import uuid

from django.conf import settings
from django.db.backends.base.operations import BaseDatabaseOperations
from django.utils import timezone
from django.utils.encoding import force_text


class DatabaseOperations(BaseDatabaseOperations):
    compiler_module = "django.db.backends.mysql.compiler"

    # MySQL stores positive fields as UNSIGNED ints.
    integer_field_ranges = dict(
        BaseDatabaseOperations.integer_field_ranges,
        PositiveSmallIntegerField=(0, 65535),
        PositiveIntegerField=(0, 4294967295),
    )

    def date_extract_sql(self, lookup_type, field_name):
        # http://dev.mysql.com/doc/mysql/en/date-and-time-functions.html
        if lookup_type == 'week_day':
            # DAYOFWEEK() returns an integer, 1-7, Sunday=1.
            # Note: WEEKDAY() returns 0-6, Monday=0.
            return "DAYOFWEEK(%s)" % field_name
        elif lookup_type == 'week':
            # Override the value of default_week_format for consistency with
            # other database backends.
            # Mode 3: Monday, 1-53, with 4 or more days this year.
            return "WEEK(%s, 3)" % field_name
        else:
            # EXTRACT returns 1-53 based on ISO-8601 for the week number.
            return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)

    def date_trunc_sql(self, lookup_type, field_name):
        fields = {
            'year': '%%Y-01-01',
            'month': '%%Y-%%m-01',
        }  # Use double percents to escape.
        if lookup_type in fields:
            format_str = fields[lookup_type]
            return "CAST(DATE_FORMAT(%s, '%s') AS DATE)" % (field_name, format_str)
        else:
            return "DATE(%s)" % (field_name)

    def _convert_field_to_tz(self, field_name, tzname):
        if settings.USE_TZ:
            field_name = "CONVERT_TZ(%s, 'UTC', %%s)" % field_name
            params = [tzname]
        else:
            params = []
        return field_name, params

    def datetime_cast_date_sql(self, field_name, tzname):
        field_name, params = self._convert_field_to_tz(field_name, tzname)
        sql = "DATE(%s)" % field_name
        return sql, params

    def datetime_cast_time_sql(self, field_name, tzname):
        field_name, params = self._convert_field_to_tz(field_name, tzname)
        sql = "TIME(%s)" % field_name
        return sql, params

    def datetime_extract_sql(self, lookup_type, field_name, tzname):
        field_name, params = self._convert_field_to_tz(field_name, tzname)
        sql = self.date_extract_sql(lookup_type, field_name)
        return sql, params

    def datetime_trunc_sql(self, lookup_type, field_name, tzname):
        field_name, params = self._convert_field_to_tz(field_name, tzname)
        fields = ['year', 'month', 'day', 'hour', 'minute', 'second']
        format = ('%%Y-', '%%m', '-%%d', ' %%H:', '%%i', ':%%s')  # Use double percents to escape.
        format_def = ('0000-', '01', '-01', ' 00:', '00', ':00')
        try:
            i = fields.index(lookup_type) + 1
        except ValueError:
            sql = field_name
        else:
            format_str = ''.join([f for f in format[:i]] + [f for f in format_def[i:]])
            sql = "CAST(DATE_FORMAT(%s, '%s') AS DATETIME)" % (field_name, format_str)
        return sql, params

    def time_trunc_sql(self, lookup_type, field_name):
        fields = {
            'hour': '%%H:00:00',
            'minute': '%%H:%%i:00',
            'second': '%%H:%%i:%%s',
        }  # Use double percents to escape.
        if lookup_type in fields:
            format_str = fields[lookup_type]
            return "CAST(DATE_FORMAT(%s, '%s') AS TIME)" % (field_name, format_str)
        else:
            return "TIME(%s)" % (field_name)

    def date_interval_sql(self, timedelta):
        return "INTERVAL '%06f' SECOND_MICROSECOND" % (timedelta.total_seconds()), []

    def format_for_duration_arithmetic(self, sql):
        if self.connection.features.supports_microsecond_precision:
            return 'INTERVAL %s MICROSECOND' % sql
        else:
            return 'INTERVAL FLOOR(%s / 1000000) SECOND' % sql

    def force_no_ordering(self):
        """
        "ORDER BY NULL" prevents MySQL from implicitly ordering by grouped
        columns. If no ordering would otherwise be applied, we don't want any
        implicit sorting going on.
        """
        return [(None, ("NULL", [], False))]

    def last_executed_query(self, cursor, sql, params):
        # With MySQLdb, cursor objects have an (undocumented) "_last_executed"
        # attribute where the exact query sent to the database is saved.
        # See MySQLdb/cursors.py in the source distribution.
        return force_text(getattr(cursor, '_last_executed', None), errors='replace')

    def no_limit_value(self):
        # 2**64 - 1, as recommended by the MySQL documentation
        return 18446744073709551615

    def quote_name(self, name):
        if name.startswith("`") and name.endswith("`"):
            return name  # Quoting once is enough.
        return "`%s`" % name

    def random_function_sql(self):
        return 'RAND()'

    def sql_flush(self, style, tables, sequences, allow_cascade=False):
        # NB: The generated SQL below is specific to MySQL
        # 'TRUNCATE x;', 'TRUNCATE y;', 'TRUNCATE z;'... style SQL statements
        # to clear all tables of all data
        if tables:
            sql = ['SET FOREIGN_KEY_CHECKS = 0;']
            for table in tables:
                sql.append('%s %s;' % (
                    style.SQL_KEYWORD('TRUNCATE'),
                    style.SQL_FIELD(self.quote_name(table)),
                ))
            sql.append('SET FOREIGN_KEY_CHECKS = 1;')
            sql.extend(self.sequence_reset_by_name_sql(style, sequences))
            return sql
        else:
            return []

    def validate_autopk_value(self, value):
        # MySQLism: zero in AUTO_INCREMENT field does not work. Refs #17653.
        if value == 0:
            raise ValueError('The database backend does not accept 0 as a '
                             'value for AutoField.')
        return value

    def adapt_datetimefield_value(self, value):
        if value is None:
            return None

        # Expression values are adapted by the database.
        if hasattr(value, 'resolve_expression'):
            return value

        # MySQL doesn't support tz-aware datetimes
        if timezone.is_aware(value):
            if settings.USE_TZ:
                value = timezone.make_naive(value, self.connection.timezone)
            else:
                raise ValueError("MySQL backend does not support timezone-aware datetimes when USE_TZ is False.")

        if not self.connection.features.supports_microsecond_precision:
            value = value.replace(microsecond=0)

        return str(value)

    def adapt_timefield_value(self, value):
        if value is None:
            return None

        # Expression values are adapted by the database.
        if hasattr(value, 'resolve_expression'):
            return value

        # MySQL doesn't support tz-aware times
        if timezone.is_aware(value):
            raise ValueError("MySQL backend does not support timezone-aware times.")

        return str(value)

    def max_name_length(self):
        return 64

    def bulk_insert_sql(self, fields, placeholder_rows):
        placeholder_rows_sql = (", ".join(row) for row in placeholder_rows)
        values_sql = ", ".join("(%s)" % sql for sql in placeholder_rows_sql)
        return "VALUES " + values_sql

    def combine_expression(self, connector, sub_expressions):
        if connector == '^':
            return 'POW(%s)' % ','.join(sub_expressions)
        # Convert the result to a signed integer since MySQL's binary operators
        # return an unsigned integer.
        elif connector in ('&', '|', '<<'):
            return 'CONVERT(%s, SIGNED)' % connector.join(sub_expressions)
        elif connector == '>>':
            lhs, rhs = sub_expressions
            return 'FLOOR(%(lhs)s / POW(2, %(rhs)s))' % {'lhs': lhs, 'rhs': rhs}
        return super(DatabaseOperations, self).combine_expression(connector, sub_expressions)

    def get_db_converters(self, expression):
        converters = super(DatabaseOperations, self).get_db_converters(expression)
        internal_type = expression.output_field.get_internal_type()
        if internal_type == 'TextField':
            converters.append(self.convert_textfield_value)
        elif internal_type in ['BooleanField', 'NullBooleanField']:
            converters.append(self.convert_booleanfield_value)
        elif internal_type == 'DateTimeField':
            converters.append(self.convert_datetimefield_value)
        elif internal_type == 'UUIDField':
            converters.append(self.convert_uuidfield_value)
        return converters

    def convert_textfield_value(self, value, expression, connection, context):
        if value is not None:
            value = force_text(value)
        return value

    def convert_booleanfield_value(self, value, expression, connection, context):
        if value in (0, 1):
            value = bool(value)
        return value

    def convert_datetimefield_value(self, value, expression, connection, context):
        if value is not None:
            if settings.USE_TZ:
                value = timezone.make_aware(value, self.connection.timezone)
        return value

    def convert_uuidfield_value(self, value, expression, connection, context):
        if value is not None:
            value = uuid.UUID(value)
        return value

    def binary_placeholder_sql(self, value):
        return '_binary %s' if value is not None else '%s'

    def subtract_temporals(self, internal_type, lhs, rhs):
        lhs_sql, lhs_params = lhs
        rhs_sql, rhs_params = rhs
        if self.connection.features.supports_microsecond_precision:
            if internal_type == 'TimeField':
                return (
                    "((TIME_TO_SEC(%(lhs)s) * POW(10, 6) + MICROSECOND(%(lhs)s)) -"
                    " (TIME_TO_SEC(%(rhs)s) * POW(10, 6) + MICROSECOND(%(rhs)s)))"
                ) % {'lhs': lhs_sql, 'rhs': rhs_sql}, lhs_params * 2 + rhs_params * 2
            else:
                return "TIMESTAMPDIFF(MICROSECOND, %s, %s)" % (rhs_sql, lhs_sql), rhs_params + lhs_params
        elif internal_type == 'TimeField':
            return (
                "(TIME_TO_SEC(%s) * POW(10, 6) - TIME_TO_SEC(%s) * POW(10, 6))"
            ) % (lhs_sql, rhs_sql), lhs_params + rhs_params
        else:
            return "(TIMESTAMPDIFF(SECOND, %s, %s) * POW(10, 6))" % (rhs_sql, lhs_sql), rhs_params + lhs_params