# -*- coding: utf-8 -*-
#
# Copyright © 2012 - 2018 Michal Čihař <michal@cihar.com>
#
# This file is part of Weblate <https://weblate.org/>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
#

"""Whoosh based full text search."""

from __future__ import absolute_import, unicode_literals

import functools

from celery_batches import Batches

from whoosh.fields import SchemaClass, TEXT, NUMERIC
from whoosh.query import Or, Term
from whoosh.index import LockError
from whoosh.writing import AsyncWriter, BufferedWriter
from whoosh import qparser

from django.utils.encoding import force_text

from weblate.celery import app
from weblate.utils.celery import extract_batch_args, extract_batch_kwargs
from weblate.utils.index import WhooshIndex


class TargetSchema(SchemaClass):
    """Fultext index schema for target strings."""
    pk = NUMERIC(stored=True, unique=True)
    target = TEXT()
    comment = TEXT()


class SourceSchema(SchemaClass):
    """Fultext index schema for source and context strings."""
    pk = NUMERIC(stored=True, unique=True)
    source = TEXT()
    context = TEXT()
    location = TEXT()


class Fulltext(WhooshIndex):
    LOCATION = 'whoosh'
    FAKE = False

    def get_source_index(self):
        return self.open_index(SourceSchema, 'source')

    def get_target_index(self, lang):
        """Return target index object."""
        name = 'target-{0}'.format(lang)
        return self.open_index(TargetSchema, name)

    @staticmethod
    def update_source_unit_index(writer, unit):
        """Update source index for given unit."""
        if not isinstance(unit, dict):
            unit = {
                'source': unit.source,
                'context': unit.context,
                'location': unit.location,
                'pk': unit.pk,
            }
        writer.update_document(
            pk=unit['pk'],
            source=force_text(unit['source']),
            context=force_text(unit['context']),
            location=force_text(unit['location']),
        )

    @staticmethod
    def update_target_unit_index(writer, unit):
        """Update target index for given unit."""
        if not isinstance(unit, dict):
            unit = {
                'pk': unit.pk,
                'target': unit.target,
                'comment': unit.comment,
            }
        writer.update_document(
            pk=unit['pk'],
            target=force_text(unit['target']),
            comment=force_text(unit['comment']),
        )

    def update_index(self, units):
        """Update fulltext index for given set of units."""

        # Update source index
        index = self.get_source_index()
        with BufferedWriter(index) as writer:
            for unit in units:
                self.update_source_unit_index(writer, unit)

        languages = set([unit['language'] for unit in units])

        # Update per language indices
        for language in languages:
            index = self.get_target_index(language)
            with BufferedWriter(index) as writer:
                for unit in units:
                    if unit['language'] != language:
                        continue
                    self.update_target_unit_index(writer, unit)

    @classmethod
    def update_index_unit(cls, unit):
        """Add single unit to index."""
        if not cls.FAKE:
            update_fulltext.delay(
                pk=unit.pk,
                source=force_text(unit.source),
                context=force_text(unit.context),
                location=force_text(unit.location),
                target=force_text(unit.target),
                comment=force_text(unit.comment),
                language=force_text(unit.translation.language),
            )

    @staticmethod
    def base_search(index, query, params, search, schema):
        """Wrapper for fulltext search."""
        with index.searcher() as searcher:
            queries = []
            for param in params:
                if search[param]:
                    parser = qparser.QueryParser(param, schema)
                    queries.append(
                        parser.parse(query)
                    )
            terms = functools.reduce(lambda x, y: x | y, queries)
            return [
                result['pk'] for result in searcher.search(terms, limit=None)
            ]

    def search(self, query, langs, params):
        """Perform fulltext search in given areas.

        Returns set of primary keys.
        """
        pks = set()

        search = {
            'source': False,
            'context': False,
            'target': False,
            'comment': False,
            'location': False,
        }
        search.update(params)

        if search['source'] or search['context'] or search['location']:
            pks.update(
                self.base_search(
                    self.get_source_index(),
                    query,
                    ('source', 'context', 'location'),
                    search,
                    SourceSchema()
                )
            )

        if search['target'] or search['comment']:
            for lang in langs:
                pks.update(
                    self.base_search(
                        self.get_target_index(lang),
                        query,
                        ('target', 'comment'),
                        search,
                        TargetSchema()
                    )
                )

        return pks

    def more_like(self, pk, source, top=5):
        """Find similar units."""
        index = self.get_source_index()
        with index.searcher() as searcher:
            # Extract key terms
            kts = searcher.key_terms_from_text(
                'source', source,
                numterms=10,
                normalize=False
            )
            # Create an Or query from the key terms
            query = Or(
                [Term('source', word, boost=weight) for word, weight in kts]
            )

            # Grab fulltext results
            results = [
                (h['pk'], h.score) for h in searcher.search(query, limit=top)
            ]
            if not results:
                return []
            # Normalize scores to 0-100
            max_score = max([h[1] for h in results])
            scores = {h[0]:  h[1] * 100 / max_score for h in results}

            # Filter results with score above 50 and not current unit
            return [h[0] for h in results if scores[h[0]] > 50 and h[0] != pk]

    @classmethod
    def clean_search_unit(cls, pk, lang):
        """Cleanup search index on unit deletion."""
        if not cls.FAKE:
            delete_fulltext.delay(pk, lang)

    def delete_search_unit(self, pk, lang):
        try:
            indexes = (
                self.get_source_index(),
                self.get_target_index(lang)
            )
            for index in indexes:
                with AsyncWriter(index) as writer:
                    writer.delete_by_term('pk', pk)
        except IOError:
            return

    def delete_search_units(self, source_units, languages):
        """Delete fulltext index for given set of units."""
        # Update source index
        index = self.get_source_index()
        with index.writer() as writer:
            for pk in source_units:
                writer.delete_by_term('pk', pk)

        for lang, units in languages.items():
            index = self.get_target_index(lang)
            with index.writer() as writer:
                for pk in units:
                    writer.delete_by_term('pk', pk)


@app.task(
    base=Batches, flush_every=1000, flush_interval=300, bind=True,
    max_retries=1000
)
def update_fulltext(self, *args, **kwargs):
    unitdata = extract_batch_kwargs(*args, **kwargs)
    fulltext = Fulltext()

    # Update index
    try:
        fulltext.update_index(unitdata)
    except LockError as exc:
        raise self.retry(exc=exc)


@app.task(
    base=Batches, flush_every=1000, flush_interval=300, bind=True,
    max_retries=1000
)
def delete_fulltext(self, *args):
    ids = extract_batch_args(*args)
    fulltext = Fulltext()

    units = set()
    languages = {}
    for unit, language in ids:
        units.add(unit)
        if language is None:
            continue
        if language not in languages:
            languages[language] = set()
        languages[language].add(unit)

    try:
        fulltext.delete_search_units(units, languages)
    except LockError as exc:
        raise self.retry(exc=exc)
