# frozen_string_literal: true

# A single history list; this is a more intelligent wrapper around the basic
# Innodb::List::History which is provided elsewhere.
module Innodb
  class HistoryList
    attr_reader :list

    # Initialize from a provided Innodb::List::History.
    def initialize(list)
      @list = list
    end

    class UndoRecordCursor
      def initialize(history, undo_record, direction = :forward)
        @history = history
        @undo_record = undo_record

        # rubocop:disable Style/IfUnlessModifier
        case undo_record
        when :min
          @undo_log_cursor = history.list.list_cursor(:min, direction)
          if (@undo_log = @undo_log_cursor.node)
            @undo_record_cursor = @undo_log.undo_record_cursor(:min, direction)
          end
        when :max
          @undo_log_cursor = history.list.list_cursor(:max, direction)
          if (@undo_log = @undo_log_cursor.node)
            @undo_record_cursor = @undo_log.undo_record_cursor(:max, direction)
          end
        else
          raise "Not implemented"
        end
        # rubocop:enable Style/IfUnlessModifier
      end

      def undo_record
        return nil unless @undo_record_cursor

        if (rec = @undo_record_cursor.undo_record)
          return rec
        end

        case @direction
        when :forward
          next_undo_record
        when :backward
          prev_undo_record
        end
      end

      def move_cursor(page, undo_record)
        @undo_log = page
        @undo_log_cursor = @undo_log.undo_record_cursor(undo_record, @direction)
      end

      def next_undo_record
        if (rec = @undo_record_cursor.undo_record)
          return rec
        end

        if (undo_log = @undo_log_cursor.node)
          @undo_log = undo_log
          @undo_record_cursor = @undo_log.undo_record_cursor(:min, @direction)
        end

        @undo_record_cursor.undo_record
      end

      def prev_undo_record
        if (rec = @undo_log_cursor.undo_record)
          return rec
        end

        if (undo_log = @undo_log_cursor.node)
          @undo_log = undo_log
          @undo_record_cursor = @undo_log.undo_record_cursor(:max, @direction)
        end

        @undo_record_cursor.undo_record
      end

      def each_undo_record
        return enum_for(:each_undo_record) unless block_given?

        while (rec = undo_record)
          yield rec
        end
      end
    end

    def undo_record_cursor(undo_record = :min, direction = :forward)
      UndoRecordCursor.new(self, undo_record, direction)
    end

    def each_undo_record(&block)
      return enum_for(:each_undo_record) unless block_given?

      undo_record_cursor.each_undo_record(&block)
    end
  end
end