# Copyright 2013-2014 MongoDB, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Tails the oplog of a shard and returns entries
"""

import bson
import logging
try:
    import Queue as queue
except ImportError:
    import queue
import pymongo
import sys
import time
import threading
import traceback
from mongo_connector import errors, util
from mongo_connector.constants import DEFAULT_BATCH_SIZE
from mongo_connector.util import retry_until_ok

from pymongo import MongoClient


class OplogThread(threading.Thread):
    """OplogThread gathers the updates for a single oplog.
    """
    def __init__(self, primary_conn, main_address, oplog_coll, is_sharded,
                 doc_manager, oplog_progress_dict, namespace_set, auth_key,
                 auth_username, repl_set=None, collection_dump=True,
                 batch_size=DEFAULT_BATCH_SIZE, fields=None,
                 dest_mapping={}, continue_on_error=False):
        """Initialize the oplog thread.
        """
        super(OplogThread, self).__init__()

        self.batch_size = batch_size

        #The connection to the primary for this replicaSet.
        self.primary_connection = primary_conn

        #Boolean chooses whether to dump the entire collection if no timestamp
        # is present in the config file
        self.collection_dump = collection_dump

        #The mongos for sharded setups
        #Otherwise the same as primary_connection.
        #The value is set later on.
        self.main_connection = None

        #The connection to the oplog collection
        self.oplog = oplog_coll

        #Boolean describing whether the cluster is sharded or not
        self.is_sharded = is_sharded

        #A document manager for each target system.
        #These are the same for all threads.
        if type(doc_manager) == list:
            self.doc_managers = doc_manager
        else:
            self.doc_managers = [doc_manager]

        #Boolean describing whether or not the thread is running.
        self.running = True

        #Stores the timestamp of the last oplog entry read.
        self.checkpoint = None

        #A dictionary that stores OplogThread/timestamp pairs.
        #Represents the last checkpoint for a OplogThread.
        self.oplog_progress = oplog_progress_dict

        #The set of namespaces to process from the mongo cluster.
        self.namespace_set = namespace_set

        #The dict of source namespaces to destination namespaces
        self.dest_mapping = dest_mapping

        #Whether the collection dump gracefully handles exceptions
        self.continue_on_error = continue_on_error

        #If authentication is used, this is an admin password.
        self.auth_key = auth_key

        #This is the username used for authentication.
        self.auth_username = auth_username

        # Set of fields to export
        self.fields = fields

        logging.info('OplogThread: Initializing oplog thread')

        if is_sharded:
            self.main_connection = MongoClient(
                main_address, tz_aware=primary_conn.tz_aware)
        else:
            self.main_connection = MongoClient(
                main_address, replicaSet=repl_set,
                tz_aware=primary_conn.tz_aware)
            self.oplog = self.main_connection['local']['oplog.rs']

        if auth_key is not None:
            #Authenticate for the whole system
            self.primary_connection['admin'].authenticate(
                auth_username, auth_key)
            self.main_connection['admin'].authenticate(
                auth_username, auth_key)
        if not self.oplog.find_one():
            err_msg = 'OplogThread: No oplog for thread:'
            logging.warning('%s %s' % (err_msg, self.primary_connection))

    @property
    def fields(self):
        return self._fields

    @fields.setter
    def fields(self, value):
        if value:
            self._fields = set(value)
            # Always include _id field
            self._fields.add('_id')
        else:
            self._fields = None

    def run(self):
        """Start the oplog worker.
        """
        logging.debug("OplogThread: Run thread started")
        while self.running is True:
            logging.debug("OplogThread: Getting cursor")
            cursor, cursor_len = self.init_cursor()

            # we've fallen too far behind
            if cursor is None and self.checkpoint is not None:
                err_msg = "OplogThread: Last entry no longer in oplog"
                effect = "cannot recover!"
                logging.error('%s %s %s' % (err_msg, effect, self.oplog))
                self.running = False
                continue

            if cursor_len == 0:
                logging.debug("OplogThread: Last entry is the one we "
                              "already processed.  Up to date.  Sleeping.")
                time.sleep(1)
                continue

            logging.debug("OplogThread: Got the cursor, count is %d"
                          % cursor_len)

            last_ts = None
            err = False
            remove_inc = 0
            upsert_inc = 0
            update_inc = 0
            try:
                logging.debug("OplogThread: about to process new oplog "
                              "entries")
                while cursor.alive and self.running:
                    logging.debug("OplogThread: Cursor is still"
                                  " alive and thread is still running.")
                    for n, entry in enumerate(cursor):

                        logging.debug("OplogThread: Iterating through cursor,"
                                      " document number in this cursor is %d"
                                      % n)
                        # Break out if this thread should stop
                        if not self.running:
                            break

                        # Don't replicate entries resulting from chunk moves
                        if entry.get("fromMigrate"):
                            continue

                        # Take fields out of the oplog entry that
                        # shouldn't be replicated. This may nullify
                        # the document if there's nothing to do.
                        if not self.filter_oplog_entry(entry):
                            continue

                        #sync the current oplog operation
                        operation = entry['op']
                        ns = entry['ns']

                        if '.' not in ns:
                            continue

                        coll = ns.split('.', 1)[1]
                        if coll.startswith("system."):
                            continue

                        # use namespace mapping if one exists
                        ns = self.dest_mapping.get(entry['ns'], ns)

                        for docman in self.doc_managers:
                            try:
                                logging.debug("OplogThread: Operation for this "
                                              "entry is %s" % str(operation))

                                # Remove
                                if operation == 'd':
                                    entry['_id'] = entry['o']['_id']
                                    entry['ns'] = ns
                                    entry['_ts'] = util.bson_ts_to_long(
                                        entry['ts'])
                                    docman.remove(entry)
                                    remove_inc += 1
                                # Insert
                                elif operation == 'i':  # Insert
                                    # Retrieve inserted document from
                                    # 'o' field in oplog record
                                    doc = entry.get('o')
                                    # Extract timestamp and namespace
                                    doc['_ts'] = util.bson_ts_to_long(
                                        entry['ts'])
                                    doc['ns'] = ns
                                    docman.upsert(doc)
                                    upsert_inc += 1
                                # Update
                                elif operation == 'u':
                                    doc = {"_id": entry['o2']['_id'],
                                           "_ts": util.bson_ts_to_long(
                                               entry['ts']),
                                           "ns": ns}
                                    # 'o' field contains the update spec
                                    docman.update(doc, entry.get('o', {}))
                                    update_inc += 1
                            except errors.OperationFailed:
                                logging.exception(
                                    "Unable to process oplog document %r"
                                    % entry)
                            except errors.ConnectionFailed:
                                logging.exception(
                                    "Connection failed while processing oplog "
                                    "document %r" % entry)

                        if (remove_inc + upsert_inc + update_inc) % 1000 == 0:
                            logging.debug(
                                "OplogThread: Documents removed: %d, "
                                "inserted: %d, updated: %d so far" % (
                                    remove_inc, upsert_inc, update_inc))

                        logging.debug("OplogThread: Doc is processed.")

                        last_ts = entry['ts']

                        # update timestamp per batch size
                        # n % -1 (default for self.batch_size) == 0 for all n
                        if n % self.batch_size == 1 and last_ts is not None:
                            self.checkpoint = last_ts
                            self.update_checkpoint()

                    # update timestamp after running through oplog
                    if last_ts is not None:
                        logging.debug("OplogThread: updating checkpoint after"
                                      "processing new oplog entries")
                        self.checkpoint = last_ts
                        self.update_checkpoint()

            except (pymongo.errors.AutoReconnect,
                    pymongo.errors.OperationFailure,
                    pymongo.errors.ConfigurationError):
                logging.exception(
                    "Cursor closed due to an exception. "
                    "Will attempt to reconnect.")
                err = True

            if err is True and self.auth_key is not None:
                self.primary_connection['admin'].authenticate(
                    self.auth_username, self.auth_key)
                self.main_connection['admin'].authenticate(
                    self.auth_username, self.auth_key)
                err = False

            # update timestamp before attempting to reconnect to MongoDB,
            # after being join()'ed, or if the cursor closes
            if last_ts is not None:
                logging.debug("OplogThread: updating checkpoint after an "
                              "Exception, cursor closing, or join() on this"
                              "thread.")
                self.checkpoint = last_ts
                self.update_checkpoint()

            logging.debug("OplogThread: Sleeping. Documents removed: %d, "
                          "upserted: %d, updated: %d"
                          % (remove_inc, upsert_inc, update_inc))
            time.sleep(2)

    def join(self):
        """Stop this thread from managing the oplog.
        """
        logging.debug("OplogThread: exiting due to join call.")
        self.running = False
        threading.Thread.join(self)

    def filter_oplog_entry(self, entry):
        """Remove fields from an oplog entry that should not be replicated."""
        if not self._fields:
            return entry

        def pop_excluded_fields(doc):
            for key in set(doc) - self._fields:
                doc.pop(key)

        # 'i' indicates an insert. 'o' field is the doc to be inserted.
        if entry['op'] == 'i':
            pop_excluded_fields(entry['o'])
        # 'u' indicates an update. 'o' field is the update spec.
        elif entry['op'] == 'u':
            pop_excluded_fields(entry['o'].get("$set", {}))
            pop_excluded_fields(entry['o'].get("$unset", {}))
            # not allowed to have empty $set/$unset, so remove if empty
            if "$set" in entry['o'] and not entry['o']['$set']:
                entry['o'].pop("$set")
            if "$unset" in entry['o'] and not entry['o']['$unset']:
                entry['o'].pop("$unset")
            if not entry['o']:
                return None

        return entry

    def get_oplog_cursor(self, timestamp=None):
        """Get a cursor to the oplog after the given timestamp, filtering
        entries not in the namespace set.
        If no timestamp is specified, returns a cursor to the entire oplog.
        """
        query = {}
        if self.namespace_set:
            query['ns'] = {'$in': self.namespace_set}

        if timestamp is None:
            cursor = self.oplog.find(
                query,
                tailable=True, await_data=True, timeout=False)
        else:
            query['ts'] = {'$gte': timestamp}
            cursor = self.oplog.find(
                query, tailable=True, await_data=True, timeout=False)
            # Applying 8 as the mask to the cursor enables OplogReplay
            cursor.add_option(8)

        return cursor

    def dump_collection(self):
        """Dumps collection into the target system.

        This method is called when we're initializing the cursor and have no
        configs i.e. when we're starting for the first time.
        """

        dump_set = self.namespace_set or []
        logging.debug("OplogThread: Dumping set of collections %s " % dump_set)

        #no namespaces specified
        if not self.namespace_set:
            db_list = retry_until_ok(self.main_connection.database_names)
            for database in db_list:
                if database == "config" or database == "local":
                    continue
                coll_list = retry_until_ok(
                    self.main_connection[database].collection_names)
                for coll in coll_list:
                    if coll.startswith("system"):
                        continue
                    namespace = "%s.%s" % (database, coll)
                    dump_set.append(namespace)

        timestamp = util.retry_until_ok(self.get_last_oplog_timestamp)
        if timestamp is None:
            return None
        long_ts = util.bson_ts_to_long(timestamp)

        def docs_to_dump():
            for namespace in dump_set:
                logging.info("OplogThread: dumping collection %s"
                             % namespace)
                database, coll = namespace.split('.', 1)
                last_id = None
                attempts = 0

                # Loop to handle possible AutoReconnect
                while attempts < 60:
                    target_coll = self.main_connection[database][coll]
                    find_kwargs = {
                        'fields': self._fields,
                        'sort': [('_id', pymongo.ASCENDING)],
                        'timeout': False
                    }
                    if not self.is_sharded:
                        find_kwargs['exhaust'] = True
                    if not last_id:
                        cursor = util.retry_until_ok(
                            target_coll.find, **find_kwargs)
                    else:
                        cursor = util.retry_until_ok(
                            target_coll.find,
                            {"_id": {"$gt": last_id}},
                            **find_kwargs
                        )
                    try:
                        for doc in cursor:
                            if not self.running:
                                raise StopIteration
                            doc["ns"] = self.dest_mapping.get(
                                namespace, namespace)
                            doc["_ts"] = long_ts
                            last_id = doc["_id"]
                            yield doc
                        break
                    except (pymongo.errors.AutoReconnect,
                            pymongo.errors.OperationFailure):
                        attempts += 1
                        time.sleep(1)

        def upsert_each(dm):
            num_inserted = 0
            num_failed = 0
            for num, doc in enumerate(docs_to_dump()):
                if num % 10000 == 0:
                    logging.debug("Upserted %d docs." % num)
                try:
                    dm.upsert(doc)
                    num_inserted += 1
                except Exception:
                    if self.continue_on_error:
                        logging.exception(
                            "Could not upsert document: %r" % doc)
                        num_failed += 1
                    else:
                        raise
            logging.debug("Upserted %d docs" % num_inserted)
            if num_failed > 0:
                logging.error("Failed to upsert %d docs" % num_failed)

        def upsert_all(dm):
            try:
                dm.bulk_upsert(docs_to_dump())
            except Exception as e:
                if self.continue_on_error:
                    logging.exception("OplogThread: caught exception"
                                      " during bulk upsert, re-upserting"
                                      " documents serially")
                    upsert_each(dm)
                else:
                    raise

        def do_dump(dm, error_queue):
            try:
                # Bulk upsert if possible
                if hasattr(dm, "bulk_upsert"):
                    logging.debug("OplogThread: Using bulk upsert function for "
                                  "collection dump")
                    upsert_all(dm)
                else:
                    logging.debug(
                        "OplogThread: DocManager %s has no "
                        "bulk_upsert method.  Upserting documents "
                        "serially for collection dump." % str(dm))
                    upsert_each(dm)
            except:
                # Likely exceptions:
                # pymongo.errors.OperationFailure,
                # mongo_connector.errors.ConnectionFailed
                # mongo_connector.errors.OperationFailed
                error_queue.put(sys.exc_info())


        # Extra threads (if any) that assist with collection dumps
        dumping_threads = []
        # Did the dump succeed for all target systems?
        dump_success = True
        # Holds any exceptions we can't recover from
        errors = queue.Queue()

        if len(self.doc_managers) == 1:
            do_dump(self.doc_managers[0], errors)
        else:
            # Slight performance gain breaking dump into separate
            # threads if > 1 replication target
            for dm in self.doc_managers:
                t = threading.Thread(target=do_dump, args=(dm, errors))
                dumping_threads.append(t)
                t.start()
            # cleanup
            for t in dumping_threads:
                t.join()

        # Print caught exceptions
        try:
            while True:
                klass, value, trace = errors.get_nowait()
                dump_success = False
                traceback.print_exception(klass, value, trace)
        except queue.Empty:
            pass

        if not dump_success:
            err_msg = "OplogThread: Failed during dump collection"
            effect = "cannot recover!"
            logging.error('%s %s %s' % (err_msg, effect, self.oplog))
            self.running = False
            return None

        return timestamp

    def get_last_oplog_timestamp(self):
        """Return the timestamp of the latest entry in the oplog.
        """
        if not self.namespace_set:
            curr = self.oplog.find().sort(
                '$natural', pymongo.DESCENDING
            ).limit(1)
        else:
            curr = self.oplog.find(
                {'ns': {'$in': self.namespace_set}}
            ).sort('$natural', pymongo.DESCENDING).limit(1)

        if curr.count(with_limit_and_skip=True) == 0:
            return None

        logging.debug("OplogThread: Last oplog entry has timestamp %d."
                      % curr[0]['ts'].time)
        return curr[0]['ts']

    def init_cursor(self):
        """Position the cursor appropriately.

        The cursor is set to either the beginning of the oplog, or
        wherever it was last left off.

        Returns the cursor and the number of documents left in the cursor.
        """
        timestamp = self.read_last_checkpoint()

        if timestamp is None:
            if self.collection_dump:
                # dump collection and update checkpoint
                timestamp = self.dump_collection()
                if timestamp is None:
                    return None, 0
            else:
                # Collection dump disabled:
                # return cursor to beginning of oplog.
                cursor = self.get_oplog_cursor()
                self.checkpoint = self.get_last_oplog_timestamp()
                self.update_checkpoint()
                return cursor, retry_until_ok(cursor.count)

        self.checkpoint = timestamp
        self.update_checkpoint()

        for i in range(60):
            cursor = self.get_oplog_cursor(timestamp)
            cursor_len = retry_until_ok(cursor.count)

            if cursor_len == 0:
                # rollback, update checkpoint, and retry
                logging.debug("OplogThread: Initiating rollback from "
                              "get_oplog_cursor")
                self.checkpoint = self.rollback()
                self.update_checkpoint()
                return self.init_cursor()

            # try to get the first oplog entry
            try:
                first_oplog_entry = retry_until_ok(next, cursor)
            except StopIteration:
                # It's possible for the cursor to become invalid
                # between the cursor.count() call and now
                time.sleep(1)
                continue

            # first entry should be last oplog entry processed
            cursor_ts_long = util.bson_ts_to_long(
                first_oplog_entry.get("ts"))
            given_ts_long = util.bson_ts_to_long(timestamp)
            if cursor_ts_long > given_ts_long:
                # first entry in oplog is beyond timestamp
                # we've fallen behind
                return None, 0

            # first entry has been consumed
            return cursor, cursor_len - 1

        else:
            raise errors.MongoConnectorError(
                "Could not initialize oplog cursor.")

    def update_checkpoint(self):
        """Store the current checkpoint in the oplog progress dictionary.
        """
        with self.oplog_progress as oplog_prog:
            oplog_dict = oplog_prog.get_dict()
            oplog_dict[str(self.oplog)] = self.checkpoint
            logging.debug("OplogThread: oplog checkpoint updated to %s" %
                          str(self.checkpoint))

    def read_last_checkpoint(self):
        """Read the last checkpoint from the oplog progress dictionary.
        """
        oplog_str = str(self.oplog)
        ret_val = None

        with self.oplog_progress as oplog_prog:
            oplog_dict = oplog_prog.get_dict()
            if oplog_str in oplog_dict.keys():
                ret_val = oplog_dict[oplog_str]

        logging.debug("OplogThread: reading last checkpoint as %s " %
                      str(ret_val))
        return ret_val

    def rollback(self):
        """Rollback target system to consistent state.

        The strategy is to find the latest timestamp in the target system and
        the largest timestamp in the oplog less than the latest target system
        timestamp. This defines the rollback window and we just roll these
        back until the oplog and target system are in consistent states.
        """
        # Find the most recently inserted document in each target system
        logging.debug("OplogThread: Initiating rollback sequence to bring "
                      "system into a consistent state.")
        last_docs = []
        for dm in self.doc_managers:
            dm.commit()
            last_docs.append(dm.get_last_doc())

        # Of these documents, which is the most recent?
        last_inserted_doc = max(last_docs,
                                key=lambda x: x["_ts"] if x else float("-inf"))

        # Nothing has been replicated. No need to rollback target systems
        if last_inserted_doc is None:
            return None

        # Find the oplog entry that touched the most recent document.
        # We'll use this to figure where to pick up the oplog later.
        target_ts = util.long_to_bson_ts(last_inserted_doc['_ts'])
        last_oplog_entry = util.retry_until_ok(
            self.oplog.find_one,
            {'ts': {'$lte': target_ts}},
            sort=[('$natural', pymongo.DESCENDING)]
        )

        logging.debug("OplogThread: last oplog entry is %s"
                      % str(last_oplog_entry))

        # The oplog entry for the most recent document doesn't exist anymore.
        # If we've fallen behind in the oplog, this will be caught later
        if last_oplog_entry is None:
            return None

        # rollback_cutoff_ts happened *before* the rollback
        rollback_cutoff_ts = last_oplog_entry['ts']
        start_ts = util.bson_ts_to_long(rollback_cutoff_ts)
        # timestamp of the most recent document on any target system
        end_ts = last_inserted_doc['_ts']

        for dm in self.doc_managers:
            rollback_set = {}   # this is a dictionary of ns:list of docs

            # group potentially conflicted documents by namespace
            for doc in dm.search(start_ts, end_ts):
                if doc['ns'] in rollback_set:
                    rollback_set[doc['ns']].append(doc)
                else:
                    rollback_set[doc['ns']] = [doc]

            # retrieve these documents from MongoDB, either updating
            # or removing them in each target system
            for namespace, doc_list in rollback_set.items():
                # Get the original namespace
                original_namespace = namespace
                for source_name, dest_name in self.dest_mapping.items():
                    if dest_name == namespace:
                        original_namespace = source_name

                database, coll = original_namespace.split('.', 1)
                obj_id = bson.objectid.ObjectId
                bson_obj_id_list = [obj_id(doc['_id']) for doc in doc_list]

                find_kwargs = {
                    'fields': self._fields,
                    'timeout': False
                }
                if not self.is_sharded:
                    find_kwargs['exhaust'] = True
                to_update = util.retry_until_ok(
                    self.main_connection[database][coll].find,
                    {'_id': {'$in': bson_obj_id_list}},
                    **find_kwargs
                )
                #doc list are docs in target system, to_update are
                #docs in mongo
                doc_hash = {}  # hash by _id
                for doc in doc_list:
                    doc_hash[bson.objectid.ObjectId(doc['_id'])] = doc

                to_index = []

                def collect_existing_docs():
                    for doc in to_update:
                        if doc['_id'] in doc_hash:
                            del doc_hash[doc['_id']]
                            to_index.append(doc)
                retry_until_ok(collect_existing_docs)

                #delete the inconsistent documents
                logging.debug("OplogThread: Rollback, removing inconsistent "
                              "docs.")
                remov_inc = 0
                for doc in doc_hash.values():
                    try:
                        dm.remove(doc)
                        remov_inc += 1
                        logging.debug(
                            "OplogThread: Rollback, removed %r " % doc)
                    except errors.OperationFailed:
                        logging.warning(
                            "Could not delete document during rollback: %r "
                            "This can happen if this document was already "
                            "removed by another rollback happening at the "
                            "same time." % doc
                        )

                logging.debug("OplogThread: Rollback, removed %d docs." %
                              remov_inc)

                #insert the ones from mongo
                logging.debug("OplogThread: Rollback, inserting documents "
                              "from mongo.")
                insert_inc = 0
                fail_insert_inc = 0
                for doc in to_index:
                    doc['_ts'] = util.bson_ts_to_long(rollback_cutoff_ts)
                    doc['ns'] = self.dest_mapping.get(namespace, namespace)
                    try:
                        insert_inc += 1
                        dm.upsert(doc)
                    except errors.OperationFailed:
                        fail_insert_inc += 1
                        logging.exception("OplogThread: Rollback, Unable to "
                                          "insert %r" % doc)

        logging.debug("OplogThread: Rollback, Successfully inserted %d "
                      " documents and failed to insert %d"
                      " documents.  Returning a rollback cutoff time of %s "
                      % (insert_inc, fail_insert_inc, str(rollback_cutoff_ts)))

        return rollback_cutoff_ts
