class ActiveRecord::ConnectionAdapters::MySQL::SchemaCreation

def add_column_options!(sql, options)
  # By default, TIMESTAMP columns are NOT NULL, cannot contain NULL values,
  # and assigning NULL assigns the current timestamp. To permit a TIMESTAMP
  # column to contain NULL, explicitly declare it with the NULL attribute.
  # See https://dev.mysql.com/doc/refman/en/timestamp-initialization.html
  if /\Atimestamp\b/.match?(options[:column].sql_type) && !options[:primary_key]
    sql << " NULL" unless options[:null] == false || options_include_default?(options)
  end
  if charset = options[:charset]
    sql << " CHARACTER SET #{charset}"
  end
  if collation = options[:collation]
    sql << " COLLATE #{collation}"
  end
  if as = options[:as]
    sql << " AS (#{as})"
    if options[:stored]
      sql << (mariadb? ? " PERSISTENT" : " STORED")
    end
  end
  add_sql_comment!(super, options[:comment])
end

def add_column_position!(sql, options)
  if options[:first]
    sql << " FIRST"
  elsif options[:after]
    sql << " AFTER #{quote_column_name(options[:after])}"
  end
  sql
end

def add_table_options!(create_sql, o)
  create_sql << " DEFAULT CHARSET=#{o.charset}" if o.charset
  create_sql << " COLLATE=#{o.collation}" if o.collation
  add_sql_comment!(super, o.comment)
end

def index_in_create(table_name, column_name, options)
  index, _ = @conn.add_index_options(table_name, column_name, **options)
  accept(index)
end

def visit_AddColumnDefinition(o)
  add_column_position!(super, column_options(o.column))
end

def visit_ChangeColumnDefaultDefinition(o)
  sql = +"ALTER COLUMN #{quote_column_name(o.column.name)} "
  if o.default.nil? && !o.column.null
    sql << "DROP DEFAULT"
  else
    sql << "SET DEFAULT #{quote_default_expression(o.default, o.column)}"
  end
end

def visit_ChangeColumnDefinition(o)
  change_column_sql = +"CHANGE #{quote_column_name(o.name)} #{accept(o.column)}"
  add_column_position!(change_column_sql, column_options(o.column))
end

def visit_CreateIndexDefinition(o)
  sql = visit_IndexDefinition(o.index, true)
  sql << " #{o.algorithm}" if o.algorithm
  sql
end

def visit_DropCheckConstraint(name)
  "DROP #{mariadb? ? 'CONSTRAINT' : 'CHECK'} #{name}"
end

def visit_DropForeignKey(name)
  "DROP FOREIGN KEY #{name}"
end

def visit_IndexDefinition(o, create = false)
  index_type = o.type&.to_s&.upcase || o.unique && "UNIQUE"
  sql = create ? ["CREATE"] : []
  sql << index_type if index_type
  sql << "INDEX"
  sql << quote_column_name(o.name)
  sql << "USING #{o.using}" if o.using
  sql << "ON #{quote_table_name(o.table)}" if create
  sql << "(#{quoted_columns(o)})"
  add_sql_comment!(sql.join(" "), o.comment)
end