"""
MySQL database backend for Django.

Requires mysqlclient: https://pypi.org/project/mysqlclient/
"""
from django.core.exceptions import ImproperlyConfigured
from django.db import IntegrityError
from django.db.backends import utils as backend_utils
from django.db.backends.base.base import BaseDatabaseWrapper
from django.utils.asyncio import async_unsafe
from django.utils.functional import cached_property
from django.utils.regex_helper import _lazy_re_compile

try:
    import MySQLdb as Database
except ImportError as err:
    raise ImproperlyConfigured(
        'Error loading MySQLdb module.\n'
        'Did you install mysqlclient?'
    ) from err

from MySQLdb.constants import CLIENT, FIELD_TYPE
from MySQLdb.converters import conversions

# Some of these import MySQLdb, so import them after checking if it's installed.
from .client import DatabaseClient
from .creation import DatabaseCreation
from .features import DatabaseFeatures
from .introspection import DatabaseIntrospection
from .operations import DatabaseOperations
from .schema import DatabaseSchemaEditor
from .validation import DatabaseValidation

version = Database.version_info
if version < (1, 4, 0):
    raise ImproperlyConfigured('mysqlclient 1.4.0 or newer is required; you have %s.' % Database.__version__)


# MySQLdb returns TIME columns as timedelta -- they are more like timedelta in
# terms of actual behavior as they are signed and include days -- and Django
# expects time.
django_conversions = {
    **conversions,
    **{FIELD_TYPE.TIME: backend_utils.typecast_time},
}

# This should match the numerical portion of the version numbers (we can treat
# versions like 5.0.24 and 5.0.24a as the same).
server_version_re = _lazy_re_compile(r'(\d{1,2})\.(\d{1,2})\.(\d{1,2})')


class CursorWrapper:
    """
    A thin wrapper around MySQLdb's normal cursor class that catches particular
    exception instances and reraises them with the correct types.

    Implemented as a wrapper, rather than a subclass, so that it isn't stuck
    to the particular underlying representation returned by Connection.cursor().
    """
    codes_for_integrityerror = (
        1048,  # Column cannot be null
        1690,  # BIGINT UNSIGNED value is out of range
        3819,  # CHECK constraint is violated
        4025,  # CHECK constraint failed
    )

    def __init__(self, cursor):
        self.cursor = cursor

    def execute(self, query, args=None):
        try:
            # args is None means no string interpolation
            return self.cursor.execute(query, args)
        except Database.OperationalError as e:
            # Map some error codes to IntegrityError, since they seem to be
            # misclassified and Django would prefer the more logical place.
            if e.args[0] in self.codes_for_integrityerror:
                raise IntegrityError(*tuple(e.args))
            raise

    def executemany(self, query, args):
        try:
            return self.cursor.executemany(query, args)
        except Database.OperationalError as e:
            # Map some error codes to IntegrityError, since they seem to be
            # misclassified and Django would prefer the more logical place.
            if e.args[0] in self.codes_for_integrityerror:
                raise IntegrityError(*tuple(e.args))
            raise

    def __getattr__(self, attr):
        return getattr(self.cursor, attr)

    def __iter__(self):
        return iter(self.cursor)


class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'mysql'
    # This dictionary maps Field objects to their associated MySQL column
    # types, as strings. Column-type strings can contain format strings; they'll
    # be interpolated against the values of Field.__dict__ before being output.
    # If a column type is set to None, it won't be included in the output.
    data_types = {
        'AutoField': 'integer AUTO_INCREMENT',
        'BigAutoField': 'bigint AUTO_INCREMENT',
        'BinaryField': 'longblob',
        'BooleanField': 'bool',
        'CharField': 'varchar(%(max_length)s)',
        'DateField': 'date',
        'DateTimeField': 'datetime(6)',
        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
        'DurationField': 'bigint',
        'FileField': 'varchar(%(max_length)s)',
        'FilePathField': 'varchar(%(max_length)s)',
        'FloatField': 'double precision',
        'IntegerField': 'integer',
        'BigIntegerField': 'bigint',
        'IPAddressField': 'char(15)',
        'GenericIPAddressField': 'char(39)',
        'JSONField': 'json',
        'NullBooleanField': 'bool',
        'OneToOneField': 'integer',
        'PositiveBigIntegerField': 'bigint UNSIGNED',
        'PositiveIntegerField': 'integer UNSIGNED',
        'PositiveSmallIntegerField': 'smallint UNSIGNED',
        'SlugField': 'varchar(%(max_length)s)',
        'SmallAutoField': 'smallint AUTO_INCREMENT',
        'SmallIntegerField': 'smallint',
        'TextField': 'longtext',
        'TimeField': 'time(6)',
        'UUIDField': 'char(32)',
    }

    # For these data types:
    # - MySQL < 8.0.13 and MariaDB < 10.2.1 don't accept default values and
    #   implicitly treat them as nullable
    # - all versions of MySQL and MariaDB don't support full width database
    #   indexes
    _limited_data_types = (
        'tinyblob', 'blob', 'mediumblob', 'longblob', 'tinytext', 'text',
        'mediumtext', 'longtext', 'json',
    )

    operators = {
        'exact': '= %s',
        'iexact': 'LIKE %s',
        'contains': 'LIKE BINARY %s',
        'icontains': 'LIKE %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE BINARY %s',
        'endswith': 'LIKE BINARY %s',
        'istartswith': 'LIKE %s',
        'iendswith': 'LIKE %s',
    }

    # 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': "LIKE BINARY CONCAT('%%', {}, '%%')",
        'icontains': "LIKE CONCAT('%%', {}, '%%')",
        'startswith': "LIKE BINARY CONCAT({}, '%%')",
        'istartswith': "LIKE CONCAT({}, '%%')",
        'endswith': "LIKE BINARY CONCAT('%%', {})",
        'iendswith': "LIKE CONCAT('%%', {})",
    }

    isolation_levels = {
        'read uncommitted',
        'read committed',
        'repeatable read',
        'serializable',
    }

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

    def get_connection_params(self):
        kwargs = {
            'conv': django_conversions,
            'charset': 'utf8',
        }
        settings_dict = self.settings_dict
        if settings_dict['USER']:
            kwargs['user'] = settings_dict['USER']
        if settings_dict['NAME']:
            kwargs['database'] = settings_dict['NAME']
        if settings_dict['PASSWORD']:
            kwargs['password'] = settings_dict['PASSWORD']
        if settings_dict['HOST'].startswith('/'):
            kwargs['unix_socket'] = settings_dict['HOST']
        elif settings_dict['HOST']:
            kwargs['host'] = settings_dict['HOST']
        if settings_dict['PORT']:
            kwargs['port'] = int(settings_dict['PORT'])
        # We need the number of potentially affected rows after an
        # "UPDATE", not the number of changed rows.
        kwargs['client_flag'] = CLIENT.FOUND_ROWS
        # Validate the transaction isolation level, if specified.
        options = settings_dict['OPTIONS'].copy()
        isolation_level = options.pop('isolation_level', 'read committed')
        if isolation_level:
            isolation_level = isolation_level.lower()
            if isolation_level not in self.isolation_levels:
                raise ImproperlyConfigured(
                    "Invalid transaction isolation level '%s' specified.\n"
                    "Use one of %s, or None." % (
                        isolation_level,
                        ', '.join("'%s'" % s for s in sorted(self.isolation_levels))
                    ))
        self.isolation_level = isolation_level
        kwargs.update(options)
        return kwargs

    @async_unsafe
    def get_new_connection(self, conn_params):
        connection = Database.connect(**conn_params)
        # bytes encoder in mysqlclient doesn't work and was added only to
        # prevent KeyErrors in Django < 2.0. We can remove this workaround when
        # mysqlclient 2.1 becomes the minimal mysqlclient supported by Django.
        # See https://github.com/PyMySQL/mysqlclient/issues/489
        if connection.encoders.get(bytes) is bytes:
            connection.encoders.pop(bytes)
        return connection

    def init_connection_state(self):
        assignments = []
        if self.features.is_sql_auto_is_null_enabled:
            # SQL_AUTO_IS_NULL controls whether an AUTO_INCREMENT column on
            # a recently inserted row will return when the field is tested
            # for NULL. Disabling this brings this aspect of MySQL in line
            # with SQL standards.
            assignments.append('SET SQL_AUTO_IS_NULL = 0')

        if self.isolation_level:
            assignments.append('SET SESSION TRANSACTION ISOLATION LEVEL %s' % self.isolation_level.upper())

        if assignments:
            with self.cursor() as cursor:
                cursor.execute('; '.join(assignments))

    @async_unsafe
    def create_cursor(self, name=None):
        cursor = self.connection.cursor()
        return CursorWrapper(cursor)

    def _rollback(self):
        try:
            BaseDatabaseWrapper._rollback(self)
        except Database.NotSupportedError:
            pass

    def _set_autocommit(self, autocommit):
        with self.wrap_database_errors:
            self.connection.autocommit(autocommit)

    def disable_constraint_checking(self):
        """
        Disable foreign key checks, primarily for use in adding rows with
        forward references. Always return True to indicate constraint checks
        need to be re-enabled.
        """
        with self.cursor() as cursor:
            cursor.execute('SET foreign_key_checks=0')
        return True

    def enable_constraint_checking(self):
        """
        Re-enable foreign key checks after they have been disabled.
        """
        # Override needs_rollback in case constraint_checks_disabled is
        # nested inside transaction.atomic.
        self.needs_rollback, needs_rollback = False, self.needs_rollback
        try:
            with self.cursor() as cursor:
                cursor.execute('SET foreign_key_checks=1')
        finally:
            self.needs_rollback = needs_rollback

    def check_constraints(self, table_names=None):
        """
        Check each table name in `table_names` for rows with invalid foreign
        key references. This method is intended to be used in conjunction with
        `disable_constraint_checking()` and `enable_constraint_checking()`, to
        determine if rows with invalid references were entered while constraint
        checks were off.
        """
        with self.cursor() as cursor:
            if table_names is None:
                table_names = self.introspection.table_names(cursor)
            for table_name in table_names:
                primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
                if not primary_key_column_name:
                    continue
                key_columns = self.introspection.get_key_columns(cursor, table_name)
                for column_name, referenced_table_name, referenced_column_name in key_columns:
                    cursor.execute(
                        """
                        SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
                        LEFT JOIN `%s` as REFERRED
                        ON (REFERRING.`%s` = REFERRED.`%s`)
                        WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
                        """ % (
                            primary_key_column_name, column_name, table_name,
                            referenced_table_name, column_name, referenced_column_name,
                            column_name, referenced_column_name,
                        )
                    )
                    for bad_row in cursor.fetchall():
                        raise IntegrityError(
                            "The row in table '%s' with primary key '%s' has an invalid "
                            "foreign key: %s.%s contains a value '%s' that does not "
                            "have a corresponding value in %s.%s."
                            % (
                                table_name, bad_row[0], table_name, column_name,
                                bad_row[1], referenced_table_name, referenced_column_name,
                            )
                        )

    def is_usable(self):
        try:
            self.connection.ping()
        except Database.Error:
            return False
        else:
            return True

    @cached_property
    def display_name(self):
        return 'MariaDB' if self.mysql_is_mariadb else 'MySQL'

    @cached_property
    def data_type_check_constraints(self):
        if self.features.supports_column_check_constraints:
            check_constraints = {
                'PositiveBigIntegerField': '`%(column)s` >= 0',
                'PositiveIntegerField': '`%(column)s` >= 0',
                'PositiveSmallIntegerField': '`%(column)s` >= 0',
            }
            if self.mysql_is_mariadb and self.mysql_version < (10, 4, 3):
                # MariaDB < 10.4.3 doesn't automatically use the JSON_VALID as
                # a check constraint.
                check_constraints['JSONField'] = 'JSON_VALID(`%(column)s`)'
            return check_constraints
        return {}

    @cached_property
    def mysql_server_data(self):
        with self.temporary_connection() as cursor:
            # Select some server variables and test if the time zone
            # definitions are installed. CONVERT_TZ returns NULL if 'UTC'
            # timezone isn't loaded into the mysql.time_zone table.
            cursor.execute("""
                SELECT VERSION(),
                       @@sql_mode,
                       @@default_storage_engine,
                       @@sql_auto_is_null,
                       @@lower_case_table_names,
                       CONVERT_TZ('2001-01-01 01:00:00', 'UTC', 'UTC') IS NOT NULL
            """)
            row = cursor.fetchone()
        return {
            'version': row[0],
            'sql_mode': row[1],
            'default_storage_engine': row[2],
            'sql_auto_is_null': bool(row[3]),
            'lower_case_table_names': bool(row[4]),
            'has_zoneinfo_database': bool(row[5]),
        }

    @cached_property
    def mysql_server_info(self):
        return self.mysql_server_data['version']

    @cached_property
    def mysql_version(self):
        match = server_version_re.match(self.mysql_server_info)
        if not match:
            raise Exception('Unable to determine MySQL version from version string %r' % self.mysql_server_info)
        return tuple(int(x) for x in match.groups())

    @cached_property
    def mysql_is_mariadb(self):
        return 'mariadb' in self.mysql_server_info.lower()

    @cached_property
    def sql_mode(self):
        sql_mode = self.mysql_server_data['sql_mode']
        return set(sql_mode.split(',') if sql_mode else ())
