# encoding: utf-8
module Mongoid
  class Criteria
    module Queryable

      # Represents an aggregation pipeline.
      #
      # @since 2.0.0
      class Pipeline < Array

        # @attribute [r] aliases The field aliases.
        attr_reader :aliases

        # Deep copy the aggregation pipeline. Will clone all the values in the
        # pipeline as well as the pipeline itself.
        #
        # @example Deep copy the pipeline.
        #   pipeline.__deep_copy__
        #
        # @return [ Pipeline ] The cloned pipeline.
        #
        # @since 2.0.0
        def __deep_copy__
          self.class.new(aliases) do |copy|
            each do |entry|
              copy.push(entry.__deep_copy__)
            end
          end
        end

        # Add a group operation to the aggregation pipeline.
        #
        # @example Add a group operation.
        #   pipeline.group(:count.sum => 1, :max.max => "likes")
        #
        # @param [ Hash ] entry The group entry.
        #
        # @return [ Pipeline ] The pipeline.
        #
        # @since 2.0.0
        def group(entry)
          push("$group" => evolve(entry.__expand_complex__))
        end

        # Initialize the new pipeline.
        #
        # @example Initialize the new pipeline.
        #   Queryable::Pipeline.new(aliases)
        #
        # @param [ Hash ] aliases A hash of mappings from aliases to the actual
        #   field names in the database.
        #
        # @since 2.0.0
        def initialize(aliases = {})
          @aliases = aliases
          yield(self) if block_given?
        end

        # Adds a $project entry to the aggregation pipeline.
        #
        # @example Add the projection.
        #   pipeline.project(name: 1)
        #
        # @param [ Hash ] entry The projection.
        #
        # @return [ Pipeline ] The pipeline.
        def project(entry)
          push("$project" => evolve(entry))
        end

        # Add the $unwind entry to the pipeline.
        #
        # @example Add the unwind.
        #   pipeline.unwind(:field)
        #   pipeline.unwind(document)
        #
        # @param [ String, Symbol, Hash ] field_or_doc The name of the field or a document.
        #
        # @return [ Pipeline ] The pipeline.
        #
        # @since 2.0.0
        def unwind(field_or_doc)
          unless field_or_doc.respond_to? :keys
            normalized = field_or_doc.to_s
            name = aliases[normalized] || normalized
            push("$unwind" => name.__mongo_expression__)
          else
            push("$unwind" => field_or_doc)
          end
        end

        private

        # Evolve the entry using the aliases.
        #
        # @api private
        #
        # @example Evolve the entry.
        #   pipeline.evolve(name: 1)
        #
        # @param [ Hash ] entry The entry to evolve.
        #
        # @return [ Hash ] The evolved entry.
        #
        # @since 2.0.0
        def evolve(entry)
          aggregate = Selector.new(aliases)
          entry.each_pair do |field, value|
            aggregate.merge!(field.to_s => value)
          end
          aggregate
        end
      end
    end
  end
end