#
# Copyright (C) 2012-2019  Nexedi SA
#
# 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 2
# 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/>.

from collections import OrderedDict
import os
import sqlite3
from hashlib import sha1
import string
import traceback

from . import LOG_QUERIES
from .manager import DatabaseManager, splitOIDField
from neo.lib import logging, util
from neo.lib.interfaces import implements
from neo.lib.protocol import ZERO_OID, ZERO_TID, ZERO_HASH

def unique_constraint_message(table, *columns):
    c = sqlite3.connect(":memory:")
    values = '?' * len(columns)
    insert = "INSERT INTO %s VALUES(%s)" % (table, ', '.join(values))
    x = "%s (%s)" % (table, ', '.join(columns))
    c.execute("CREATE TABLE " + x)
    c.execute("CREATE UNIQUE INDEX i ON " + x)
    try:
        c.executemany(insert, (values, values))
    except sqlite3.IntegrityError, e:
        return e.args[0]
    assert False

def retry_if_locked(f, *args):
    try:
        return f(*args)
    except sqlite3.OperationalError as e:
        x = e.args[0]
        if x != 'database is locked':
            raise
        msg = traceback.format_exception_only(type(e), e)
        msg += traceback.format_stack()
        logging.warning(''.join(msg))
        while 1:
            try:
                return f(*args)
            except sqlite3.OperationalError as e:
                if e.args[0] != x:
                    raise


@implements
class SQLiteDatabaseManager(DatabaseManager):
    """This class manages a database on SQLite.

    CAUTION: Make sure we never use statement journal files, as explained at
             https://www.sqlite.org/tempfiles.html for more information.
             In other words, temporary files (by default in /var/tmp !) must
             never be used for small requests.
    """

    VERSION = 3

    def _parse(self, database):
        self.db = os.path.expanduser(database)

    def _close(self):
        self.conn.close()

    def _connect(self):
        logging.info('connecting to SQLite database %r', self.db)
        self.conn = sqlite3.connect(self.db, check_same_thread=False)
        self.conn.text_factory = str
        self.lock(self.db)
        if self.UNSAFE:
            q = self.query
            q("PRAGMA synchronous = OFF")
            q("PRAGMA journal_mode = MEMORY")
        self._config = {}

    def _getDevPath(self):
        return self.db

    def _commit(self):
        retry_if_locked(self.conn.commit)

    if LOG_QUERIES:
        def query(self, query):
            printable_char_list = []
            for c in query.split('\n', 1)[0][:70]:
                if c not in string.printable or c in '\t\x0b\x0c\r':
                    c = '\\x%02x' % ord(c)
                printable_char_list.append(c)
            logging.debug('querying %s...', ''.join(printable_char_list))
            return self.conn.execute(query)
    else:
        query = property(lambda self: self.conn.execute)

    def erase(self):
        for t in 'config', 'pt', 'trans', 'obj', 'data', 'ttrans', 'tobj':
            self.query('DROP TABLE IF EXISTS ' + t)

    def nonempty(self, table):
        try:
            return bool(self.query(
                "SELECT 1 FROM %s LIMIT 1" % table).fetchone())
        except sqlite3.OperationalError as e:
            if not e.args[0].startswith("no such table:"):
                raise

    def _alterTable(self, schema_dict, table, select="*"):
        # BBB: As explained in _setup, no transactional DDL
        #      so let's do the same dance as for MySQL.
        q = self.query
        new = 'new_' + table
        if self.nonempty(table) is None:
            if self.nonempty(new) is None:
                return
        else:
            q("DROP TABLE IF EXISTS " + new)
            q(schema_dict.pop(table) % new)
            q("INSERT INTO %s SELECT %s FROM %s" % (new, select, table))
            q("DROP TABLE " + table)
        q("ALTER TABLE %s RENAME TO %s" % (new, table))

    def _migrate1(self, *_):
        self._checkNoUnfinishedTransactions()
        self.query("DROP TABLE IF EXISTS ttrans")

    def _migrate2(self, schema_dict, index_dict):
        self._alterTable(schema_dict, 'obj')

    def _migrate3(self, schema_dict, index_dict):
        self._alterTable(schema_dict, 'pt', "rid, nid, CASE state"
            " WHEN 0 THEN -1"  # UP_TO_DATE
            " WHEN 2 THEN -2"  # FEEDING
            " ELSE 1-state END")

    # Let's wait for a more important change to clean up,
    # so that users can still downgrade.
    if 0:
      def _migrate4(self, schema_dict, index_dict):
        self._setConfiguration('partitions', None)

    def _setup(self, dedup=False):
        # BBB: SQLite has transactional DDL but before Python 3.6,
        #      the binding automatically commits between such statements.
        #      This anti-feature causes this method to be relatively slow.
        #      Unit tests enables the UNSAFE boolean flag.
        self._config.clear()
        q = self.query
        schema_dict = OrderedDict()
        index_dict = {}

        # The table "config" stores configuration
        # parameters which affect the persistent data.
        schema_dict['config'] = """CREATE TABLE %s (
                 name TEXT NOT NULL PRIMARY KEY,
                 value TEXT)
            """

        # The table "pt" stores a partition table.
        schema_dict['pt'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 nid INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 PRIMARY KEY (partition, nid))
            """

        # The table "trans" stores information on committed transactions.
        schema_dict['trans'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 packed BOOLEAN NOT NULL,
                 oids BLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid INTEGER NOT NULL,
                 PRIMARY KEY (partition, tid)
            ) WITHOUT ROWID
            """

        # The table "obj" stores committed object metadata.
        schema_dict['obj'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 oid INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 data_id INTEGER,
                 value_tid INTEGER,
                 PRIMARY KEY (partition, oid, tid)
            ) WITHOUT ROWID
            """
        index_dict['obj'] = (
            "CREATE INDEX %s ON %s(partition, tid, oid)",
            "CREATE INDEX %s ON %s(data_id)")

        # The table "data" stores object data.
        schema_dict['data'] = """CREATE TABLE %s (
                 id INTEGER PRIMARY KEY,
                 hash BLOB NOT NULL,
                 compression INTEGER NOT NULL,
                 value BLOB NOT NULL)
            """
        if dedup:
            index_dict['data'] = (
                "CREATE UNIQUE INDEX %s ON %s(hash, compression)",)

        # The table "ttrans" stores information on uncommitted transactions.
        schema_dict['ttrans'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 tid INTEGER,
                 packed BOOLEAN NOT NULL,
                 oids BLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid INTEGER NOT NULL)
            """

        # The table "tobj" stores uncommitted object metadata.
        schema_dict['tobj'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 oid INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 data_id INTEGER,
                 value_tid INTEGER,
                 PRIMARY KEY (tid, oid))
            """

        if self.nonempty('config') is None:
            q(schema_dict.pop('config') % 'config')
            self._setConfiguration('version', self.VERSION)
        else:
            self.migrate(schema_dict, index_dict)

        for table, schema in schema_dict.iteritems():
            q(schema % ('IF NOT EXISTS ' + table))
        for table, index in index_dict.iteritems():
            for i, index in enumerate(index, 1):
                q(index % ('IF NOT EXISTS _%s_i%s' % (table, i), table))

        self._uncommitted_data.update(q("SELECT data_id, count(*)"
            " FROM tobj WHERE data_id IS NOT NULL GROUP BY data_id"))

    def getConfiguration(self, key):
        try:
            return self._config[key]
        except KeyError:
            try:
                r = self.query("SELECT value FROM config WHERE name=?",
                               (key,)).fetchone()[0]
            except TypeError:
                r = None
            self._config[key] = r
            return r

    def _setConfiguration(self, key, value):
        q = self.query
        self._config[key] = value
        if value is None:
            q("DELETE FROM config WHERE name=?", (key,))
        else:
            q("REPLACE INTO config VALUES (?,?)", (key, str(value)))

    def _getMaxPartition(self):
        return self.query("SELECT MAX(`partition`) FROM pt").next()[0]

    def _getPartitionTable(self):
        return self.query("SELECT * FROM pt")

    def _getLastTID(self, partition, max_tid=None):
        x = self.query
        if max_tid is None:
            x = x("SELECT MAX(tid) FROM trans WHERE partition=?", (partition,))
        else:
            x = x("SELECT MAX(tid) FROM trans WHERE partition=? AND tid<=?",
                  (partition, max_tid))
        return x.next()[0]

    def _getLastIDs(self, *args):
        q = self.query
        (oid,), = q("SELECT MAX(oid) FROM obj WHERE `partition`=?", args)
        (tid,), = q("SELECT MAX(tid) FROM obj WHERE `partition`=?", args)
        return tid, oid

    def _getDataLastId(self, partition):
        return self.query("SELECT MAX(id) FROM data WHERE %s <= id AND id < %s"
            % (partition << 48, (partition + 1) << 48)).fetchone()[0]

    def _getUnfinishedTIDDict(self):
        q = self.query
        return q("SELECT ttid, tid FROM ttrans"), (ttid
            for ttid, in q("SELECT DISTINCT tid FROM tobj"))

    def getFinalTID(self, ttid):
        ttid = util.u64(ttid)
        # As of SQLite 3.8.7.1, 'tid>=ttid' would ignore the index on tid,
        # even though ttid is a constant.
        for tid, in self.query("SELECT tid FROM trans"
                " WHERE partition=? AND tid>=? AND ttid=? LIMIT 1",
                (self._getReadablePartition(ttid), ttid, ttid)):
            return util.p64(tid)

    def getLastObjectTID(self, oid):
        oid = util.u64(oid)
        r = self.query("SELECT tid FROM obj"
                       " WHERE partition=? AND oid=?"
                       " ORDER BY tid DESC LIMIT 1",
                       (self._getReadablePartition(oid), oid)).fetchone()
        return r and util.p64(r[0])

    def _getNextTID(self, *args): # partition, oid, tid
        r = self.query("""SELECT tid FROM obj
                          WHERE partition=? AND oid=? AND tid>?
                          ORDER BY tid LIMIT 1""", args).fetchone()
        return r and r[0]

    def _getObject(self, oid, tid=None, before_tid=None):
        q = self.query
        partition = self._getReadablePartition(oid)
        sql = ('SELECT tid, compression, data.hash, value, value_tid'
               ' FROM obj LEFT JOIN data ON obj.data_id = data.id'
               ' WHERE partition=? AND oid=?')
        if tid is not None:
            r = q(sql + ' AND tid=?', (partition, oid, tid))
        elif before_tid is not None:
            r = q(sql + ' AND tid<? ORDER BY tid DESC LIMIT 1',
                  (partition, oid, before_tid))
        else:
            r = q(sql + ' ORDER BY tid DESC LIMIT 1', (partition, oid))
        try:
            serial, compression, checksum, data, value_serial = r.fetchone()
        except TypeError:
            return None
        if checksum:
            checksum = str(checksum)
            data = str(data)
        return (serial, self._getNextTID(partition, oid, serial),
                compression, checksum, data, value_serial)

    def _changePartitionTable(self, cell_list, reset=False):
        q = self.query
        if reset:
            q("DELETE FROM pt")
        for offset, nid, state in cell_list:
            # TODO: this logic should move out of database manager
            # add 'dropCells(cell_list)' to API and use one query
            # WKRD: Why does SQLite need a statement journal file
            #       whereas we try to replace only 1 value ?
            #       We don't want to remove the 'NOT NULL' constraint
            #       so we must simulate a "REPLACE OR FAIL".
            q("DELETE FROM pt WHERE partition=? AND nid=?", (offset, nid))
            if state is not None:
                q("INSERT OR FAIL INTO pt VALUES (?,?,?)",
                  (offset, nid, int(state)))

    def dropPartitions(self, offset_list):
        where = " WHERE partition=?"
        q = self.query
        for partition in offset_list:
            args = partition,
            data_id_list = [x for x, in q(
                "SELECT DISTINCT data_id FROM obj%s AND data_id IS NOT NULL"
                % where, args)]
            q("DELETE FROM obj" + where, args)
            q("DELETE FROM trans" + where, args)
            self._pruneData(data_id_list)

    def _getUnfinishedDataIdList(self):
        return [x for x, in self.query(
            "SELECT data_id FROM tobj WHERE data_id IS NOT NULL")]

    def dropPartitionsTemporary(self, offset_list=None):
        where = "" if offset_list is None else \
            " WHERE `partition` IN (%s)" % ','.join(map(str, offset_list))
        q = self.query
        q("DELETE FROM tobj" + where)
        q("DELETE FROM ttrans" + where)

    def storeTransaction(self, tid, object_list, transaction, temporary=True):
        u64 = util.u64
        tid = u64(tid)
        T = 't' if temporary else ''
        obj_sql = "INSERT OR FAIL INTO %sobj VALUES (?,?,?,?,?)" % T
        q = self.query
        for oid, data_id, value_serial in object_list:
            oid = u64(oid)
            partition = self._getPartition(oid)
            if value_serial:
                value_serial = u64(value_serial)
                (data_id,), = q("SELECT data_id FROM obj"
                    " WHERE partition=? AND oid=? AND tid=?",
                    (partition, oid, value_serial))
                if temporary:
                    self.holdData(data_id)
            try:
                q(obj_sql, (partition, oid, tid, data_id, value_serial))
            except sqlite3.IntegrityError:
                # This may happen if a previous replication of 'obj' was
                # interrupted.
                if not T:
                    r, = q("SELECT data_id, value_tid FROM obj"
                           " WHERE partition=? AND oid=? AND tid=?",
                           (partition, oid, tid))
                    if r == (data_id, value_serial):
                        continue
                raise
        if transaction:
            oid_list, user, desc, ext, packed, ttid = transaction
            partition = self._getPartition(tid)
            assert packed in (0, 1)
            q("INSERT OR FAIL INTO %strans VALUES (?,?,?,?,?,?,?,?)" % T,
                (partition, None if temporary else tid,
                 packed, buffer(''.join(oid_list)),
                 buffer(user), buffer(desc), buffer(ext), u64(ttid)))

    def getOrphanList(self):
        return [x for x, in self.query(
            "SELECT id FROM data LEFT JOIN obj ON (id=data_id)"
            " WHERE data_id IS NULL")]

    def _pruneData(self, data_id_list):
        data_id_list = set(data_id_list).difference(self._uncommitted_data)
        if data_id_list:
            q = self.query
            data_id_list.difference_update(x for x, in q(
                "SELECT DISTINCT data_id FROM obj WHERE data_id IN (%s)"
                % ",".join(map(str, data_id_list))))
            q("DELETE FROM data WHERE id IN (%s)"
              % ",".join(map(str, data_id_list)))
            return len(data_id_list)
        return 0

    def storeData(self, checksum, oid, data, compression,
            _dup=unique_constraint_message("data", "hash", "compression")):
        H = buffer(checksum)
        p = self._getPartition(util.u64(oid))
        r = self._data_last_ids[p]
        try:
            self.query("INSERT INTO data VALUES (?,?,?,?)",
                (r, H, compression,  buffer(data)))
        except sqlite3.IntegrityError, e:
            if e.args[0] == _dup:
                (r, d), = self.query("SELECT id, value FROM data"
                                     " WHERE hash=? AND compression=?",
                                     (H, compression))
                if str(d) == data:
                    return r
            raise
        self._data_last_ids[p] = r + 1
        return r

    def loadData(self, data_id):
        return self.query("SELECT compression, hash, value"
                          " FROM data WHERE id=?", (data_id,)).fetchone()

    def _getDataTID(self, oid, tid=None, before_tid=None):
        partition = self._getReadablePartition(oid)
        sql = 'SELECT tid, value_tid FROM obj' \
              ' WHERE partition=? AND oid=?'
        if tid is not None:
            r = self.query(sql + ' AND tid=?', (partition, oid, tid))
        elif before_tid is not None:
            r = self.query(sql + ' AND tid<? ORDER BY tid DESC LIMIT 1',
                           (partition, oid, before_tid))
        else:
            r = self.query(sql + ' ORDER BY tid DESC LIMIT 1',
                           (partition, oid))
        r = r.fetchone()
        return r or (None, None)

    def lockTransaction(self, tid, ttid):
        u64 = util.u64
        self.query("UPDATE ttrans SET tid=? WHERE ttid=?",
                   (u64(tid), u64(ttid)))
        self.commit()

    def unlockTransaction(self, tid, ttid, trans, obj):
        q = self.query
        u64 = util.u64
        tid = u64(tid)
        if trans:
            q("INSERT INTO trans SELECT * FROM ttrans WHERE tid=?", (tid,))
            q("DELETE FROM ttrans WHERE tid=?", (tid,))
            if not obj:
                return
        ttid = u64(ttid)
        sql = " FROM tobj WHERE tid=?"
        data_id_list = [x for x, in q("SELECT data_id%s AND data_id IS NOT NULL"
                                      % sql, (ttid,))]
        q("INSERT INTO obj SELECT partition, oid, ?, data_id, value_tid" + sql,
          (tid, ttid))
        q("DELETE" + sql, (ttid,))
        self.releaseData(data_id_list)

    def abortTransaction(self, ttid):
        args = util.u64(ttid),
        q = self.query
        q("DELETE FROM tobj WHERE tid=?", args)
        q("DELETE FROM ttrans WHERE ttid=?", args)

    def deleteTransaction(self, tid):
        tid = util.u64(tid)
        self.query("DELETE FROM trans WHERE partition=? AND tid=?",
            (self._getPartition(tid), tid))

    def deleteObject(self, oid, serial=None):
        oid = util.u64(oid)
        sql = " FROM obj WHERE partition=? AND oid=?"
        args = [self._getPartition(oid), oid]
        if serial:
            sql += " AND tid=?"
            args.append(util.u64(serial))
        q = self.query
        data_id_list = [x for x, in q(
            "SELECT DISTINCT data_id%s AND data_id IS NOT NULL" % sql, args)]
        q("DELETE" + sql, args)
        self._pruneData(data_id_list)

    def _deleteRange(self, partition, min_tid=None, max_tid=None):
        sql = " WHERE partition=?"
        args = [partition]
        if min_tid is not None:
            sql += " AND ? < tid"
            args.append(min_tid)
        if max_tid is not None:
            sql += " AND tid <= ?"
            args.append(max_tid)
        q = self.query
        q("DELETE FROM trans" + sql, args)
        sql = " FROM obj" + sql
        data_id_list = [x for x, in q(
            "SELECT DISTINCT data_id%s AND data_id IS NOT NULL" % sql, args)]
        q("DELETE" + sql, args)
        self._pruneData(data_id_list)

    def getTransaction(self, tid, all=False):
        tid = util.u64(tid)
        q = self.query
        r = q("SELECT oids, user, description, ext, packed, ttid"
              " FROM trans WHERE partition=? AND tid=?",
              (self._getReadablePartition(tid), tid)).fetchone()
        if not r and all:
            r = q("SELECT oids, user, description, ext, packed, ttid"
                  " FROM ttrans WHERE tid=?", (tid,)).fetchone()
        if r:
            oids, user, description, ext, packed, ttid = r
            return splitOIDField(tid, oids), str(user), \
                str(description), str(ext), packed, util.p64(ttid)

    def getObjectHistory(self, oid, offset, length):
        # FIXME: This method doesn't take client's current transaction id as
        # parameter, which means it can return transactions in the future of
        # client's transaction.
        p64 = util.p64
        oid = util.u64(oid)
        return [(p64(tid), length or 0) for tid, length in self.query("""\
            SELECT tid, LENGTH(value)
                FROM obj LEFT JOIN data ON obj.data_id = data.id
                WHERE partition=? AND oid=? AND tid>=?
                ORDER BY tid DESC LIMIT ?,?""",
            (self._getReadablePartition(oid), oid,
             self._getPackTID(), offset, length))
            ] or None

    def _fetchObject(self, oid, tid):
        for serial, compression, checksum, data, value_serial in self.query(
                'SELECT tid, compression, data.hash, value, value_tid'
                ' FROM obj LEFT JOIN data ON obj.data_id = data.id'
                ' WHERE partition=? AND oid=? AND tid=?',
                (self._getReadablePartition(oid), oid, tid)):
            if checksum:
                checksum = str(checksum)
                data = str(data)
            return serial, compression, checksum, data, value_serial

    def getReplicationObjectList(self, min_tid, max_tid, length, partition,
            min_oid):
        u64 = util.u64
        p64 = util.p64
        min_tid = u64(min_tid)
        return [(p64(serial), p64(oid)) for serial, oid in self.query("""\
            SELECT tid, oid FROM obj
            WHERE partition=? AND tid<=?
            AND (tid=? AND ?<=oid OR ?<tid)
            ORDER BY tid ASC, oid ASC LIMIT ?""",
            (partition, u64(max_tid), min_tid, u64(min_oid), min_tid, length))]

    def _getTIDList(self, offset, length, partition_list):
        return (t[0] for t in self.query(
            "SELECT tid FROM trans WHERE `partition` in (%s)"
            " ORDER BY tid DESC LIMIT %d,%d"
            % (','.join(map(str, partition_list)), offset, length)))

    def getReplicationTIDList(self, min_tid, max_tid, length, partition):
        u64 = util.u64
        p64 = util.p64
        min_tid = u64(min_tid)
        max_tid = u64(max_tid)
        return [p64(t[0]) for t in self.query("""\
            SELECT tid FROM trans
            WHERE partition=? AND ?<=tid AND tid<=?
            ORDER BY tid ASC LIMIT ?""",
            (partition, min_tid, max_tid, length))]

    def _updatePackFuture(self, oid, orig_serial, max_serial):
        # Before deleting this objects revision, see if there is any
        # transaction referencing its value at max_serial or above.
        # If there is, copy value to the first future transaction. Any further
        # reference is just updated to point to the new data location.
        partition = self._getReadablePartition(oid)
        value_serial = None
        q = self.query
        for T in '', 't':
            update = """UPDATE OR FAIL %sobj SET value_tid=?
                         WHERE partition=? AND oid=? AND tid=?""" % T
            for serial, in q("""SELECT tid FROM %sobj
                    WHERE partition=? AND oid=? AND tid>=? AND value_tid=?
                    ORDER BY tid ASC""" % T,
                    (partition, oid, max_serial, orig_serial)):
                q(update, (value_serial, partition, oid, serial))
                if value_serial is None:
                    # First found, mark its serial for future reference.
                    value_serial = serial
        return value_serial

    def pack(self, tid, updateObjectDataForPack):
        # TODO: unit test (along with updatePackFuture)
        p64 = util.p64
        tid = util.u64(tid)
        updatePackFuture = self._updatePackFuture
        getPartition = self._getReadablePartition
        q = self.query
        self._setPackTID(tid)
        for count, oid, max_serial in q("SELECT COUNT(*) - 1, oid, MAX(tid)"
                                        " FROM obj WHERE tid<=? GROUP BY oid",
                                        (tid,)):
            partition = getPartition(oid)
            if q("SELECT 1 FROM obj WHERE partition=?"
                 " AND oid=? AND tid=? AND data_id IS NULL",
                 (partition, oid, max_serial)).fetchone():
                max_serial += 1
            elif not count:
                continue
            # There are things to delete for this object
            data_id_set = set()
            sql = " FROM obj WHERE partition=? AND oid=? AND tid<?"
            args = partition, oid, max_serial
            for serial, data_id in q("SELECT tid, data_id" + sql, args):
                data_id_set.add(data_id)
                new_serial = updatePackFuture(oid, serial, max_serial)
                if new_serial:
                    new_serial = p64(new_serial)
                updateObjectDataForPack(p64(oid), p64(serial),
                                        new_serial, data_id)
            q("DELETE" + sql, args)
            data_id_set.discard(None)
            self._pruneData(data_id_set)
        self.commit()

    def checkTIDRange(self, partition, length, min_tid, max_tid):
        # XXX: SQLite's GROUP_CONCAT is slow (looks like quadratic)
        count, tids, max_tid = self.query("""\
            SELECT COUNT(*), GROUP_CONCAT(tid), MAX(tid)
            FROM (SELECT tid FROM trans
                  WHERE partition=? AND ?<=tid AND tid<=?
                  ORDER BY tid ASC LIMIT ?) AS t""",
            (partition, util.u64(min_tid), util.u64(max_tid),
             -1 if length is None else length)).fetchone()
        if count:
            return count, sha1(tids).digest(), util.p64(max_tid)
        return 0, ZERO_HASH, ZERO_TID

    def checkSerialRange(self, partition, length, min_tid, max_tid, min_oid):
        u64 = util.u64
        # We don't ask SQLite to compute everything (like in checkTIDRange)
        # because it's difficult to get the last serial _for the last oid_.
        # We would need a function (that could be named 'LAST') that returns the
        # last grouped value, instead of the greatest one.
        min_tid = u64(min_tid)
        r = self.query("""\
            SELECT tid, oid
            FROM obj
            WHERE partition=? AND tid<=? AND (tid>? OR tid=? AND oid>=?)
            ORDER BY tid, oid LIMIT ?""",
            (partition, u64(max_tid), min_tid, min_tid, u64(min_oid),
             -1 if length is None else length)).fetchall()
        if r:
            p64 = util.p64
            return (len(r),
                    sha1(','.join(str(x[0]) for x in r)).digest(),
                    p64(r[-1][0]),
                    sha1(','.join(str(x[1]) for x in r)).digest(),
                    p64(r[-1][1]))
        return 0, ZERO_HASH, ZERO_TID, ZERO_HASH, ZERO_OID

    def dump(self):
        main = []
        data = []
        for line in self.conn.iterdump():
            if line.startswith('INSERT '):
                assert line.endswith(';'), line
                data.append(line)
                continue
            if line.startswith('CREATE TABLE '):
                # ALTER TABLE adds quotes.
                create, table, name, tail = line.split(' ', 3)
                line = ' '.join((create, table, name.strip('"'), tail))
            main.append(line)
        assert line == 'COMMIT;', line
        data.sort()
        main[-1:-1] = data
        return '\n'.join(main) + '\n'

    def _restore(self, sql):
        self.conn.executescript(sql)
