(iteminfo)

        return contents

    def _locations_in_subtree(self, node):
        """
        The usage keys for all descendants of an XBlock/XModule as a flat list.

        Includes the location of the node passed in.
        """
        stack = [node]
        locations = []

        while stack:
            curr = stack.pop()
            locations.append(curr.location)
            if curr.has_children:
                stack.extend(curr.get_children())

        return locations

    def _capture_basic_metrics(self):
        """
        Capture basic information about this sequence in New Relic.
        """
        if not newrelic:
            return
        newrelic.agent.add_custom_parameter('seq.block_id', unicode(self.location))
        newrelic.agent.add_custom_parameter('seq.display_name', self.display_name or '')
        newrelic.agent.add_custom_parameter('seq.position', self.position)
        newrelic.agent.add_custom_parameter('seq.is_time_limited', self.is_time_limited)

    def _capture_full_seq_item_metrics(self, display_items):
        """
        Capture information about the number and types of XBlock content in
        the sequence as a whole. We send this information to New Relic so that
        we can do better performance analysis of courseware.
        """
        if not newrelic:
            return
        # Basic count of the number of Units (a.k.a. VerticalBlocks) we have in
        # this learning sequence
        newrelic.agent.add_custom_parameter('seq.num_units', len(display_items))

        # Count of all modules (leaf nodes) in this sequence (e.g. videos,
        # problems, etc.) The units (verticals) themselves are not counted.
        all_item_keys = self._locations_in_subtree(self)
        newrelic.agent.add_custom_parameter('seq.num_items', len(all_item_keys))

        # Count of all modules by block_type (e.g. "video": 2, "discussion": 4)
        block_counts = collections.Counter(usage_key.block_type for usage_key in all_item_keys)
        for block_type, count in block_counts.items():
            newrelic.agent.add_custom_parameter('seq.block_counts.{}'.format(block_type), count)

    def _capture_current_unit_metrics(self, display_items):
        """
        Capture information about the current selected Unit within the Sequence.
        """
        if not newrelic:
            return
        # Positions are stored with indexing starting at 1. If we get into a
        # weird state where the saved position is out of bounds (e.g. the
        # content was changed), avoid going into any details about this unit.
        if 1 <= self.position <= len(display_items):
            # Basic info about the Unit...
            current = display_items[self.position - 1]
            newrelic.agent.add_custom_parameter('seq.current.block_id', unicode(current.location))
            newrelic.agent.add_custom_parameter('seq.current.display_name', current.display_name or '')

            # Examining all items inside the Unit (or split_test, conditional, etc.)
            child_locs = self._locations_in_subtree(current)
            newrelic.agent.add_custom_parameter('seq.current.num_items', len(child_locs))
            curr_block_counts = collections.Counter(usage_key.block_type for usage_key in child_locs)
            for block_type, count in curr_block_counts.items():
                newrelic.agent.add_custom_parameter('seq.current.block_counts.{}'.format(block_type), count)

    def _time_limited_student_view(self):
        """
        Delegated rendering of a student view when in a time
        limited view. This ultimately calls down into edx_proctoring
        pip installed djangoapp
        """

        # None = no overridden view rendering
        view_html = None

        proctoring_service = self.runtime.service(self, 'proctoring')
        credit_service = self.runtime.service(self, 'credit')
        verification_service = self.runtime.service(self, 'verification')

        # Is this sequence designated as a Timed Examination, which includes
        # Proctored Exams
        feature_enabled = (
            proctoring_service and
            credit_service and
            self.is_time_limited
        )
        if feature_enabled:
            user_id = self.runtime.user_id
            user_role_in_course = 'staff' if self.runtime.user_is_staff else 'student'
            course_id = self.runtime.course_id
            content_id = self.location

            context = {
                'display_name': self.display_name,
                'default_time_limit_mins': (
                    self.default_time_limit_minutes if
                    self.default_time_limit_minutes else 0
                ),
                'is_practice_exam': self.is_practice_exam,
                'allow_proctoring_opt_out': self.allow_proctoring_opt_out,
                'due_date': self.due
            }

            # inject the user's credit requirements and fulfillments
            if credit_service:
                credit_state = credit_service.get_credit_state(user_id, course_id)
                if credit_state:
                    context.update({
                        'credit_state': credit_state
                    })

            # inject verification status
            if verification_service:
                verification_status, __ = verification_service.get_status(user_id)
                context.update({
                    'verification_status': verification_status,
                    'reverify_url': verification_service.reverify_url(),
                })

            # See if the edx-proctoring subsystem wants to present
            # a special view to the student rather
            # than the actual sequence content
            #
            # This will return None if there is no
            # overridden view to display given the
            # current state of the user
            view_html = proctoring_service.get_student_view(
                user_id=user_id,
                course_id=course_id,
                content_id=content_id,
                context=context,
                user_role=user_role_in_course
            )

        return view_html

    def get_icon_class(self):
        child_classes = set(child.get_icon_class()
                            for child in self.get_children())
        new_class = 'other'
        for c in class_priority:
            if c in child_classes:
                new_class = c
        return new_class


class SequenceDescriptor(SequenceFields, ProctoringFields, MakoModuleDescriptor, XmlDescriptor):
    """
    A Sequence's Descriptor object
    """
    mako_template = 'widgets/sequence-edit.html'
    module_class = SequenceModule
    resources_dir = None

    show_in_read_only_mode = True

    js = {
        'coffee': [resource_string(__name__, 'js/src/sequence/edit.coffee')],
    }
    js_module_name = "SequenceDescriptor"

    @classmethod
    def definition_from_xml(cls, xml_object, system):
        children = []
        for child in xml_object:
            try:
                child_block = system.process_xml(etree.tostring(child, encoding='unicode'))
                children.append(child_block.scope_ids.usage_id)
            except Exception as e:
                log.exception("Unable to load child when parsing Sequence. Continuing...")
                if system.error_tracker is not None:
                    system.error_tracker(u"ERROR: {0}".format(e))
                continue
        return {}, children

    def definition_to_xml(self, resource_fs):
        xml_object = etree.Element('sequential')
        for child in self.get_children():
            self.runtime.add_block_as_child_node(child, xml_object)
        return xml_object

    @property
    def non_editable_metadata_fields(self):
        """
        `is_entrance_exam` should not be editable in the Studio settings editor.
        """
        non_editable_fields = super(SequenceDescriptor, self).non_editable_metadata_fields
        non_editable_fields.append(self.fields['is_entrance_exam'])
        return non_editable_fields

    def index_dictionary(self):
        """
        Return dictionary prepared with module content and type for indexing.
        """
        # return key/value fields in a Python dict object
        # values may be numeric / string or dict
        # default implementation is an empty dict
        xblock_body = super(SequenceDescriptor, self).index_dictionary()
        html_body = {
            "display_name": self.display_name,
        }
        if "content" in xblock_body:
            xblock_body["content"].update(html_body)
        else:
            xblock_body["content"] = html_body
        xblock_body["content_type"] = "Sequence"

        return xblock_body
