require "study_engine/config"

module StudyEngine
  class Report < Struct.new(:assessments, :field, :direction)
    def self.event_fields
      StudyEngine.events.map.with_index { |_, index| :"event_#{index}" }
    end

    def self.group_class
      Struct.new(:study_id, *event_fields) do
        def each(&block)
          Report.event_fields.map { |field| send(field) }.each(&block)
        end

        def max_count
          Report.event_fields.map { |field| send(field).count }.max
        end

        def == other
          values == other.values
        end
      end
    end

    def groups
      sort build_groups
    end

    def build_groups
      assessments.reduce({}) do |groups, assessment|
        group = groups[assessment.study_id.to_s] || new_empty_group(assessment.study_id)

        field = field_map[assessment.event]

        group.send(field).push assessment
        group.send(field).sort_by! { |a| a.completed_at ? -1 : 1 }

        groups.merge(assessment.study_id.to_s => group)
      end.values
    end

    def sort groups
      groups.sort do |a, b|
        a = a.send(field)
        b = b.send(field)
        ascending? ? a <=> b : b <=> a
      end
    end

    def ascending?
      direction == "ASC"
    end

    private

    def field_map
      StudyEngine.events.inject({}) do |hash, event|
        index = StudyEngine.events.index(event)
        hash.merge event => "event_#{index}"
      end
    end

    def new_empty_group(study_id)
      empty_groups = StudyEngine.events.map { |_| [] }
      self.class.group_class.new(study_id, *empty_groups)
    end
  end
end