"""
   MySQL database specific implementations of changeset classes.
"""

from sqlalchemy.databases import mysql as sa_base

from migrate.changeset import ansisql, exceptions


MySQLSchemaGenerator = sa_base.MySQLSchemaGenerator


class MySQLColumnGenerator(MySQLSchemaGenerator, ansisql.ANSIColumnGenerator):
    pass


class MySQLColumnDropper(ansisql.ANSIColumnDropper):
    pass


class MySQLSchemaChanger(MySQLSchemaGenerator, ansisql.ANSISchemaChanger):

    def visit_column(self, column):
        delta = column.delta
        table = column.table
        colspec = self.get_column_specification(column)

        if not hasattr(delta, 'result_column'):
            # Mysql needs the whole column definition, not just a lone name/type
            raise exceptions.NotSupportedError(
                "A column object must be present in table to alter it")

        self.start_alter_table(table)

        old_col_name = self.preparer.quote(delta.current_name, column.quote)
        self.append("CHANGE COLUMN %s " % old_col_name)
        self.append(colspec)
        self.execute()

    def visit_index(self, param):
        # If MySQL can do this, I can't find how
        raise exceptions.NotSupportedError("MySQL cannot rename indexes")


class MySQLConstraintGenerator(ansisql.ANSIConstraintGenerator):
    pass


class MySQLConstraintDropper(ansisql.ANSIConstraintDropper):

    def visit_migrate_primary_key_constraint(self, constraint):
        self.start_alter_table(constraint)
        self.append("DROP PRIMARY KEY")
        self.execute()

    def visit_migrate_foreign_key_constraint(self, constraint):
        self.start_alter_table(constraint)
        self.append("DROP FOREIGN KEY ")
        constraint.name = self.get_constraint_name(constraint)
        self.append(self.preparer.format_constraint(constraint))
        self.execute()

    def visit_migrate_check_constraint(self, *p, **k):
        raise exceptions.NotSupportedError("MySQL does not support CHECK"
            " constraints, use triggers instead.")

    def visit_migrate_unique_constraint(self, constraint, *p, **k):
        self.start_alter_table(constraint)
        self.append('DROP INDEX ')
        constraint.name = self.get_constraint_name(constraint)
        self.append(self.preparer.format_constraint(constraint))
        self.execute()


class MySQLDialect(ansisql.ANSIDialect):
    columngenerator = MySQLColumnGenerator
    columndropper = MySQLColumnDropper
    schemachanger = MySQLSchemaChanger
    constraintgenerator = MySQLConstraintGenerator
    constraintdropper = MySQLConstraintDropper