# coding: utf-8
# copyright 2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This file is part of CubicWeb.
#
# CubicWeb is free software: you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation, either version 2.1 of the License, or (at your option)
# any later version.
#
# CubicWeb 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 Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License along
# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.

import logging
from datetime import datetime
from collections import defaultdict
from io import StringIO

from six.moves import range

from yams.constraints import SizeConstraint

from psycopg2 import ProgrammingError

from cubicweb.server.schema2sql import rschema_has_table
from cubicweb.schema import PURE_VIRTUAL_RTYPES
from cubicweb.dataimport import stores, pgstore
from cubicweb.utils import make_uid
from cubicweb.server.sqlutils import SQL_PREFIX


class MassiveObjectStore(stores.RQLObjectStore):
    """
    Store for massive import of data, with delayed insertion of meta data.

    WARNINGS:
   - This store may be only used with PostgreSQL for now, as it relies
     on the COPY FROM method, and on specific PostgreSQL tables to get all
     the indexes.
   - This store can only insert relations that are not inlined (i.e.,
     which do *not* have inlined=True in their definition in the schema).

   It should be used as follows:

       store = MassiveObjectStore(cnx)
       store.init_rtype_table('Person', 'lives_in', 'Location')
       ...

       store.prepare_insert_entity('Person', subj_iid_attribute=person_iid, ...)
       store.prepare_insert_entity('Location', obj_iid_attribute=location_iid, ...)
       ...

       # subj_iid_attribute and obj_iid_attribute are argument names
       # chosen by the user (e.g. "cwuri"). These names can be identical.
       # person_iid and location_iid are unique IDs and depend on the data
       # (e.g URI).
       store.flush()
       store.relate_by_iid(person_iid, 'lives_in', location_iid)
       # For example:
       store.prepare_insert_entity('Person',
                                   cwuri='http://dbpedia.org/toto',
                                   name='Toto')
       store.prepare_insert_entity('Location',
                                   uri='http://geonames.org/11111',
                                   name='Somewhere')
       store.flush()
       store.relate_by_iid('http://dbpedia.org/toto',
                           'lives_in',
                           'http://geonames.org/11111')
       # Finally
       store.convert_relations('Person', 'lives_in', 'Location',
                               'subj_iid_attribute', 'obj_iid_attribute')
       # For the previous example:
       store.convert_relations('Person', 'lives_in', 'Location', 'cwuri', 'uri')
       ...
       store.commit()
       store.finish()
    """
    # max size of the iid, used to create the iid_eid conversion table
    iid_maxsize = 1024

    def __init__(self, cnx,
                 on_commit_callback=None, on_rollback_callback=None,
                 slave_mode=False,
                 source=None,
                 eids_seq_range=10000):
        """ Create a MassiveObject store, with the following attributes:

        - cnx: CubicWeb cnx
        - eids_seq_range: size of eid range reserved by the store for each batch
        """
        super(MassiveObjectStore, self).__init__(cnx)
        self.logger = logging.getLogger('dataimport.massive_store')
        self._cnx = cnx
        self.sql = cnx.system_sql
        self._data_uri_relations = defaultdict(list)
        self.eids_seq_range = eids_seq_range

        # etypes for which we have a uri_eid_%(etype)s table
        self._init_uri_eid = set()
        # etypes for which we have a uri_eid_%(e)s_idx index
        self._uri_eid_inserted = set()
        # set of rtypes for which we have a %(rtype)s_relation_iid_tmp table
        self._uri_rtypes = set()
        # set of etypes whose tables are created
        self._entities = set()
        # set of rtypes for which we have a %(rtype)s_relation_tmp table
        self._rtypes = set()

        self.slave_mode = slave_mode
        self.default_values = get_default_values(cnx.vreg.schema)
        pg_schema = cnx.repo.config.system_source_config.get('db-namespace') or 'public'
        self._dbh = PGHelper(self._cnx, pg_schema)
        self._data_entities = defaultdict(list)
        self._data_relations = defaultdict(list)
        self._now = datetime.utcnow()
        self._default_cwuri = make_uid('_auto_generated')
        self._count_cwuri = 0
        self.on_commit_callback = on_commit_callback
        self.on_rollback_callback = on_rollback_callback
        # Do our meta tables already exist?
        self._init_massive_metatables()
        self.get_next_eid = lambda g=self._get_eid_gen(): next(g)
        # recreate then when self.finish() is called

        if not self.slave_mode:
            self._drop_all_constraints()
            self._drop_metatables_constraints()
        if source is None:
            source = cnx.repo.system_source
        self.source = source
        self._etype_eid_idx = dict(cnx.execute('Any XN,X WHERE X is CWEType, X name XN'))
        cnx.read_security = False
        cnx.write_security = False

    ### INIT FUNCTIONS ########################################################

    def _drop_all_constraints(self):
        schema = self._cnx.vreg.schema
        tables = ['cw_%s' % etype.type.lower()
                  for etype in schema.entities() if not etype.final]
        for rschema in schema.relations():
            if rschema.inlined:
                continue
            elif rschema_has_table(rschema, skip_relations=PURE_VIRTUAL_RTYPES):
                tables.append('%s_relation' % rschema.type.lower())
        tables.append('entities')
        for tablename in tables:
            self._store_and_drop_constraints(tablename)

    def _store_and_drop_constraints(self, tablename):
        if not self._constraint_table_created:
            # Create a table to save the constraints
            # Allow reload even after crash
            sql = "CREATE TABLE cwmassive_constraints (origtable text, query text, type varchar(256))"
            self.sql(sql)
            self._constraint_table_created = True
        constraints = self._dbh.application_constraints(tablename)
        for name, query in constraints.items():
            sql = 'INSERT INTO cwmassive_constraints VALUES (%(e)s, %(c)s, %(t)s)'
            self.sql(sql, {'e': tablename, 'c': query, 't': 'constraint'})
            sql = 'ALTER TABLE %s DROP CONSTRAINT %s' % (tablename, name)
            self.sql(sql)

    def reapply_all_constraints(self):
        if not self._dbh.table_exists('cwmassive_constraints'):
            self.logger.info('The table cwmassive_constraints does not exist')
            return
        sql = 'SELECT query FROM cwmassive_constraints WHERE type = %(t)s'
        crs = self.sql(sql, {'t': 'constraint'})
        for query, in crs.fetchall():
            self.sql(query)
            self.sql('DELETE FROM cwmassive_constraints WHERE type = %(t)s '
                     'AND query = %(q)s', {'t': 'constraint', 'q': query})

    def init_rtype_table(self, etype_from, rtype, etype_to):
        """ Build temporary table for standard rtype """
        # Create an uri_eid table for each etype for a better
        # control of which etype is concerned by a particular
        # possibly multivalued relation.
        for etype in (etype_from, etype_to):
            if etype and etype not in self._init_uri_eid:
                self._init_uri_eid_table(etype)
        if rtype not in self._uri_rtypes:
            # Create the temporary table
            if not self._cnx.repo.schema.rschema(rtype).inlined:
                try:
                    sql = 'CREATE TABLE %(r)s_relation_iid_tmp (uri_from character ' \
                          'varying(%(s)s), uri_to character varying(%(s)s))'
                    self.sql(sql % {'r': rtype, 's': self.iid_maxsize})
                except ProgrammingError:
                    # XXX Already exist (probably due to multiple import)
                    pass
            else:
                self.logger.warning("inlined relation %s: cannot insert it", rtype)
            # Add it to the initialized set
            self._uri_rtypes.add(rtype)

    def _init_uri_eid_table(self, etype):
        """ Build a temporary table for id/eid convertion
        """
        try:
            sql = "CREATE TABLE uri_eid_%(e)s (uri character varying(%(size)s), eid integer)"
            self.sql(sql % {'e': etype.lower(), 'size': self.iid_maxsize,})
        except ProgrammingError:
            # XXX Already exist (probably due to multiple import)
            pass
        # Add it to the initialized set
        self._init_uri_eid.add(etype)

    def _init_massive_metatables(self):
        # Check if our tables are not already created (i.e. a restart)
        self._initialized_table_created = self._dbh.table_exists('cwmassive_initialized')
        self._constraint_table_created = self._dbh.table_exists('cwmassive_constraints')
        self._metadata_table_created = self._dbh.table_exists('cwmassive_metadata')

    ### RELATE FUNCTION #######################################################

    def relate_by_iid(self, iid_from, rtype, iid_to):
        """Add new relation based on the internal id (iid)
        of the entities (not the eid)"""
        # Push data
        if isinstance(iid_from, unicode):
            iid_from = iid_from.encode('utf-8')
        if isinstance(iid_to, unicode):
            iid_to = iid_to.encode('utf-8')
        self._data_uri_relations[rtype].append({'uri_from': iid_from, 'uri_to': iid_to})

    ### FLUSH FUNCTIONS #######################################################

    def flush_relations(self):
        """ Flush the relations data
        """
        for rtype, data in self._data_uri_relations.items():
            if not data:
                self.logger.info('No data for rtype %s', rtype)
            buf = StringIO('\n'.join(['%(uri_from)s\t%(uri_to)s' % d for d in data]))
            if not buf:
                self.logger.info('Empty Buffer for rtype %s', rtype)
                continue
            cursor = self._cnx.cnxset.cu
            if not self._cnx.repo.schema.rschema(rtype).inlined:
                cursor.copy_from(buf, '%s_relation_iid_tmp' % rtype.lower(),
                                 null='NULL', columns=('uri_from', 'uri_to'))
            else:
                self.logger.warning("inlined relation %s: cannot insert it", rtype)
            buf.close()
            # Clear data cache
            self._data_uri_relations[rtype] = []

    def fill_uri_eid_table(self, etype, uri_label):
        """ Fill the uri_eid table
        """
        self.logger.info('Fill uri_eid for etype %s', etype)
        sql = 'INSERT INTO uri_eid_%(e)s SELECT cw_%(l)s, cw_eid FROM cw_%(e)s'
        self.sql(sql % {'l': uri_label, 'e': etype.lower()})
        # Add indexes
        self.sql('CREATE INDEX uri_eid_%(e)s_idx ON uri_eid_%(e)s' '(uri)' % {'e': etype.lower()})
        # Set the etype as converted
        self._uri_eid_inserted.add(etype)

    def convert_relations(self, etype_from, rtype, etype_to,
                          uri_label_from='cwuri', uri_label_to='cwuri'):
        """ Flush the converted relations
        """
        # Always flush relations to be sure
        self.logger.info('Convert relations %s %s %s', etype_from, rtype, etype_to)
        self.flush_relations()
        if uri_label_from and etype_from not in self._uri_eid_inserted:
            self.fill_uri_eid_table(etype_from, uri_label_from)
        if uri_label_to and etype_to not in self._uri_eid_inserted:
            self.fill_uri_eid_table(etype_to, uri_label_to)
        if self._cnx.repo.schema.rschema(rtype).inlined:
            self.logger.warning("Can't insert inlined relation %s", rtype)
            return
        if uri_label_from and uri_label_to:
            sql = '''INSERT INTO %(r)s_relation (eid_from, eid_to) SELECT DISTINCT O1.eid, O2.eid
            FROM %(r)s_relation_iid_tmp AS T, uri_eid_%(ef)s as O1, uri_eid_%(et)s as O2
            WHERE O1.uri=T.uri_from AND O2.uri=T.uri_to AND NOT EXISTS (
            SELECT 1 FROM %(r)s_relation AS TT WHERE TT.eid_from=O1.eid AND TT.eid_to=O2.eid);
            '''
        elif uri_label_to:
            sql = '''INSERT INTO %(r)s_relation (eid_from, eid_to) SELECT DISTINCT
            CAST(T.uri_from AS INTEGER), O1.eid
            FROM %(r)s_relation_iid_tmp AS T, uri_eid_%(et)s as O1
            WHERE O1.uri=T.uri_to AND NOT EXISTS (
            SELECT 1 FROM %(r)s_relation AS TT WHERE
            TT.eid_from=CAST(T.uri_from AS INTEGER) AND TT.eid_to=O1.eid);
            '''
        elif uri_label_from:
            sql = '''INSERT INTO %(r)s_relation (eid_from, eid_to) SELECT DISTINCT O1.eid, T.uri_to
            O1.eid, CAST(T.uri_to AS INTEGER)
            FROM %(r)s_relation_iid_tmp AS T, uri_eid_%(ef)s as O1
            WHERE O1.uri=T.uri_from AND NOT EXISTS (
            SELECT 1 FROM %(r)s_relation AS TT WHERE
            TT.eid_from=O1.eid AND TT.eid_to=CAST(T.uri_to AS INTEGER));
            '''
        try:
            self.sql(sql % {'r': rtype.lower(),
                            'et': etype_to.lower() if etype_to else u'',
                            'ef': etype_from.lower() if etype_from else u''})
        except Exception as ex:
            self.logger.error("Can't insert relation %s: %s", rtype, ex)

    ### SQL UTILITIES #########################################################

    def drop_and_store_indexes(self, tablename):
        # Drop indexes and constraints
        if not self._constraint_table_created:
            # Create a table to save the constraints
            # Allow reload even after crash
            sql = "CREATE TABLE cwmassive_constraints (origtable text, query text, type varchar(256))"
            self.sql(sql)
            self._constraint_table_created = True
        self._drop_table_indexes(tablename)

    def _drop_table_indexes(self, tablename):
        """ Drop and store table constraints and indexes """
        indexes = self._dbh.application_indexes(tablename)
        for name, query in indexes.items():
            sql = 'INSERT INTO cwmassive_constraints VALUES (%(e)s, %(c)s, %(t)s)'
            self.sql(sql, {'e': tablename, 'c': query, 't': 'index'})
            sql = 'DROP INDEX %s' % name
            self.sql(sql)

    def reapply_constraint_index(self, tablename):
        if not self._dbh.table_exists('cwmassive_constraints'):
            self.logger.info('The table cwmassive_constraints does not exist')
            return
        sql = 'SELECT query FROM cwmassive_constraints WHERE origtable = %(e)s'
        crs = self.sql(sql, {'e': tablename})
        for query, in crs.fetchall():
            self.sql(query)
            self.sql('DELETE FROM cwmassive_constraints WHERE origtable = %(e)s '
                     'AND query = %(q)s', {'e': tablename, 'q': query})

    def _drop_metatables_constraints(self):
        """ Drop all the constraints for the meta data"""
        for tablename in ('created_by_relation', 'owned_by_relation',
                          'is_instance_of_relation', 'is_relation',
                          'entities'):
            self.drop_and_store_indexes(tablename)

    def _create_metatables_constraints(self):
        """ Create all the constraints for the meta data"""
        for tablename in ('entities',
                          'created_by_relation', 'owned_by_relation',
                          'is_instance_of_relation', 'is_relation'):
            # Indexes and constraints
            self.reapply_constraint_index(tablename)

    def init_relation_table(self, rtype):
        """ Get and remove all indexes for performance sake """
        # Create temporary table
        if not self.slave_mode and rtype not in self._rtypes:
            sql = "CREATE TABLE %s_relation_tmp (eid_from integer, eid_to integer)" % rtype.lower()
            self.sql(sql)
            # Drop indexes and constraints
            tablename = '%s_relation' % rtype.lower()
            self.drop_and_store_indexes(tablename)
            # Push the etype in the initialized table for easier restart
            self.init_create_initialized_table()
            sql = 'INSERT INTO cwmassive_initialized VALUES (%(e)s, %(t)s)'
            self.sql(sql, {'e': rtype, 't': 'rtype'})
            # Mark rtype as "initialized" for faster check
            self._rtypes.add(rtype)

    def init_create_initialized_table(self):
        """ Create the cwmassive initialized table
        """
        if not self._initialized_table_created:
            sql = "CREATE TABLE cwmassive_initialized (retype text, type varchar(128))"
            self.sql(sql)
            self._initialized_table_created = True

    def init_etype_table(self, etype):
        """ Add eid sequence to a particular etype table and
        remove all indexes for performance sake """
        if etype not in self._entities:
            # Only for non-initialized etype and not slave mode store
            if not self.slave_mode:
                # Drop indexes and constraints
                tablename = 'cw_%s' % etype.lower()
                self.drop_and_store_indexes(tablename)
                # Push the etype in the initialized table for easier restart
                self.init_create_initialized_table()
                sql = 'INSERT INTO cwmassive_initialized VALUES (%(e)s, %(t)s)'
                self.sql(sql, {'e': etype, 't': 'etype'})
            # Mark etype as "initialized" for faster check
            self._entities.add(etype)

    def restart_eid_sequence(self, start_eid):
        self._cnx.system_sql(self._cnx.repo.system_source.dbhelper.sql_restart_numrange(
            'entities_id_seq', initial_value=start_eid))
        self._cnx.commit()

    ### ENTITIES CREATION #####################################################

    def _get_eid_gen(self):
        """ Function getting the next eid. This is done by preselecting
        a given number of eids from the 'entities_id_seq', and then
        storing them"""
        while True:
            last_eid = self._cnx.repo.system_source.create_eid(self._cnx, self.eids_seq_range)
            for eid in range(last_eid - self.eids_seq_range + 1, last_eid + 1):
                yield eid

    def _apply_default_values(self, etype, kwargs):
        """Apply the default values for a given etype, attribute and value."""
        default_values = self.default_values[etype]
        missing_keys = set(default_values) - set(kwargs)
        kwargs.update((key, default_values[key]) for key in missing_keys)

    # store api ################################################################

    def prepare_insert_entity(self, etype, **kwargs):
        """Given an entity type, attributes and inlined relations, returns the inserted entity's
        eid.
        """
        # Init the table if necessary
        self.init_etype_table(etype)
        # Add meta data if not given
        if 'modification_date' not in kwargs:
            kwargs['modification_date'] = self._now
        if 'creation_date' not in kwargs:
            kwargs['creation_date'] = self._now
        if 'cwuri' not in kwargs:
            kwargs['cwuri'] = self._default_cwuri + str(self._count_cwuri)
            self._count_cwuri += 1
        if 'eid' not in kwargs:
            # If eid is not given and the eids sequence is set,
            # use the value from the sequence
            kwargs['eid'] = self.get_next_eid()
        self._apply_default_values(etype, kwargs)
        self._data_entities[etype].append(kwargs)
        return kwargs.get('eid')

    def prepare_insert_relation(self, eid_from, rtype, eid_to, **kwargs):
        """Insert into the database a  relation ``rtype`` between entities with eids ``eid_from``
        and ``eid_to``.
        """
        # Init the table if necessary
        self.init_relation_table(rtype)
        self._data_relations[rtype].append({'eid_from': eid_from, 'eid_to': eid_to})

    def flush(self):
        """Flush the data"""
        self.flush_entities()
        self.flush_internal_relations()
        self.flush_relations()

    def commit(self):
        """Commit the database transaction."""
        self.on_commit()
        super(MassiveObjectStore, self).commit()

    def finish(self):
        """Remove temporary tables and columns."""
        self.logger.info("Start cleaning")
        if self.slave_mode:
            raise RuntimeError('Store cleanup is not allowed in slave mode')
        self.logger.info("Start cleaning")
        # Cleanup relations tables
        for etype in self._init_uri_eid:
            self.sql('DROP TABLE uri_eid_%s' % etype.lower())
        # Remove relations tables
        for rtype in self._uri_rtypes:
            if not self._cnx.repo.schema.rschema(rtype).inlined:
                self.sql('DROP TABLE %(r)s_relation_iid_tmp' % {'r': rtype})
            else:
                self.logger.warning("inlined relation %s: no cleanup to be done for it" % rtype)
        # Create meta constraints (entities, is_instance_of, ...)
        self._create_metatables_constraints()
        # Get all the initialized etypes/rtypes
        if self._dbh.table_exists('cwmassive_initialized'):
            crs = self.sql('SELECT retype, type FROM cwmassive_initialized')
            for retype, _type in crs.fetchall():
                self.logger.info('Cleanup for %s' % retype)
                if _type == 'etype':
                    # Cleanup entities tables - Recreate indexes
                    self._cleanup_entities(retype)
                elif _type == 'rtype':
                    # Cleanup relations tables
                    self._cleanup_relations(retype)
                self.sql('DELETE FROM cwmassive_initialized WHERE retype = %(e)s',
                         {'e': retype})
        self.reapply_all_constraints()
        # Delete the meta data table
        for table_name in ('cwmassive_initialized', 'cwmassive_constraints', 'cwmassive_metadata'):
            if self._dbh.table_exists(table_name):
                self.sql('DROP TABLE %s' % table_name)
        self.commit()

    ### FLUSH #################################################################

    def on_commit(self):
        if self.on_commit_callback:
            self.on_commit_callback()

    def on_rollback(self, exc, etype, data):
        if self.on_rollback_callback:
            self.on_rollback_callback(exc, etype, data)
            self._cnx.rollback()
        else:
            raise exc

    def flush_internal_relations(self):
        """ Flush the relations data
        """
        for rtype, data in self._data_relations.items():
            if not data:
                # There is no data for these etype for this flush round.
                continue
            buf = pgstore._create_copyfrom_buffer(data, ('eid_from', 'eid_to'))
            if not buf:
                # The buffer is empty. This is probably due to error in _create_copyfrom_buffer
                raise ValueError
            cursor = self._cnx.cnxset.cu
            # Push into the tmp table
            cursor.copy_from(buf, '%s_relation_tmp' % rtype.lower(),
                             null='NULL', columns=('eid_from', 'eid_to'))
            # Clear data cache
            self._data_relations[rtype] = []

    def flush_entities(self):
        """ Flush the entities data
        """
        for etype, data in self._data_entities.items():
            if not data:
                # There is no data for these etype for this flush round.
                continue
            # XXX It may be interresting to directly infer the columns'
            # names from the schema instead of using .keys()
            columns = data[0].keys()
            # XXX For now, the _create_copyfrom_buffer does a "row[column]"
            # which can lead to a key error.
            # Thus we should create dictionary with all the keys.
            columns = set()
            for d in data:
                columns.update(d.keys())
            _data = []
            _base_data = dict.fromkeys(columns)
            for d in data:
                _d = _base_data.copy()
                _d.update(d)
                _data.append(_d)
            buf = pgstore._create_copyfrom_buffer(_data, columns)
            if not buf:
                # The buffer is empty. This is probably due to error in _create_copyfrom_buffer
                raise ValueError('Error in buffer creation for etype %s' % etype)
            columns = ['cw_%s' % attr for attr in columns]
            cursor = self._cnx.cnxset.cu
            try:
                cursor.copy_from(buf, 'cw_%s' % etype.lower(), null='NULL', columns=columns)
            except Exception as exc:
                self.on_rollback(exc, etype, data)
            # Clear data cache
            self._data_entities[etype] = []
        if not self.slave_mode:
            self.flush_meta_data()

    def flush_meta_data(self):
        """ Flush the meta data (entities table, is_instance table, ...)
        """
        if self.slave_mode:
            raise RuntimeError('Flushing meta data is not allow in slave mode')
        if not self._dbh.table_exists('cwmassive_initialized'):
            self.logger.info('No information available for initialized etypes/rtypes')
            return
        if not self._metadata_table_created:
            # Keep the correctly flush meta data in database
            sql = "CREATE TABLE cwmassive_metadata (etype text)"
            self.sql(sql)
            self._metadata_table_created = True
        crs = self.sql('SELECT etype FROM cwmassive_metadata')
        already_flushed = set(e for e, in crs.fetchall())
        crs = self.sql('SELECT retype FROM cwmassive_initialized WHERE type = %(t)s',
                       {'t': 'etype'})
        all_etypes = set(e for e, in crs.fetchall())
        for etype in all_etypes:
            if etype not in already_flushed:
                # Deals with meta data
                self.logger.info('Flushing meta data for %s' % etype)
                self.insert_massive_meta_data(etype)
                sql = 'INSERT INTO cwmassive_metadata VALUES (%(e)s)'
                self.sql(sql, {'e': etype})

    def _cleanup_entities(self, etype):
        """ Cleanup etype table """
        # Create indexes and constraints
        tablename = SQL_PREFIX + etype.lower()
        self.reapply_constraint_index(tablename)

    def _cleanup_relations(self, rtype):
        """ Cleanup rtype table """
        # Push into relation table while removing duplicate
        sql = '''INSERT INTO %(r)s_relation (eid_from, eid_to) SELECT DISTINCT
                 T.eid_from, T.eid_to FROM %(r)s_relation_tmp AS T
                 WHERE NOT EXISTS (SELECT 1 FROM %(r)s_relation AS TT WHERE
                 TT.eid_from=T.eid_from AND TT.eid_to=T.eid_to);''' % {'r': rtype}
        self.sql(sql)
        # Drop temporary relation table
        sql = ('DROP TABLE %(r)s_relation_tmp' % {'r': rtype.lower()})
        self.sql(sql)
        # Create indexes and constraints
        tablename = '%s_relation' % rtype.lower()
        self.reapply_constraint_index(tablename)

    def insert_massive_meta_data(self, etype):
        """ Massive insertion of meta data for a given etype, based on SQL statements.
        """
        # Push data - Use coalesce to avoid NULL (and get 0), if there is no
        # entities of this type in the entities table.
        # Meta data relations
        self.metagen_push_relation(etype, self._cnx.user.eid, 'created_by_relation')
        self.metagen_push_relation(etype, self._cnx.user.eid, 'owned_by_relation')
        self.metagen_push_relation(etype, self.source.eid, 'cw_source_relation')
        self.metagen_push_relation(etype, self._etype_eid_idx[etype], 'is_relation')
        self.metagen_push_relation(etype, self._etype_eid_idx[etype], 'is_instance_of_relation')
        sql = ("INSERT INTO entities (eid, type, asource, extid) "
               "SELECT cw_eid, '%s', 'system', NULL FROM cw_%s "
               "WHERE NOT EXISTS (SELECT 1 FROM entities WHERE eid=cw_eid)"
               % (etype, etype.lower()))
        self.sql(sql)

    def metagen_push_relation(self, etype, eid_to, rtype):
        sql = ("INSERT INTO %s (eid_from, eid_to) SELECT cw_eid, %s FROM cw_%s "
               "WHERE NOT EXISTS (SELECT 1 FROM entities WHERE eid=cw_eid)"
               % (rtype, eid_to, etype.lower()))
        self.sql(sql)


### CONSTRAINTS MANAGEMENT FUNCTIONS  ##########################################

def get_size_constraints(schema):
    """analyzes yams ``schema`` and returns the list of size constraints.

    The returned value is a dictionary mapping entity types to a
    sub-dictionnaries mapping attribute names -> max size.
    """
    size_constraints = {}
    # iterates on all entity types
    for eschema in schema.entities():
        # for each entity type, iterates on attribute definitions
        size_constraints[eschema.type] = eschema_constraints = {}
        for rschema, aschema in eschema.attribute_definitions():
            # for each attribute, if a size constraint is found,
            # append it to the size constraint list
            maxsize = None
            rdef = rschema.rdef(eschema, aschema)
            for constraint in rdef.constraints:
                if isinstance(constraint, SizeConstraint):
                    maxsize = constraint.max
                    eschema_constraints[rschema.type] = maxsize
    return size_constraints

def get_default_values(schema):
    """analyzes yams ``schema`` and returns the list of default values.

    The returned value is a dictionary mapping entity types to a
    sub-dictionnaries mapping attribute names -> default values.
    """
    default_values = {}
    # iterates on all entity types
    for eschema in schema.entities():
        # for each entity type, iterates on attribute definitions
        default_values[eschema.type] = eschema_constraints = {}
        for rschema, _ in eschema.attribute_definitions():
            # for each attribute, if a size constraint is found,
            # append it to the size constraint list
            if eschema.default(rschema.type) is not None:
                eschema_constraints[rschema.type] = eschema.default(rschema.type)
    return default_values


class PGHelper(object):
    def __init__(self, cnx, pg_schema='public'):
        self.cnx = cnx
        # Deals with pg schema, see #3216686
        self.pg_schema = pg_schema

    def application_indexes_constraints(self, tablename):
        """ Get all the indexes/constraints for a given tablename """
        indexes = self.application_indexes(tablename)
        constraints = self.application_constraints(tablename)
        _indexes = {}
        for name, query in indexes.items():
            # Remove pkey indexes (automatically created by constraints)
            # Specific cases of primary key, see #3224079
            if name not in constraints:
                _indexes[name] = query
        return _indexes, constraints

    def table_exists(self, table_name):
        sql = "SELECT * from information_schema.tables WHERE table_name=%(t)s AND table_schema=%(s)s"
        crs = self.cnx.system_sql(sql, {'t': table_name, 's': self.pg_schema})
        res = crs.fetchall()
        if res:
            return True
        return False

    # def check_if_primary_key_exists_for_table(self, table_name):
    #     sql = ("SELECT constraint_name FROM information_schema.table_constraints "
    #            "WHERE constraint_type = 'PRIMARY KEY' AND table_name=%(t)s AND table_schema=%(s)s")
    #     crs = self.cnx.system_sql(sql, {'t': table_name, 's': self.pg_schema})
    #     res = crs.fetchall()
    #     if res:
    #         return True
    #     return False

    def index_query(self, name):
        """Get the request to be used to recreate the index"""
        return self.cnx.system_sql("SELECT pg_get_indexdef(c.oid) "
                                   "from pg_catalog.pg_class c "
                                   "LEFT JOIN pg_catalog.pg_namespace n "
                                   "ON n.oid = c.relnamespace "
                                   "WHERE c.relname = %(r)s AND n.nspname=%(n)s",
                                   {'r': name, 'n': self.pg_schema}).fetchone()[0]

    def constraint_query(self, name):
        """Get the request to be used to recreate the constraint"""
        return self.cnx.system_sql("SELECT pg_get_constraintdef(c.oid) "
                                   "from pg_catalog.pg_constraint c "
                                   "LEFT JOIN pg_catalog.pg_namespace n "
                                   "ON n.oid = c.connamespace "
                                   "WHERE c.conname = %(r)s AND n.nspname=%(n)s",
                                   {'r': name, 'n': self.pg_schema}).fetchone()[0]

    def index_list(self, tablename):
        # This SQL query (cf http://www.postgresql.org/message-id/432F450F.4080700@squiz.net)
        # aims at getting all the indexes for each table.
        sql = '''SELECT c.relname as "Name"
        FROM pg_catalog.pg_class c
        JOIN pg_catalog.pg_index i ON i.indexrelid = c.oid
        JOIN pg_catalog.pg_class c2 ON i.indrelid = c2.oid
        LEFT JOIN pg_catalog.pg_user u ON u.usesysid = c.relowner
        LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
        WHERE c.relkind IN ('i','')
        AND c2.relname = '%s'
        AND i.indisprimary = FALSE
        AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
        AND pg_catalog.pg_table_is_visible(c.oid);''' % tablename
        return self.cnx.system_sql(sql).fetchall()

    def application_indexes(self, tablename):
        """ Iterate over all the indexes """
        indexes_list = self.index_list(tablename)
        indexes = {}
        for name, in indexes_list:
            indexes[name] = self.index_query(name)
        return indexes

    def constraint_list(self, tablename):
        sql = '''SELECT i.conname as "Name"
                 FROM pg_catalog.pg_class c
                 JOIN pg_catalog.pg_constraint i ON i.conrelid = c.oid
                 JOIN pg_catalog.pg_class c2 ON i.conrelid=c2.oid
                 LEFT JOIN pg_catalog.pg_user u ON u.usesysid = c.relowner
                 LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
                 WHERE
                   c2.relname = '%s'
                   AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
                   AND pg_catalog.pg_table_is_visible(c.oid)
                 ''' % tablename
        return self.cnx.system_sql(sql).fetchall()

    def application_constraints(self, tablename):
        """ Iterate over all the constraints """
        constraint_list = self.constraint_list(tablename)
        constraints = {}
        for name, in constraint_list:
            query = self.constraint_query(name)
            constraints[name] = 'ALTER TABLE %s ADD CONSTRAINT %s %s' % (tablename, name, query)
        return constraints