"""
Module implementing `xblock.runtime.Runtime` functionality for the LMS
"""

import re
import xblock.reference.plugins

from django.core.urlresolvers import reverse
from django.conf import settings
from user_api.api import course_tag as user_course_tag_api
from xmodule.modulestore.django import modulestore
from xmodule.x_module import ModuleSystem
from xmodule.partitions.partitions_service import PartitionService


def _quote_slashes(match):
    """
    Helper function for `quote_slashes`
    """
    matched = match.group(0)
    # We have to escape ';', because that is our
    # escape sequence identifier (otherwise, the escaping)
    # couldn't distinguish between us adding ';_' to the string
    # and ';_' appearing naturally in the string
    if matched == ';':
        return ';;'
    elif matched == '/':
        return ';_'
    else:
        return matched


def quote_slashes(text):
    """
    Quote '/' characters so that they aren't visible to
    django's url quoting, unquoting, or url regex matching.

    Escapes '/'' to the sequence ';_', and ';' to the sequence
    ';;'. By making the escape sequence fixed length, and escaping
    identifier character ';', we are able to reverse the escaping.
    """
    return re.sub(ur'[;/]', _quote_slashes, text)


def _unquote_slashes(match):
    """
    Helper function for `unquote_slashes`
    """
    matched = match.group(0)
    if matched == ';;':
        return ';'
    elif matched == ';_':
        return '/'
    else:
        return matched


def unquote_slashes(text):
    """
    Unquote slashes quoted by `quote_slashes`
    """
    return re.sub(r'(;;|;_)', _unquote_slashes, text)


class LmsHandlerUrls(object):
    """
    A runtime mixin that provides a handler_url function that routes
    to the LMS' xblock handler view.

    This must be mixed in to a runtime that already accepts and stores
    a course_id
    """
    # pylint: disable=unused-argument
    # pylint: disable=no-member
    def handler_url(self, block, handler_name, suffix='', query='', thirdparty=False):
        """See :method:`xblock.runtime:Runtime.handler_url`"""
        view_name = 'xblock_handler'
        if handler_name:
            # Be sure this is really a handler.
            func = getattr(block, handler_name, None)
            if not func:
                raise ValueError("{!r} is not a function name".format(handler_name))
            if not getattr(func, "_is_xblock_handler", False):
                raise ValueError("{!r} is not a handler name".format(handler_name))

        if thirdparty:
            view_name = 'xblock_handler_noauth'

        url = reverse(view_name, kwargs={
            'course_id': self.course_id.to_deprecated_string(),
            'usage_id': quote_slashes(block.scope_ids.usage_id.to_deprecated_string().encode('utf-8')),
            'handler': handler_name,
            'suffix': suffix,
        })

        # If suffix is an empty string, remove the trailing '/'
        if not suffix:
            url = url.rstrip('/')

        # If there is a query string, append it
        if query:
            url += '?' + query

        # If third-party, return fully-qualified url
        if thirdparty:
            scheme = "https" if settings.HTTPS == "on" else "http"
            url = '{scheme}://{host}{path}'.format(
                scheme=scheme,
                host=settings.SITE_NAME,
                path=url
            )

        return url

    def local_resource_url(self, block, uri):
        """
        local_resource_url for Studio
        """
        return reverse('xblock_resource_url', kwargs={
            'block_type': block.scope_ids.block_type,
            'uri': uri,
        })


class LmsPartitionService(PartitionService):
    """
    Another runtime mixin that provides access to the student partitions defined on the
    course.

    (If and when XBlock directly provides access from one block (e.g. a split_test_module)
    to another (e.g. a course_module), this won't be neccessary, but for now it seems like
    the least messy way to hook things through)

    """
    @property
    def course_partitions(self):
        course = modulestore().get_course(self._course_id)
        return course.user_partitions


class UserTagsService(object):
    """
    A runtime class that provides an interface to the user service.  It handles filling in
    the current course id and current user.
    """

    COURSE_SCOPE = user_course_tag_api.COURSE_SCOPE

    def __init__(self, runtime):
        self.runtime = runtime

    def _get_current_user(self):
        """Returns the real, not anonymized, current user."""
        real_user = self.runtime.get_real_user(self.runtime.anonymous_student_id)
        return real_user

    def get_tag(self, scope, key):
        """
        Get a user tag for the current course and the current user for a given key

            scope: the current scope of the runtime
            key: the key for the value we want
        """
        if scope != user_course_tag_api.COURSE_SCOPE:
            raise ValueError("unexpected scope {0}".format(scope))

        return user_course_tag_api.get_course_tag(
            self._get_current_user(),
            self.runtime.course_id, key
        )

    def set_tag(self, scope, key, value):
        """
        Set the user tag for the current course and the current user for a given key

            scope: the current scope of the runtime
            key: the key that to the value to be set
            value: the value to set
        """
        if scope != user_course_tag_api.COURSE_SCOPE:
            raise ValueError("unexpected scope {0}".format(scope))

        return user_course_tag_api.set_course_tag(
            self._get_current_user(),
            self.runtime.course_id, key, value
        )


class LmsModuleSystem(LmsHandlerUrls, ModuleSystem):  # pylint: disable=abstract-method
    """
    ModuleSystem specialized to the LMS
    """
    def __init__(self, **kwargs):
        services = kwargs.setdefault('services', {})
        services['user_tags'] = UserTagsService(self)
        services['partitions'] = LmsPartitionService(
            user_tags_service=services['user_tags'],
            course_id=kwargs.get('course_id', None),
            track_function=kwargs.get('track_function', None),
        )
        services['fs'] = xblock.reference.plugins.FSService()
        super(LmsModuleSystem, self).__init__(**kwargs)
