# -*- coding: utf-8 -*-
# sync.py
# Copyright (C) 2014 LEAP
#
# 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 <http://www.gnu.org/licenses/>.
"""
Soledad synchronization utilities.
"""
import logging

from twisted.internet import defer

from u1db import errors
from leap.soledad.common.errors import MissingDesignDocError
from u1db.sync import Synchronizer


logger = logging.getLogger(__name__)


class SoledadSynchronizer(Synchronizer):
    """
    Collect the state around synchronizing 2 U1DB replicas.

    Synchronization is bi-directional, in that new items in the source are sent
    to the target, and new items in the target are returned to the source.
    However, it still recognizes that one side is initiating the request. Also,
    at the moment, conflicts are only created in the source.

    Also modified to allow for interrupting the synchronization process.
    """
    received_docs = []

    @defer.inlineCallbacks
    def sync(self, defer_decryption=True):
        """
        Synchronize documents between source and target.

        Differently from u1db `Synchronizer.sync` method, this one allows to
        pass a `defer_decryption` flag that will postpone the last
        step in the synchronization dance, namely, the setting of the last
        known generation and transaction id for a given remote replica.

        This is done to allow the ongoing parallel decryption of the incoming
        docs to proceed without `InvalidGeneration` conflicts.

        :param defer_decryption: Whether to defer the decryption process using
                                 the intermediate database. If False,
                                 decryption will be done inline.
        :type defer_decryption: bool

        :return: A deferred which will fire after the sync has finished with
                 the local generation before the synchronization was performed.
        :rtype: twisted.internet.defer.Deferred
        """
        sync_target = self.sync_target
        self.received_docs = []

        # get target identifier, its current generation,
        # and its last-seen database generation for this source
        ensure_callback = None
        try:
            (self.target_replica_uid, target_gen, target_trans_id,
             target_my_gen, target_my_trans_id) = yield \
                sync_target.get_sync_info(self.source._replica_uid)
        except (errors.DatabaseDoesNotExist, MissingDesignDocError) as e:
            logger.debug("Database isn't ready on server. Will be created.")
            logger.debug("Reason: %s", e.__class__)
            self.target_replica_uid = None
            target_gen, target_trans_id = 0, ''
            target_my_gen, target_my_trans_id = 0, ''

        logger.debug(
            "Soledad target sync info:\n"
            "  target replica uid: %s\n"
            "  target generation: %d\n"
            "  target trans id: %s\n"
            "  target my gen: %d\n"
            "  target my trans_id: %s\n"
            "  source replica_uid: %s\n"
            % (self.target_replica_uid, target_gen, target_trans_id,
               target_my_gen, target_my_trans_id, self.source._replica_uid))

        # make sure we'll have access to target replica uid once it exists
        if self.target_replica_uid is None:

            def ensure_callback(replica_uid):
                self.target_replica_uid = replica_uid

        # make sure we're not syncing one replica with itself
        if self.target_replica_uid == self.source._replica_uid:
            raise errors.InvalidReplicaUID

        # validate the info the target has about the source replica
        self.source.validate_gen_and_trans_id(
            target_my_gen, target_my_trans_id)

        # what's changed since that generation and this current gen
        my_gen, _, changes = self.source.whats_changed(target_my_gen)
        logger.debug("Soledad sync: there are %d documents to send."
                     % len(changes))

        # get source last-seen database generation for the target
        if self.target_replica_uid is None:
            target_last_known_gen, target_last_known_trans_id = 0, ''
        else:
            target_last_known_gen, target_last_known_trans_id = \
                self.source._get_replica_gen_and_trans_id(
                    self.target_replica_uid)
        logger.debug(
            "Soledad source sync info:\n"
            "  last target gen known to source: %d\n"
            "  last target trans_id known to source: %s"
            % (target_last_known_gen, target_last_known_trans_id))

        # validate transaction ids
        if not changes and target_last_known_gen == target_gen:
            if target_trans_id != target_last_known_trans_id:
                raise errors.InvalidTransactionId
            defer.returnValue(my_gen)

        # prepare to send all the changed docs
        changed_doc_ids = [doc_id for doc_id, _, _ in changes]
        docs_to_send = self.source.get_docs(
            changed_doc_ids, check_for_conflicts=False, include_deleted=True)
        ids_sent = []
        docs_by_generation = []
        idx = 0
        for doc in docs_to_send:
            _, gen, trans = changes[idx]
            docs_by_generation.append((doc, gen, trans))
            idx += 1
            ids_sent.append(doc.doc_id)

        # exchange documents and try to insert the returned ones with
        # the target, return target synced-up-to gen.
        new_gen, new_trans_id = yield sync_target.sync_exchange(
            docs_by_generation, self.source._replica_uid,
            target_last_known_gen, target_last_known_trans_id,
            self._insert_doc_from_target, ensure_callback=ensure_callback,
            defer_decryption=defer_decryption)
        logger.debug(
            "Soledad source sync info after sync exchange:\n"
            "  source known target gen: %d\n"
            "  source known target trans_id: %s"
            % (new_gen, new_trans_id))
        info = {
            "target_replica_uid": self.target_replica_uid,
            "new_gen": new_gen,
            "new_trans_id": new_trans_id,
            "my_gen": my_gen
        }
        self._syncing_info = info
        yield self.complete_sync()

        _, _, changes = self.source.whats_changed(target_my_gen)
        changed_doc_ids = [doc_id for doc_id, _, _ in changes]

        just_received = list(set(changed_doc_ids) - set(ids_sent))
        self.received_docs = just_received

        defer.returnValue(my_gen)

    def complete_sync(self):
        """
        Last stage of the synchronization:
            (a) record last known generation and transaction uid for the remote
            replica, and
            (b) make target aware of our current reached generation.

        :return: A deferred which will fire when the sync has been completed.
        :rtype: twisted.internet.defer.Deferred
        """
        logger.debug("Completing deferred last step in SYNC...")

        # record target synced-up-to generation including applying what we
        # sent
        info = self._syncing_info
        self.source._set_replica_gen_and_trans_id(
            info["target_replica_uid"], info["new_gen"], info["new_trans_id"])

        # if gapless record current reached generation with target
        return self._record_sync_info_with_the_target(info["my_gen"])

    def close(self):
        """
        Close the synchronizer.
        """
        self.sync_target.close()

    def _record_sync_info_with_the_target(self, start_generation):
        """
        Store local replica metadata in server.

        :param start_generation: The local generation when the sync was
                                 started.
        :type start_generation: int

        :return: A deferred which will fire when the operation has been
                 completed.
        :rtype: twisted.internet.defer.Deferred
        """
        cur_gen, trans_id = self.source._get_generation_info()
        if (cur_gen == start_generation + self.num_inserted and
                self.num_inserted > 0):
            return self.sync_target.record_sync_info(
                self.source._replica_uid, cur_gen, trans_id)
        return defer.succeed(None)
