# frozen_string_literal: true

module Innodb
  class Page
    class UndoLog < Page
      specialization_for :UNDO_LOG

      PageHeader = Struct.new(
        :type,
        :latest_log_record_offset,
        :free_offset,
        :page_list_node,
        keyword_init: true
      )

      SegmentHeader = Struct.new(
        :state,
        :last_log_offset,
        :fseg,
        :page_list,
        keyword_init: true
      )

      def pos_undo_page_header
        pos_page_body
      end

      def size_undo_page_header
        2 + 2 + 2 + Innodb::List::NODE_SIZE
      end

      def pos_undo_segment_header
        pos_undo_page_header + size_undo_page_header
      end

      def size_undo_segment_header
        2 + 2 + Innodb::FsegEntry::SIZE + Innodb::List::BASE_NODE_SIZE
      end

      def pos_undo_logs
        pos_undo_segment_header + size_undo_segment_header
      end

      UNDO_PAGE_TYPES = {
        1 => :insert,
        2 => :update,
      }.freeze

      UNDO_SEGMENT_STATES = {
        1 => :active,
        2 => :cached,
        3 => :to_free,
        4 => :to_purge,
        5 => :prepared,
      }.freeze

      def undo_page_header
        @undo_page_header ||= cursor(pos_undo_page_header).name("undo_page_header") do |c|
          PageHeader.new(
            type: c.name("type") { UNDO_PAGE_TYPES[c.read_uint16] },
            latest_log_record_offset: c.name("latest_log_record_offset") { c.read_uint16 },
            free_offset: c.name("free_offset") { c.read_uint16 },
            page_list_node: c.name("page_list") { Innodb::List.get_node(c) }
          )
        end
      end

      def prev_address
        undo_page_header[:page_list_node][:prev]
      end

      def next_address
        undo_page_header[:page_list_node][:next]
      end

      def undo_segment_header
        @undo_segment_header ||= cursor(pos_undo_segment_header).name("undo_segment_header") do |c|
          SegmentHeader.new(
            state: c.name("state") { UNDO_SEGMENT_STATES[c.read_uint16] },
            last_log_offset: c.name("last_log_offset") { c.read_uint16 },
            fseg: c.name("fseg") { Innodb::FsegEntry.get_inode(@space, c) },
            page_list: c.name("page_list") { Innodb::List::UndoPage.new(@space, Innodb::List.get_base_node(c)) }
          )
        end
      end

      def undo_log(pos)
        Innodb::UndoLog.new(self, pos)
      end

      # Dump the contents of a page for debugging purposes.
      def dump
        super

        puts "undo page header:"
        pp undo_page_header
        puts

        puts "undo segment header:"
        pp undo_segment_header
        puts

        puts "last undo log:"
        undo_log(undo_segment_header[:last_log_offset]).dump unless undo_segment_header[:last_log_offset].zero?
        puts
      end
    end
  end
end