# coding=utf-8
"""
Indexing service for Abilian.

Adds Whoosh indexing capabilities to SQLAlchemy models.

Based on Flask-whooshalchemy by Karl Gyllstrom.

:copyright: (c) 2013-2014 by Abilian SAS
:copyright: (c) 2012 by Stefane Fermigier
:copyright: (c) 2012 by Karl Gyllstrom
:license: BSD (see LICENSE.txt)
"""
from __future__ import absolute_import, division, print_function

import logging
import os
from inspect import isclass

import sqlalchemy as sa
import whoosh.index
import whoosh.query as wq
from celery import shared_task
from flask import _app_ctx_stack, appcontext_pushed, current_app, g
from flask.globals import _lookup_app_object
from flask_login import current_user
from sqlalchemy import event
from sqlalchemy.orm.session import Session
from whoosh.analysis import CharsetFilter, StemmingAnalyzer
from whoosh.collectors import WrappingCollector
from whoosh.filedb.filestore import FileStorage, RamStorage
from whoosh.qparser import DisMaxParser
from whoosh.support.charset import accent_map
from whoosh.writing import CLEAR, AsyncWriter

from abilian.core import signals
from abilian.core.celery import safe_session
from abilian.core.entities import Entity, Indexable
from abilian.core.extensions import db
from abilian.core.models.subjects import Group, User
from abilian.core.util import fqcn as base_fqcn
from abilian.core.util import friendly_fqcn
from abilian.services import Service, ServiceState
from abilian.services.security import Anonymous, Authenticated, Role, security

from .adapter import SAAdapter
from .schema import DefaultSearchSchema, indexable_role

logger = logging.getLogger(__name__)
_TEXT_ANALYZER = StemmingAnalyzer() | CharsetFilter(accent_map)

_pending_indexation_attr = 'abilian_pending_indexation'

# as of whoosh 2.5.7, a method is missing on WrappingCollector. See
# https://bitbucket.org/mchaput/whoosh/issue/394/error-when-searching-with-groupedby-and
_PATCHED = False

if not _PATCHED:

    def wrapping_collector_remove(self, global_docnum):
        return self.child.remove(global_docnum)

    from abilian.core.logging import patch_logger
    patch_logger.info(WrappingCollector.remove)
    WrappingCollector.remove = wrapping_collector_remove
    _PATCHED = True
    del patch_logger
    del wrapping_collector_remove
# END PATCH


def url_for_hit(hit, default=u'#'):
    """
    Helper for building URLs from results
    """
    try:
        object_type = hit['object_type']
        object_id = int(hit['id'])
        return current_app.default_view.url_for(hit, object_type, object_id)
    except KeyError:
        return default
    except Exception:
        logger.error('Error building URL for search result', exc_info=True)
        return default


def fqcn(cls):
    if issubclass(cls, Entity):
        return cls.entity_type
    return base_fqcn(cls)


class IndexServiceState(ServiceState):
    whoosh_base = None
    indexes = None
    indexed_classes = None
    indexed_fqcn = None
    search_filter_funcs = None
    value_provider_funcs = None
    url_for_hit = None

    def __init__(self, *args, **kwargs):
        ServiceState.__init__(self, *args, **kwargs)
        self.indexes = {}
        self.indexed_classes = set()
        self.indexed_fqcn = set()
        self.search_filter_funcs = []
        self.value_provider_funcs = []
        self.url_for_hit = url_for_hit

    @property
    def to_update(self):
        return _lookup_app_object(_pending_indexation_attr)

    @to_update.setter
    def to_update(self, value):
        top = _app_ctx_stack.top
        if top is None:
            raise RuntimeError('working outside of application context')

        setattr(top, _pending_indexation_attr, value)


class WhooshIndexService(Service):
    """
    Index documents using whoosh
    """
    name = 'indexing'
    AppStateClass = IndexServiceState

    _listening = False

    def __init__(self, *args, **kwargs):
        Service.__init__(self, *args, **kwargs)
        self.adapters_cls = [SAAdapter]
        self.adapted = {}
        self.schemas = {'default': DefaultSearchSchema()}

    def init_app(self, app):
        Service.init_app(self, app)
        state = app.extensions[self.name]

        whoosh_base = app.config.get("WHOOSH_BASE")
        if not whoosh_base:
            whoosh_base = "whoosh"  # Default value

        if not os.path.isabs(whoosh_base):
            whoosh_base = os.path.join(app.instance_path, whoosh_base)

        state.whoosh_base = os.path.abspath(whoosh_base)

        if not self._listening:
            event.listen(Session, "after_flush", self.after_flush)
            event.listen(Session, "after_commit", self.after_commit)
            self._listening = True

        appcontext_pushed.connect(self.clear_update_queue, app)
        signals.register_js_api.connect(self._do_register_js_api)

    def _do_register_js_api(self, sender):
        app = sender
        js_api = app.js_api.setdefault('search', {})
        js_api['object_types'] = self.searchable_object_types()

    def register_search_filter(self, func):
        """
        Register a function that returns a query used for filtering search
        results. This query is And'ed with other filters.

        If no filtering should be performed the function must return None.
        """
        self.app_state.search_filter_funcs.append(func)

    def register_value_provider(self, func):
        """Register a function that may alter content of indexable document.

        It is used in :meth:`get_document` and called after adapter has built
        document.

        The function must accept (document, obj) as arguments, and return
        the new document object.
        """
        self.app_state.value_provider_funcs.append(func)

    def clear_update_queue(self, app=None):
        self.app_state.to_update = []

    def start(self):
        Service.start(self)
        self.register_classes()
        self.init_indexes()
        self.clear_update_queue()

    def init_indexes(self):
        """Create indexes for schemas.
        """
        state = self.app_state

        for name, schema in self.schemas.iteritems():
            if current_app.testing:
                storage = TestingStorage()
            else:
                index_path = os.path.join(state.whoosh_base, name)
                if not os.path.exists(index_path):
                    os.makedirs(index_path)
                storage = FileStorage(index_path)

            FileIndex = whoosh.index.FileIndex
            if not storage.index_exists(name):
                FileIndex = whoosh.index.FileIndex.create

            index = FileIndex(storage, schema, name)
            state.indexes[name] = index

    def clear(self):
        """Remove all content from indexes, and unregister all classes.

        After clear() the service is stopped. It must be started again to create
        new indexes and register classes.
        """
        logger.info('Resetting indexes')
        state = self.app_state

        for name, idx in state.indexes.iteritems():
            writer = AsyncWriter(idx)
            writer.commit(merge=True, optimize=True, mergetype=CLEAR)

        state.indexes = {}
        state.indexed_classes = set()
        state.indexed_fqcn = set()
        self.clear_update_queue()

        if self.running:
            self.stop()

    def index(self, name='default'):
        return self.app_state.indexes[name]

    @property
    def default_search_fields(self):
        """
        Return default field names and boosts to be used for searching. Can be
        configured with `SEARCH_DEFAULT_BOOSTS`
        """
        config = current_app.config.get('SEARCH_DEFAULT_BOOSTS')
        if not config:
            config = dict(name=1.5, name_prefix=1.3, description=1.3, text=1.0,)
            return config

    def searchable_object_types(self):
        """
        List of (object_types, friendly name) present in the index.
        """
        try:
            idx = self.index()
        except KeyError:
            # index does not exists: service never started, may happens during tests
            return []

        with idx.reader() as r:
            indexed = sorted(set(r.field_terms('object_type')))
        app_indexed = self.app_state.indexed_fqcn

        return [(name, friendly_fqcn(name))
                for name in indexed if name in app_indexed]

    def search(self,
               q,
               index='default',
               fields=None,
               Models=(),
               object_types=(),
               prefix=True,
               facet_by_type=None,
               **search_args):
        """Interface to search indexes.

        :param q: unparsed search string.
        :param index: name of index to use for search.
        :param fields: optionnal mapping of field names -> boost factor?
        :param Models: list of Model classes to limit search on.
        :param object_types: same as `Models`, but directly the model string.
        :param prefix: enable or disable search by prefix
        :param facet_by_type: if set, returns a dict of object_type: results with a
             max of `limit` matches for each type.
        :param search_args: any valid parameter for
            :meth:`whoosh.searching.Search.search`. This includes `limit`,
            `groupedby` and `sortedby`
        """
        index = self.app_state.indexes[index]
        if not fields:
            fields = self.default_search_fields

        valid_fields = set(f
                           for f in index.schema.names(check_names=fields)
                           if prefix or not f.endswith('_prefix'))

        for invalid in set(fields) - valid_fields:
            del fields[invalid]

        parser = DisMaxParser(fields, index.schema)
        query = parser.parse(q)

        filters = search_args.setdefault('filter', None)
        filters = [filters] if filters is not None else []
        del search_args['filter']

        if not hasattr(g, 'is_manager') or not g.is_manager:
            # security access filter
            user = current_user
            roles = {indexable_role(user)}
            if not user.is_anonymous():
                roles.add(indexable_role(Anonymous))
                roles.add(indexable_role(Authenticated))
                roles |= set(indexable_role(r)
                             for r in security.get_roles(user))

            filter_q = wq.Or([wq.Term('allowed_roles_and_users', role)
                              for role in roles])
            filters.append(filter_q)

        object_types = set(object_types)
        for m in Models:
            object_type = m.entity_type
            if not object_type:
                continue
            object_types.add(object_type)

        if object_types:
            object_types &= self.app_state.indexed_fqcn
        else:
            # ensure we don't show content types previously indexed but not yet
            # cleaned from index
            object_types = self.app_state.indexed_fqcn

        # limit object_type
        filter_q = wq.Or([wq.Term('object_type', t) for t in object_types])
        filters.append(filter_q)

        for func in self.app_state.search_filter_funcs:
            filter_q = func()
            if filter_q is not None:
                filters.append(filter_q)

        if filters:
            filter_q = wq.And(filters) if len(filters) > 1 else filters[0]
            #search_args['filter'] = filter_q
            query = filter_q & query

        if facet_by_type:
            if not object_types:
                object_types = [t[0] for t in self.searchable_object_types()]

            # limit number of documents to score, per object type
            collapse_limit = 5
            search_args['groupedby'] = 'object_type'
            search_args['collapse'] = 'object_type'
            search_args['collapse_limit'] = collapse_limit
            search_args['limit'] = (search_args['collapse_limit'] * max(
                len(object_types), 1))

        with index.searcher(closereader=False) as searcher:
            # 'closereader' is needed, else results cannot by used outside 'with'
            # statement
            results = searcher.search(query, **search_args)

            if facet_by_type:
                positions = {
                    doc_id: pos
                    for pos, doc_id in enumerate(i[1] for i in results.top_n)
                }
                sr = results
                results = {}
                for typename, doc_ids in sr.groups('object_type').items():
                    results[typename] = [sr[positions[oid]]
                                         for oid in doc_ids[:collapse_limit]]

            return results

    def search_for_class(self, query, cls, index='default', **search_args):
        return self.search(
            query, Models=(fqcn(cls),),
            index=index, **search_args)

    def register_classes(self):
        state = self.app_state
        classes = (cls
                   for cls in db.Model._decl_class_registry.values()
                   if isclass(cls) and issubclass(cls, Indexable) and
                   cls.__indexable__)
        for cls in classes:
            if cls not in state.indexed_classes:
                self.register_class(cls, app_state=state)

    def register_class(self, cls, app_state=None):
        """
        Registers a model class
        """
        state = app_state if app_state is not None else self.app_state

        for Adapter in self.adapters_cls:
            if Adapter.can_adapt(cls):
                break
        else:
            return

        cls_fqcn = fqcn(cls)
        self.adapted[cls_fqcn] = Adapter(cls, self.schemas['default'])
        state.indexed_classes.add(cls)
        state.indexed_fqcn.add(cls_fqcn)

    def after_flush(self, session, flush_context):
        if not self.running or session is not db.session():
            return

        to_update = self.app_state.to_update
        session_objs = (('new', session.new),
                        ('deleted', session.deleted),
                        ('changed', session.dirty),)
        for key, objs in session_objs:
            for obj in objs:
                model_name = fqcn(obj.__class__)
                adapter = self.adapted.get(model_name)

                if adapter is None or not adapter.indexable:
                    continue

                to_update.append((key, obj))

    def after_commit(self, session):
        """
        Any db updates go through here. We check if any of these models have
        ``__searchable__`` fields, indicating they need to be indexed. With these
        we update the whoosh index for the model. If no index exists, it will be
        created here; this could impose a penalty on the initial commit of a model.
        """
        if (not self.running or
                session.transaction.nested  # inside a sub-transaction:
                # not yet written in DB
                or session is not db.session()):
            # note: we have not tested too far if session is enclosed in a transaction
            # at connection level. For now it's not a standard use case, it would most
            # likely happens during tests (which don't do that for now)
            return

        primary_field = 'id'
        state = self.app_state
        items = []
        for op, obj in state.to_update:
            model_name = fqcn(obj.__class__)
            if model_name not in self.adapted or \
                    not self.adapted[model_name].indexable:
                # safeguard
                continue

            # safeguard against DetachedInstanceError
            if sa.orm.object_session(obj) is not None:
                items.append((op, model_name, getattr(obj, primary_field), {}))

        if items:
            index_update.apply_async(kwargs=dict(index='default', items=items))
        self.clear_update_queue()

    def get_document(self, obj, adapter=None):
        if adapter is None:
            class_name = fqcn(obj.__class__)
            adapter = self.adapted.get(class_name)

        if adapter is None or not adapter.indexable:
            return None

        document = adapter.get_document(obj)

        for k, v in document.items():
            if v is None:
                del document[k]
                continue
            if isinstance(v, (User, Group, Role)):
                document[k] = indexable_role(v)

        if not document.get('allowed_roles_and_users'):
            # no data for security: assume anybody can access the document
            document['allowed_roles_and_users'] = indexable_role(Anonymous)

        for func in self.app_state.value_provider_funcs:
            res = func(document, obj)
            if res is not None:
                document = res

        return document

    def index_objects(self, objects, index='default'):
        """Bulk index a list of objects.
        """
        if not objects:
            return

        index_name = index
        index = self.app_state.indexes[index_name]
        indexed = set()

        with index.writer() as writer:
            for obj in objects:
                document = self.get_document(obj)
                if document is None:
                    continue

                object_key = document['object_key']
                if object_key in indexed:
                    continue

                writer.delete_by_term('object_key', object_key)
                try:
                    writer.add_document(**document)
                except ValueError:
                    # logger is here to give us more infos in order to catch a weird bug
                    # that happens regularly on CI but is not reliably reproductible.
                    logger.error('writer.add_document(%r)',
                                 document,
                                 exc_info=True)
                    raise
                indexed.add(object_key)


service = WhooshIndexService()


@shared_task
def index_update(index, items):
    """
    :param:index: index name
    :param:items: list of (operation, full class name, primary key, data) tuples.
    """
    index_name = index
    index = service.app_state.indexes[index_name]
    adapted = service.adapted

    session = safe_session()
    updated = set()
    writer = AsyncWriter(index)
    try:
        for op, cls_name, pk, data in items:
            if pk is None:
                continue

            # always delete. Whoosh manual says that 'update' is actually delete + add
            # operation
            object_key = u'{}:{}'.format(cls_name, pk)
            writer.delete_by_term('object_key', object_key)

            adapter = adapted.get(cls_name)
            if not adapter:
                # FIXME: log to sentry?
                continue

            if object_key in updated:
                # don't add twice the same document in same transaction. The writer will
                # not delete previous records, ending in duplicate records for same
                # document.
                continue

            if op in ("new", "changed"):
                with session.begin(nested=True):
                    obj = adapter.retrieve(pk, _session=session, **data)

                if obj is None:
                    # deleted after task queued, but before task run
                    continue

                document = service.get_document(obj, adapter)
                try:
                    writer.add_document(**document)
                except ValueError:
                    # logger is here to give us more infos in order to catch a weird bug
                    # that happens regularly on CI but is not reliably reproductible.
                    logger.error('writer.add_document(%r)',
                                 document,
                                 exc_info=True)
                    raise
                updated.add(object_key)
    except:
        writer.cancel()
        raise

    session.close()
    writer.commit()
    try:
        # async thread: wait for its termination
        writer.join()
    except RuntimeError:
        # happens when actual writer was already available: asyncwriter didn't need
        # to start a thread
        pass


class TestingStorage(RamStorage):
    """
    RamStorage whoses temp_storage method returns another TestingStorage
    instead of a FileStorage.

    Reason is that FileStorage.temp_storage() creates temp file in

    /tmp/index_name.tmp/, which is subject to race conditions when many
    tests are ran in parallel, including different abilian-based packages.
    """

    def temp_storage(self, name=None):
        return TestingStorage()
