"""
MySQL database backend for Django.

Requires CyMySQL: https://github.com/nakagami/CyMySQL
"""
from __future__ import unicode_literals

import uuid

from django.conf import settings
try:
    from django.db.backends import BaseDatabaseOperations
except ImportError: # 1.8
    from django.db.backends.base.operations import BaseDatabaseOperations
from django.utils import six, 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.
    if hasattr(BaseDatabaseOperations, 'integer_field_ranges'):
        integer_field_ranges = dict(BaseDatabaseOperations.integer_field_ranges,
            PositiveSmallIntegerField=(0, 4294967295),
            PositiveIntegerField=(0, 18446744073709551615),
        )

    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
        else:
            return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)

    def date_trunc_sql(self, lookup_type, field_name):
        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

    def datetime_extract_sql(self, lookup_type, field_name, tzname):
        if settings.USE_TZ:
            field_name = "CONVERT_TZ(%s, 'UTC', %%s)" % field_name
            params = [tzname]
        else:
            params = []
        # 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.
            sql = "DAYOFWEEK(%s)" % field_name
        else:
            sql = "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)
        return sql, params

    def datetime_trunc_sql(self, lookup_type, field_name, tzname):
        if settings.USE_TZ:
            field_name = "CONVERT_TZ(%s, 'UTC', %%s)" % field_name
            params = [tzname]
        else:
            params = []
        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 date_interval_sql(self, *args):
        if len(args) == 3:
            sql, connector, timedelta = args[0], args[1], args[2]
            return "(%s %s INTERVAL '%d 0:0:%d:%d' DAY_MICROSECOND)" % (
                sql, connector,
                timedelta.days, timedelta.seconds, timedelta.microseconds)
        else:   # 1.8
            timedelta = args[0]
            return "INTERVAL '%d 0:0:%d:%d' DAY_MICROSECOND" % (
                timedelta.days, timedelta.seconds, timedelta.microseconds), []

    def format_for_duration_arithmetic(self, sql):
        return 'INTERVAL %s MICROSECOND' % sql

    def drop_foreignkey_sql(self):
        return "DROP FOREIGN KEY"

    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.
        """
        import django
        if django.VERSION[1] < 8:   # 1.6, 1.7
            return ["NULL"]
        else:    # 1.8
            return [(None, ("NULL", [], False))]

    def fulltext_search_sql(self, field_name):
        return 'MATCH (%s) AGAINST (%%s IN BOOLEAN MODE)' % field_name

    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 value_to_db_datetime(self, value):
        if value is None:
            return None

        # MySQL doesn't support tz-aware datetimes
        if timezone.is_aware(value):
            if settings.USE_TZ:
                value = value.astimezone(timezone.utc).replace(tzinfo=None)
            else:
                raise ValueError("MySQL backend does not support timezone-aware datetimes when USE_TZ is False.")

        # MySQL doesn't support microseconds
        return six.text_type(value.replace(microsecond=0))

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

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

        # MySQL doesn't support microseconds
        return six.text_type(value.replace(microsecond=0))

    def year_lookup_bounds_for_datetime_field(self, value):
        # Again, no microseconds
        first, second = super(DatabaseOperations, self).year_lookup_bounds_for_datetime_field(value)
        return [first.replace(microsecond=0), second.replace(microsecond=0)]

    def max_name_length(self):
        return 64

    def bulk_insert_sql(self, fields, num_values):
        items_sql = "(%s)" % ", ".join(["%s"] * len(fields))
        return "VALUES " + ", ".join([items_sql] * num_values)

    def combine_expression(self, connector, sub_expressions):
        """
        MySQL requires special cases for ^ operators in query expressions
        """
        if connector == '^':
            return 'POW(%s)' % ','.join(sub_expressions)
        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 in ['BooleanField', 'NullBooleanField']:
            converters.append(self.convert_booleanfield_value)
        if internal_type == 'UUIDField':
            converters.append(self.convert_uuidfield_value)
        if internal_type == 'TextField':
            converters.append(self.convert_textfield_value)
        return converters

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

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

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

