class ActiveRecord::Generators::MigrationGenerator

def attributes_with_index
  attributes.select { |a| !a.reference? && a.has_index? }
end

def create_migration_file
  set_local_assigns!
  validate_file_name!
  migration_template @migration_template, File.join(db_migrate_path, "#{file_name}.rb")
end

def index_name_for(attribute)
  if attribute.foreign_key?
    attribute.name
  else
    attribute.name.singularize.foreign_key
  end.to_sym
end

def normalize_table_name(_table_name)
  pluralize_table_names? ? _table_name.pluralize : _table_name.singularize
end

def set_index_names
  attributes.each_with_index do |attr, i|
    attr.index_name = [attr, attributes[i - 1]].map { |a| index_name_for(a) }
  end
end

def set_local_assigns!
  @migration_template = "migration.rb"
  case file_name
  when /^(add)_.*_to_(.*)/, /^(remove)_.*?_from_(.*)/
    @migration_action = $1
    @table_name       = normalize_table_name($2)
  when /join_table/
    if attributes.length == 2
      @migration_action = "join"
      @join_tables      = pluralize_table_names? ? attributes.map(&:plural_name) : attributes.map(&:singular_name)
      set_index_names
    end
  when /^create_(.+)/
    @table_name = normalize_table_name($1)
    @migration_template = "create_table_migration.rb"
  end
end

def validate_file_name!
  unless /^[_a-z0-9]+$/.match?(file_name)
    raise IllegalMigrationNameError.new(file_name)
  end
end