"""
Functions that can are used to modify XBlock fragments for use in the LMS and Studio
"""

import datetime
import json
import logging
import markupsafe
import re
import static_replace
import uuid
from lxml import html, etree
from contracts import contract

from django.conf import settings
from django.contrib.staticfiles.storage import staticfiles_storage
from django.core.urlresolvers import reverse
from pytz import UTC
from django.utils.html import escape
from django.contrib.auth.models import User
from edxmako.shortcuts import render_to_string
from xblock.core import XBlock
from xblock.exceptions import InvalidScopeError
from xblock.fragment import Fragment
from xblock.scorable import ScorableXBlockMixin

from xmodule.seq_module import SequenceModule
from xmodule.vertical_block import VerticalBlock
from xmodule.x_module import shim_xmodule_js, XModuleDescriptor, XModule, PREVIEW_VIEWS, STUDIO_VIEW

log = logging.getLogger(__name__)


def wrap_fragment(fragment, new_content):
    """
    Returns a new Fragment that has `new_content` and all
    as its content, and all of the resources from fragment
    """
    wrapper_frag = Fragment(content=new_content)
    wrapper_frag.add_frag_resources(fragment)
    return wrapper_frag


def request_token(request):
    """
    Return a unique token for the supplied request.
    This token will be the same for all calls to `request_token`
    made on the same request object.
    """
    # pylint: disable=protected-access
    if not hasattr(request, '_xblock_token'):
        request._xblock_token = uuid.uuid1().get_hex()

    return request._xblock_token


def wrap_xblock(
        runtime_class,
        block,
        view,
        frag,
        context,                        # pylint: disable=unused-argument
        usage_id_serializer,
        request_token,                  # pylint: disable=redefined-outer-name
        display_name_only=False,
        extra_data=None
):
    """
    Wraps the results of rendering an XBlock view in a standard <section> with identifying
    data so that the appropriate javascript module can be loaded onto it.

    :param runtime_class: The name of the javascript runtime class to use to load this block
    :param block: An XBlock (that may be an XModule or XModuleDescriptor)
    :param view: The name of the view that rendered the fragment being wrapped
    :param frag: The :class:`Fragment` to be wrapped
    :param context: The context passed to the view being rendered
    :param usage_id_serializer: A function to serialize the block's usage_id for use by the
        front-end Javascript Runtime.
    :param request_token: An identifier that is unique per-request, so that only xblocks
        rendered as part of this request will have their javascript initialized.
    :param display_name_only: If true, don't render the fragment content at all.
        Instead, just render the `display_name` of `block`
    :param extra_data: A dictionary with extra data values to be set on the wrapper
    """
    if extra_data is None:
        extra_data = {}

    # If any mixins have been applied, then use the unmixed class
    class_name = getattr(block, 'unmixed_class', block.__class__).__name__

    data = {}
    data.update(extra_data)

    css_classes = [
        'xblock',
        'xblock-{}'.format(markupsafe.escape(view)),
        'xblock-{}-{}'.format(
            markupsafe.escape(view),
            markupsafe.escape(block.scope_ids.block_type),
        )
    ]

    if isinstance(block, (XModule, XModuleDescriptor)):
        if view in PREVIEW_VIEWS:
            # The block is acting as an XModule
            css_classes.append('xmodule_display')
        elif view == STUDIO_VIEW:
            # The block is acting as an XModuleDescriptor
            css_classes.append('xmodule_edit')

        if getattr(block, 'HIDDEN', False):
            css_classes.append('is-hidden')

        css_classes.append('xmodule_' + markupsafe.escape(class_name))
        data['type'] = block.js_module_name
        shim_xmodule_js(block, frag)

    if frag.js_init_fn:
        data['init'] = frag.js_init_fn
        data['runtime-class'] = runtime_class
        data['runtime-version'] = frag.js_init_version

    data['block-type'] = block.scope_ids.block_type
    data['usage-id'] = usage_id_serializer(block.scope_ids.usage_id)
    data['request-token'] = request_token

    if block.name:
        data['name'] = block.name

    template_context = {
        'content': block.display_name if display_name_only else frag.content,
        'classes': css_classes,
        'display_name': block.display_name_with_default_escaped,
        'data_attributes': u' '.join(u'data-{}="{}"'.format(markupsafe.escape(key), markupsafe.escape(value))
                                     for key, value in data.iteritems()),
    }

    if hasattr(frag, 'json_init_args') and frag.json_init_args is not None:
        # Replace / with \/ so that "</script>" in the data won't break things.
        template_context['js_init_parameters'] = json.dumps(frag.json_init_args).replace("/", r"\/")
    else:
        template_context['js_init_parameters'] = ""

    return wrap_fragment(frag, render_to_string('xblock_wrapper.html', template_context))


def wrap_xblock_aside(
        runtime_class,
        aside,
        view,
        frag,
        context,                        # pylint: disable=unused-argument
        usage_id_serializer,
        request_token,                   # pylint: disable=redefined-outer-name
        extra_data=None
):
    """
    Wraps the results of rendering an XBlockAside view in a standard <section> with identifying
    data so that the appropriate javascript module can be loaded onto it.

    :param runtime_class: The name of the javascript runtime class to use to load this block
    :param aside: An XBlockAside
    :param view: The name of the view that rendered the fragment being wrapped
    :param frag: The :class:`Fragment` to be wrapped
    :param context: The context passed to the view being rendered
    :param usage_id_serializer: A function to serialize the block's usage_id for use by the
        front-end Javascript Runtime.
    :param request_token: An identifier that is unique per-request, so that only xblocks
        rendered as part of this request will have their javascript initialized.
    :param extra_data: A dictionary with extra data values to be set on the wrapper
    """

    if extra_data is None:
        extra_data = {}

    data = {}
    data.update(extra_data)

    css_classes = [
        'xblock-{}'.format(markupsafe.escape(view)),
        'xblock-{}-{}'.format(
            markupsafe.escape(view),
            markupsafe.escape(aside.scope_ids.block_type),
        ),
        'xblock_asides-v1'
    ]

    if frag.js_init_fn:
        data['init'] = frag.js_init_fn
        data['runtime-class'] = runtime_class
        data['runtime-version'] = frag.js_init_version

    data['block-type'] = aside.scope_ids.block_type
    data['usage-id'] = usage_id_serializer(aside.scope_ids.usage_id)
    data['request-token'] = request_token

    template_context = {
        'content': frag.content,
        'classes': css_classes,
        'data_attributes': u' '.join(u'data-{}="{}"'.format(markupsafe.escape(key), markupsafe.escape(value))
                                     for key, value in data.iteritems()),
    }

    if hasattr(frag, 'json_init_args') and frag.json_init_args is not None:
        # Replace / with \/ so that "</script>" in the data won't break things.
        template_context['js_init_parameters'] = json.dumps(frag.json_init_args).replace("/", r"\/")
    else:
        template_context['js_init_parameters'] = ""

    return wrap_fragment(frag, render_to_string('xblock_wrapper.html', template_context))


def replace_jump_to_id_urls(course_id, jump_to_id_base_url, block, view, frag, context):  # pylint: disable=unused-argument
    """
    This will replace a link between courseware in the format
    /jump_to_id/<id> with a URL for a page that will correctly redirect
    This is similar to replace_course_urls, but much more flexible and
    durable for Studio authored courses. See more comments in static_replace.replace_jump_to_urls

    course_id: The course_id in which this rewrite happens
    jump_to_id_base_url:
        A app-tier (e.g. LMS) absolute path to the base of the handler that will perform the
        redirect. e.g. /courses/<org>/<course>/<run>/jump_to_id. NOTE the <id> will be appended to
        the end of this URL at re-write time

    output: a new :class:`~xblock.fragment.Fragment` that modifies `frag` with
        content that has been update with /jump_to_id links replaced
    """
    return wrap_fragment(frag, static_replace.replace_jump_to_id_urls(frag.content, course_id, jump_to_id_base_url))


def replace_course_urls(course_id, block, view, frag, context):  # pylint: disable=unused-argument
    """
    Updates the supplied module with a new get_html function that wraps
    the old get_html function and substitutes urls of the form /course/...
    with urls that are /courses/<course_id>/...
    """
    return wrap_fragment(frag, static_replace.replace_course_urls(frag.content, course_id))


def replace_static_urls(data_dir, block, view, frag, context, course_id=None, static_asset_path=''):  # pylint: disable=unused-argument
    """
    Updates the supplied module with a new get_html function that wraps
    the old get_html function and substitutes urls of the form /static/...
    with urls that are /static/<prefix>/...
    """
    return wrap_fragment(frag, static_replace.replace_static_urls(
        frag.content,
        data_dir,
        course_id,
        static_asset_path=static_asset_path
    ))


def grade_histogram(module_id):
    '''
    Print out a histogram of grades on a given problem in staff member debug info.

    Warning: If a student has just looked at an xmodule and not attempted
    it, their grade is None. Since there will always be at least one such student
    this function almost always returns [].
    '''
    from django.db import connection
    cursor = connection.cursor()

    query = """\
        SELECT courseware_studentmodule.grade,
        COUNT(courseware_studentmodule.student_id)
        FROM courseware_studentmodule
        WHERE courseware_studentmodule.module_id=%s
        GROUP BY courseware_studentmodule.grade"""
    # Passing module_id this way prevents sql-injection.
    cursor.execute(query, [module_id.to_deprecated_string()])

    grades = list(cursor.fetchall())
    grades.sort(key=lambda x: x[0])  # Add ORDER BY to sql query?
    if len(grades) >= 1 and grades[0][0] is None:
        return []
    return grades


def sanitize_html_id(html_id):
    """
    Template uses element_id in js function names, so can't allow dashes and colons.
    """
    sanitized_html_id = re.sub(r'[:-]', '_', html_id)
    return sanitized_html_id


@contract(user=User, has_instructor_access=bool, block=XBlock, view=basestring, frag=Fragment, context="dict|None")
def add_staff_markup(user, has_instructor_access, disable_staff_debug_info, block, view, frag, context):  # pylint: disable=unused-argument
    """
    Updates the supplied module with a new get_html function that wraps
    the output of the old get_html function with additional information
    for admin users only, including a histogram of student answers, the
    definition of the xmodule, and a link to view the module in Studio
    if it is a Studio edited, mongo stored course.

    Does nothing if module is a SequenceModule.
    """
    # TODO: make this more general, eg use an XModule attribute instead
    if isinstance(block, VerticalBlock) and (not context or not context.get('child_of_vertical', False)):
        # check that the course is a mongo backed Studio course before doing work
        is_studio_course = block.course_edit_method == "Studio"

        if is_studio_course:
            # build edit link to unit in CMS. Can't use reverse here as lms doesn't load cms's urls.py
            edit_link = "//" + settings.CMS_BASE + '/container/' + unicode(block.location)

            # return edit link in rendered HTML for display
            return wrap_fragment(
                frag,
                render_to_string(
                    "edit_unit_link.html",
                    {'frag_content': frag.content, 'edit_link': edit_link}
                )
            )
        else:
            return frag

    if isinstance(block, SequenceModule) or getattr(block, 'HIDDEN', False):
        return frag

    block_id = block.location
    if block.has_score and settings.FEATURES.get('DISPLAY_HISTOGRAMS_TO_STAFF'):
        histogram = grade_histogram(block_id)
        render_histogram = len(histogram) > 0
    else:
        histogram = None
        render_histogram = False

    if settings.FEATURES.get('ENABLE_LMS_MIGRATION') and hasattr(block.runtime, 'filestore'):
        [filepath, filename] = getattr(block, 'xml_attributes', {}).get('filename', ['', None])
        osfs = block.runtime.filestore
        if filename is not None and osfs.exists(filename):
            # if original, unmangled filename exists then use it (github
            # doesn't like symlinks)
            filepath = filename
        data_dir = block.static_asset_path or osfs.root_path.rsplit('/')[-1]
        giturl = block.giturl or 'https://github.com/MITx'
        edit_link = "%s/%s/tree/master/%s" % (giturl, data_dir, filepath)
    else:
        edit_link = False
        # Need to define all the variables that are about to be used
        giturl = ""
        data_dir = ""

    source_file = block.source_file  # source used to generate the problem XML, eg latex or word

    # Useful to indicate to staff if problem has been released or not.
    # TODO (ichuang): use _has_access_descriptor.can_load in lms.courseware.access,
    # instead of now>mstart comparison here.
    now = datetime.datetime.now(UTC)
    is_released = "unknown"
    mstart = block.start

    if mstart is not None:
        is_released = "<font color='red'>Yes!</font>" if (now > mstart) else "<font color='green'>Not yet</font>"

    field_contents = []
    for name, field in block.fields.items():
        try:
            field_contents.append((name, field.read_from(block)))
        except InvalidScopeError:
            log.warning("Unable to read field in Staff Debug information", exc_info=True)
            field_contents.append((name, "WARNING: Unable to read field"))

    staff_context = {
        'fields': field_contents,
        'xml_attributes': getattr(block, 'xml_attributes', {}),
        'tags': block._class_tags,  # pylint: disable=protected-access
        'location': block.location,
        'xqa_key': block.xqa_key,
        'source_file': source_file,
        'source_url': '%s/%s/tree/master/%s' % (giturl, data_dir, source_file),
        'category': str(block.__class__.__name__),
        'element_id': sanitize_html_id(block.location.html_id()),
        'edit_link': edit_link,
        'user': user,
        'xqa_server': settings.FEATURES.get('XQA_SERVER', "http://your_xqa_server.com"),
        'histogram': json.dumps(histogram),
        'render_histogram': render_histogram,
        'block_content': frag.content,
        'is_released': is_released,
        'has_instructor_access': has_instructor_access,
        'can_reset_attempts': 'attempts' in block.fields,
        'can_rescore_problem': hasattr(block, 'rescore'),
        'can_override_problem_score': isinstance(block, ScorableXBlockMixin),
        'disable_staff_debug_info': disable_staff_debug_info,
    }
    if isinstance(block, ScorableXBlockMixin):
        staff_context['max_problem_score'] = block.max_score()

    return wrap_fragment(frag, render_to_string("staff_problem_info.html", staff_context))


def get_course_update_items(course_updates, provided_index=0):
    """
    Returns list of course_updates data dictionaries either from new format if available or
    from old. This function don't modify old data to new data (in db), instead returns data
    in common old dictionary format.
    New Format: {"items" : [{"id": computed_id, "date": date, "content": html-string}],
                 "data": "<ol>[<li><h2>date</h2>content</li>]</ol>"}
    Old Format: {"data": "<ol>[<li><h2>date</h2>content</li>]</ol>"}
    """
    def _course_info_content(html_parsed):
        """
        Constructs the HTML for the course info update, not including the header.
        """
        if len(html_parsed) == 1:
            # could enforce that update[0].tag == 'h2'
            content = html_parsed[0].tail
        else:
            content = html_parsed[0].tail if html_parsed[0].tail is not None else ""
            content += "\n".join([html.tostring(ele) for ele in html_parsed[1:]])
        return content

    if course_updates and getattr(course_updates, "items", None):
        if provided_index and 0 < provided_index <= len(course_updates.items):
            return course_updates.items[provided_index - 1]
        else:
            # return list in reversed order (old format: [4,3,2,1]) for compatibility
            return list(reversed(course_updates.items))

    course_update_items = []
    if course_updates:
        # old method to get course updates
        # purely to handle free formed updates not done via editor. Actually kills them, but at least doesn't break.
        try:
            course_html_parsed = html.fromstring(course_updates.data)
        except (etree.XMLSyntaxError, etree.ParserError):
            log.error("Cannot parse: " + course_updates.data)
            escaped = escape(course_updates.data)
            course_html_parsed = html.fromstring("<ol><li>" + escaped + "</li></ol>")

        # confirm that root is <ol>, iterate over <li>, pull out <h2> subs and then rest of val
        if course_html_parsed.tag == 'ol':
            # 0 is the newest
            for index, update in enumerate(course_html_parsed):
                if len(update) > 0:
                    content = _course_info_content(update)
                    # make the id on the client be 1..len w/ 1 being the oldest and len being the newest
                    computed_id = len(course_html_parsed) - index
                    payload = {
                        "id": computed_id,
                        "date": update.findtext("h2"),
                        "content": content
                    }
                    if provided_index == 0:
                        course_update_items.append(payload)
                    elif provided_index == computed_id:
                        return payload

    return course_update_items


def xblock_local_resource_url(block, uri):
    """
    Returns the URL for an XBlock's local resource.

    Note: when running with the full Django pipeline, the file will be accessed
    as a static asset which will use a CDN in production.
    """
    xblock_class = getattr(block.__class__, 'unmixed_class', block.__class__)
    if settings.PIPELINE_ENABLED or not settings.REQUIRE_DEBUG:
        return staticfiles_storage.url('xblock/resources/{package_name}/{path}'.format(
            package_name=xblock_class.__module__,
            path=uri
        ))
    else:
        return reverse('xblock_resource_url', kwargs={
            'block_type': block.scope_ids.block_type,
            'uri': uri,
        })
