# encoding: UTF-8

module DryCrud
  # Sort functionality for the index table.
  # Define a default sort expression that is always appended to the
  # current sort params with the class attribute +default_sort+.
  module Sortable
    extend ActiveSupport::Concern

    included do
      class_attribute :sort_mappings_with_indifferent_access
      self.sort_mappings = {}

      class_attribute :default_sort

      helper_method :sortable?

      alias_method_chain :list_entries, :sort
    end

    # Class methods for sorting.
    module ClassMethods
      # Define a map of (virtual) attributes to SQL order expressions.
      # May be used for sorting table columns that do not appear directly
      # in the database table. E.g., map city_id: 'cities.name' to
      # sort the displayed city names.
      def sort_mappings=(hash)
        self.sort_mappings_with_indifferent_access =
          hash.with_indifferent_access
      end
    end

    private

    # Enhance the list entries with an optional sort order.
    def list_entries_with_sort
      sortable = sortable?(params[:sort])
      if sortable || default_sort
        clause = [sortable ? sort_expression : nil, default_sort]
        list_entries_without_sort.reorder(clause.compact.join(', '))
      else
        list_entries_without_sort
      end
    end

    # Return the sort expression to be used in the list query.
    def sort_expression
      col = sort_mappings_with_indifferent_access[params[:sort]] ||
            "#{model_class.table_name}.#{params[:sort]}"
      "#{col} #{sort_dir}"
    end

    # The sort direction, either 'asc' or 'desc'.
    def sort_dir
      params[:sort_dir] == 'desc' ? 'DESC' : 'ASC'
    end

    # Returns true if the passed attribute is sortable.
    def sortable?(attr)
      attr.present? && (
      model_class.column_names.include?(attr.to_s) ||
      sort_mappings_with_indifferent_access.include?(attr))
    end
  end
end