import re

from django.db.backends import BaseDatabaseOperations

server_version_re = re.compile(r'PostgreSQL (\d{1,2})\.(\d{1,2})\.?(\d{1,2})?')

# This DatabaseOperations class lives in here instead of base.py because it's

# used by both the 'postgresql' and 'postgresql_psycopg2' backends.

class DatabaseOperations(BaseDatabaseOperations):

    def __init__(self):

        self._postgres_version = None

    def _get_postgres_version(self):

        if self._postgres_version is None:

            from django.db import connection

            cursor = connection.cursor()

            cursor.execute("SELECT version()")

            version_string = cursor.fetchone()[0]

            m = server_version_re.match(version_string)

            if not m:

                raise Exception('Unable to determine PostgreSQL version from version() function string: %r' % version_string)

            self._postgres_version = [int(val) for val in m.groups() if val]

        return self._postgres_version

    postgres_version = property(_get_postgres_version)

    def date_extract_sql(self, lookup_type, field_name):

        # http://www.postgresql.org/docs/8.0/static/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT

        return "EXTRACT('%s' FROM %s)" % (lookup_type, field_name)

    def date_trunc_sql(self, lookup_type, field_name):

        # http://www.postgresql.org/docs/8.0/static/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC

        return "DATE_TRUNC('%s', %s)" % (lookup_type, field_name)

    def deferrable_sql(self):

        return " DEFERRABLE INITIALLY DEFERRED"

    def field_cast_sql(self, db_type):

        if db_type == 'inet':

            return 'HOST(%s)'

        return '%s'

    def last_insert_id(self, cursor, table_name, pk_name):

        cursor.execute("SELECT CURRVAL('\"%s_%s_seq\"')" % (table_name, pk_name))

        return cursor.fetchone()[0]

    def no_limit_value(self):

        return None

    def quote_name(self, name):

        if name.startswith('"') and name.endswith('"'):

            return name # Quoting once is enough.

        return '"%s"' % name

    def sql_flush(self, style, tables, sequences):

        if tables:

            if self.postgres_version[0] >= 8 and self.postgres_version[1] >= 1:

                # Postgres 8.1+ can do 'TRUNCATE x, y, z...;'. In fact, it *has to*

                # in order to be able to truncate tables referenced by a foreign

                # key in any other table. The result is a single SQL TRUNCATE

                # statement.

                sql = ['%s %s;' % \

                    (style.SQL_KEYWORD('TRUNCATE'),

                     style.SQL_FIELD(', '.join([self.quote_name(table) for table in tables]))

                )]

            else:

                # Older versions of Postgres can't do TRUNCATE in a single call, so

                # they must use a simple delete.

                sql = ['%s %s %s;' % \

                        (style.SQL_KEYWORD('DELETE'),

                         style.SQL_KEYWORD('FROM'),

                         style.SQL_FIELD(self.quote_name(table))

                         ) for table in tables]

            # 'ALTER SEQUENCE sequence_name RESTART WITH 1;'... style SQL statements

            # to reset sequence indices

            for sequence_info in sequences:

                table_name = sequence_info['table']

                column_name = sequence_info['column']

                if column_name and len(column_name) > 0:

                    sequence_name = '%s_%s_seq' % (table_name, column_name)

                else:

                    sequence_name = '%s_id_seq' % table_name

                sql.append("%s setval('%s', 1, false);" % \

                    (style.SQL_KEYWORD('SELECT'),

                    style.SQL_FIELD(self.quote_name(sequence_name)))

                )

            return sql

        else:

            return []

    def sequence_reset_sql(self, style, model_list):

        from django.db import models

        output = []

        qn = self.quote_name

        for model in model_list:

            # Use `coalesce` to set the sequence for each model to the max pk value if there are records,

            # or 1 if there are none. Set the `is_called` property (the third argument to `setval`) to true

            # if there are records (as the max pk value is already in use), otherwise set it to false.

            for f in model._meta.fields:

                if isinstance(f, models.AutoField):

                    output.append("%s setval('%s', coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \

                        (style.SQL_KEYWORD('SELECT'),

                        style.SQL_FIELD(qn('%s_%s_seq' % (model._meta.db_table, f.column))),

                        style.SQL_FIELD(qn(f.column)),

                        style.SQL_FIELD(qn(f.column)),

                        style.SQL_KEYWORD('IS NOT'),

                        style.SQL_KEYWORD('FROM'),

                        style.SQL_TABLE(qn(model._meta.db_table))))

                    break # Only one AutoField is allowed per model, so don't bother continuing.

            for f in model._meta.many_to_many:

                output.append("%s setval('%s', coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \

                    (style.SQL_KEYWORD('SELECT'),

                    style.SQL_FIELD(qn('%s_id_seq' % f.m2m_db_table())),

                    style.SQL_FIELD(qn('id')),

                    style.SQL_FIELD(qn('id')),

                    style.SQL_KEYWORD('IS NOT'),

                    style.SQL_KEYWORD('FROM'),

                    style.SQL_TABLE(qn(f.m2m_db_table()))))

        return output