# frozen_string_literal: true

module MrCommon
  # Imports PreRegistration records from a CSV file that looks like:
  #
  #   first_name, last_name, email
  #   John, Smith, jsmith@example.com
  #   Jane, Doe, jdoe@example.com
  #   ,,unknown@example.com
  #   Name,Only,
  #
  # @author Corey Smedstad <csmedstad@mreach.com>
  class PreRegistrationImporter
    RowStruct = Struct.new(:first_name, :last_name, :email) do
      # Returns true if the row does not represent a duplicate PreRegistration
      # @return [Boolean]
      def new?
        !PreRegistration.exists_for?(self)
      end
    end

    ResultStruct = Struct.new(:created, :skipped)

    attr_reader :csv, :current_row, :result

    # @param csv [String] a the contents of a CSV file
    def initialize(csv)
      @csv = csv
      @created = 0
      @skipped = 0
    end

    # Attempts to create PreRegistration records for each row in the CSV
    # recording the number of created and skipped records in the process.
    #
    # The result is memoized to prevent double imports.
    #
    # @returns [ResultStruct] the result of the import
    def import
      @result ||= perform_import
    end

    private

      def perform_import
        PreRegistration.transaction do
          rows.each do |data|
            load_row(data)

            if current_row.new?
              make_pre_registration
            else
              skip_pre_registration
            end
          end
        end

        ResultStruct.new(@created, @skipped)
      end

      def rows
        CSV.parse(csv, headers: true)
      end

      def load_row(data)
        first_name = data[0] || ""
        last_name = data[1] || ""
        email = data[2] || ""

        @current_row = RowStruct.new(first_name, last_name, email)
      end

      def make_pre_registration
        pre_registration = PreRegistration.new(
          first_name: current_row.first_name,
          last_name: current_row.last_name,
          email: current_row.email
        )

        if pre_registration.save
          @created += 1
        else
          skip_pre_registration
        end
      end

      def skip_pre_registration
        @skipped += 1
      end
  end
end