"""
SQLite3 backend for the sqlite3 module in the standard library.
"""
import decimal
import re
import warnings
from sqlite3 import dbapi2 as Database

import pytz

from django.core.exceptions import ImproperlyConfigured
from django.db import utils
from django.db.backends import utils as backend_utils
from django.db.backends.base.base import BaseDatabaseWrapper
from django.utils import timezone
from django.utils.dateparse import (
    parse_date, parse_datetime, parse_duration, parse_time,
)

from .client import DatabaseClient                          # isort:skip
from .creation import DatabaseCreation                      # isort:skip
from .features import DatabaseFeatures                      # isort:skip
from .introspection import DatabaseIntrospection            # isort:skip
from .operations import DatabaseOperations                  # isort:skip
from .schema import DatabaseSchemaEditor                    # isort:skip


def decoder(conv_func):
    """
    Convert bytestrings from Python's sqlite3 interface to a regular string.
    """
    return lambda s: conv_func(s.decode())


Database.register_converter("bool", decoder(lambda s: s == '1'))
Database.register_converter("time", decoder(parse_time))
Database.register_converter("date", decoder(parse_date))
Database.register_converter("datetime", decoder(parse_datetime))
Database.register_converter("timestamp", decoder(parse_datetime))
Database.register_converter("TIMESTAMP", decoder(parse_datetime))
Database.register_converter("decimal", decoder(backend_utils.typecast_
decimal))

Database.register_adapter(decimal.Decimal, backend_utils.rev_typecast_decimal)


class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'sqlite'
    display_name = 'SQLite'
    # SQLite doesn't 
actually support most of these types, but it "does the right
    # thing" given more verbose field definitions, so leave them as is so that
    # schema inspection is more useful.
    data_types = {
        'AutoField': 'integer',
        'BigAutoField': 'integer',
        'BinaryField': 'BLOB',
        'BooleanField': 'bool',
        'CharField': 'varchar(%(max_length)s)',
        'DateField': 'date',
        'DateTimeField': 'datetime',
        'DecimalField': 'decimal',
        'DurationField': 'bigint',
        'FileField': 'varchar(%(max_length)s)',
        'FilePathField': 'varchar(%(max_length)s)',
        'FloatField': 'real',
        'IntegerField': 'integer',
        'BigIntegerField': 'bigint',
        'IPAddressField': 'char(15)',
        'GenericIPAddressField': 'char(39)',
        'NullBooleanField': 'bool',
        'OneToOneField': 'integer',
        'PositiveIntegerField': 'integer unsigned',
        'PositiveSmallIntegerField': 'smallint unsigned',
        'SlugField': 'varchar(%(max_length)s)',
        'SmallIntegerField': 'smallint',
        'TextField': 'text',
        'TimeField': 'time',
        'UUIDField': 'char(32)',
    }
    data_types_suffix = {
        'AutoField': 'AUTOINCREMENT',
        'BigAutoField': 'AUTOINCREMENT',
    }
    # SQLite requires LIKE statements to include an ESCAPE clause if the value
    # being escaped has a percent or underscore in it.
    # See http://www.sqlite.org/lang_expr.html for an explanation.
    operators = {
        'exact': '= %s',
        'iexact': "LIKE %s ESCAPE '\\'",
        'contains': "LIKE %s ESCAPE '\\'",
        'icontains': "LIKE %s ESCAPE '\\'",
        'regex': 'REGEXP %s',
        'iregex': "REGEXP '(?i)' || %s",
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': "LIKE %s ESCAPE '\\'",
        'endswith': "LIKE %s ESCAPE '\\'",
        'istartswith': "LIKE %s ESCAPE '\\'",
        'iendswith': "LIKE %s ESCAPE '\\'",
    }

    # The patterns below are used to generate SQL pattern lookup clauses when
    # the right-hand side of the lookup isn't a raw string (it might be an expression
    # or the result of a bilateral transformation).
    # In those cases, special characters for LIKE operators (e.g. \, *, _) should be
    # escaped on database side.
    #
    # Note: we use str.format() here for readability as '%' is used as a wildcard for
    # the LIKE operator.
    pattern_esc = r"REPLACE(REPLACE(REPLACE({}, '\', '\\'), '%%', '\%%'), '_', '\_')"
    pattern_ops = {
        'contains': r"LIKE '%%' || {} || '%%' ESCAPE '\'",
        'icontains': r"LIKE '%%' || UPPER({}) || '%%' ESCAPE '\'",
        'startswith': r"LIKE {} || '%%' ESCAPE '\'",
        'istartswith': r"LIKE UPPER({}) || '%%' ESCAPE '\'",
        'endswith': r"LIKE '%%' || {} ESCAPE '\'",
        'iendswith': r"LIKE '%%' || UPPER({}) ESCAPE '\'",
    }

    Database = Database
    SchemaEditorClass = DatabaseSchemaEditor
    # Classes instantiated in __init__().
    client_class = DatabaseClient
    creation_class = DatabaseCreation
    features_class = DatabaseFeatures
    introspection_class = DatabaseIntrospection
    ops_class = DatabaseOperations

    def get_connection_params(self):
        settings_dict = self.settings_dict
        if not settings_dict['NAME']:
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        kwargs = {
            'database': settings_dict['NAME'],
            'detect_types': Database.PARSE_DECLTYPES | Database.PARSE_COLNAMES,
        }
        kwargs.update(settings_dict['OPTIONS'])
        # Always allow the underlying SQLite connection to be shareable
        # between multiple threads. The safe-guarding will be handled at a
        # higher level by the `BaseDatabaseWrapper.allow_thread_sharing`
        # property. This is necessary as the shareability is disabled by
        # default in pysqlite and it cannot be changed once a connection is
        # opened.
        if 'check_same_thread' in kwargs and kwargs['check_same_thread']:
            warnings.warn(
                'The `check_same_thread` option was provided and set to '
                'True. It will be overridden with False. Use the '
                '`DatabaseWrapper.allow_thread_sharing` property instead '
                'for controlling thread shareability.',
                RuntimeWarning
            )
        kwargs.update({'check_same_thread': False})
        if self.features.can_share_in_memory_db:
            kwargs.update({'uri': True})
        return kwargs

    def get_new_connection(self, conn_params):
        conn = Database.connect(**conn_params)
        conn.create_function("django_date_extract", 2, _sqlite_date_extract)
        conn.create_function("django_date_trunc", 2, _sqlite_date_trunc)
        conn.create_function("django_datetime_cast_date", 2, _sqlite_datetime_cast_date)
        conn.create_function("django_datetime_cast_time", 2, _sqlite_datetime_cast_time)
        conn.create_function("django_datetime_extract", 3, _sqlite_datetime_extract)
        conn.create_function("django_datetime_trunc", 3, _sqlite_datetime_trunc)
        conn.create_function("django_time_extract", 2, _sqlite_time_extract)
        conn.create_function("django_time_trunc", 2, _sqlite_time_trunc)
        conn.create_function("django_time_diff", 2, _sqlite_time_diff)
        conn.create_function("django_timestamp_diff", 2, _sqlite_timestamp_diff)
        conn.create_function("regexp", 2, _sqlite_regexp)
        conn.create_function("django_format_dtdelta", 3, _sqlite_format_dtdelta)
        conn.create_function("django_power", 2, _sqlite_power)
        return conn

    def init_connection_state(self):
        pass

    def create_cursor(self, name=None):
        return self.connection.cursor(factory=SQLiteCursorWrapper)

    def close(self):
        self.validate_thread_sharing()
        # If database is in memory, closing the connection destroys the
        # database. To prevent accidental data loss, ignore close requests on
        # an in-memory db.
        if not self.is_in_memory_db():
            BaseDatabaseWrapper.close(self)

    def _savepoint_allowed(self):
        # Two conditions are required here:
        # - A sufficiently recent version of SQLite to support savepoints,
        # - Being in