# frozen_string_literal: true

require "innodb/list"
require "innodb/xdes"

# A specialized class for FSP_HDR (filespace header) and XDES (extent
# descriptor) page types. Each tablespace always has an FSP_HDR page as
# its first page (page 0), and has repeating XDES pages every 16,384 pages
# after that (page 16384, 32768, ...). The FSP_HDR and XDES page structure
# is completely identical, with the exception that the FSP header structure
# is zero-filled on XDES pages, but populated on FSP_HDR pages.
#
# The basic structure of FSP_HDR and XDES pages is: FIL header, FSP header,
# an array of 256 XDES entries, empty (unused) space, and FIL trailer.
module Innodb
  class Page
    class FspHdrXdes < Page
      extend ReadBitsAtOffset

      specialization_for :FSP_HDR
      specialization_for :XDES

      Flags = Struct.new(
        :system_page_size,
        :compressed,
        :page_size,
        :post_antelope,
        :atomic_blobs,
        :data_directory,
        :value,
        keyword_init: true
      )

      Header = Struct.new(
        :space_id,
        :unused,
        :size, # rubocop:disable Lint/StructNewOverride
        :free_limit,
        :flags,
        :frag_n_used,
        :free,
        :free_frag,
        :full_frag,
        :first_unused_seg,
        :full_inodes,
        :free_inodes,
        keyword_init: true
      )

      EncryptionHeader = Struct.new(
        :magic,
        :master_key_id,
        :key,
        :iv,
        :server_uuid,
        :checksum,
        keyword_init: true
      )

      SdiHeader = Struct.new(
        :version,
        :root_page_number,
        keyword_init: true
      )

      # A value added to the adjusted exponent stored in the page size field of
      # the flags in the FSP header.
      FLAGS_PAGE_SIZE_SHIFT = 9

      def self.shift_page_size(page_size_shifted)
        (1 << (FLAGS_PAGE_SIZE_SHIFT + page_size_shifted)) if page_size_shifted != 0
      end

      # Decode the "flags" field in the FSP header, returning a hash of useful
      # decodings of the flags (based on MySQl 5.6 definitions). The flags are:
      #
      # Offset    Size    Description
      # 0         1       Post-Antelope Flag.
      # 1         4       Compressed Page Size (zip_size). This is stored as a
      #                   power of 2, minus 9. Since 0 is reserved to mean "not
      #                   compressed", the minimum value is 1, thus making the
      #                   smallest page size 1024 (2 ** (9 + 1)).
      # 5         1       Atomic Blobs Flag.
      # 6         4       System Page Size (innodb_page_size, UNIV_PAGE_SIZE).
      #                   The setting of the system page size when the tablespace
      #                   was created, stored in the same format as the compressed
      #                   page size above.
      # 10        1       Data Directory Flag.
      #
      def self.decode_flags(flags)
        system_page_size =
          shift_page_size(read_bits_at_offset(flags, 4, 6)) ||
          Innodb::Space::DEFAULT_PAGE_SIZE
        compressed_page_size = shift_page_size(read_bits_at_offset(flags, 4, 1))

        Flags.new(
          system_page_size: system_page_size,
          compressed: compressed_page_size ? false : true,
          page_size: compressed_page_size || system_page_size,
          post_antelope: read_bits_at_offset(flags, 1, 0) == 1,
          atomic_blobs: read_bits_at_offset(flags, 1, 5) == 1,
          data_directory: read_bits_at_offset(flags, 1, 10) == 1,
          value: flags
        )
      end

      # The FSP header immediately follows the FIL header.
      def pos_fsp_header
        pos_page_body
      end

      # The FSP header contains six 32-bit integers, one 64-bit integer, and 5
      # list base nodes.
      def size_fsp_header
        ((4 * 6) + (1 * 8) + (5 * Innodb::List::BASE_NODE_SIZE))
      end

      # The XDES entry array immediately follows the FSP header.
      def pos_xdes_array
        pos_fsp_header + size_fsp_header
      end

      # The number of entries in the XDES array. Defined as page size divided by
      # extent size.
      def entries_in_xdes_array
        size / space.pages_per_extent
      end

      def size_xdes_entry
        @size_xdes_entry ||= Innodb::Xdes.new(self, cursor(pos_xdes_array)).size_entry
      end

      def size_xdes_array
        entries_in_xdes_array * size_xdes_entry
      end

      def pos_encryption_header
        pos_xdes_array + size_xdes_array
      end

      def size_encryption_header
        3 + 4 + (32 * 2) + 36 + 4 + 4
      end

      def pos_sdi_header
        pos_encryption_header + size_encryption_header
      end

      def size_sdi_header
        8
      end

      # Read the FSP (filespace) header, which contains a few counters and flags,
      # as well as list base nodes for each list maintained in the filespace.
      def fsp_header
        @fsp_header ||= cursor(pos_fsp_header).name("fsp") do |c|
          Header.new(
            space_id: c.name("space_id") { c.read_uint32 },
            unused: c.name("unused") { c.read_uint32 },
            size: c.name("size") { c.read_uint32 },
            free_limit: c.name("free_limit") { c.read_uint32 },
            flags: c.name("flags") { self.class.decode_flags(c.read_uint32) },
            frag_n_used: c.name("frag_n_used") { c.read_uint32 },
            free: c.name("list[free]") { Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c)) },
            free_frag: c.name("list[free_frag]") { Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c)) },
            full_frag: c.name("list[full_frag]") { Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c)) },
            first_unused_seg: c.name("first_unused_seg") { c.read_uint64 },
            full_inodes: c.name("list[full_inodes]") { Innodb::List::Inode.new(@space, Innodb::List.get_base_node(c)) },
            free_inodes: c.name("list[free_inodes]") { Innodb::List::Inode.new(@space, Innodb::List.get_base_node(c)) }
          )
        end
      end

      # Iterate through all lists in the file space.
      def each_list
        return enum_for(:each_list) unless block_given?

        fsp_header.to_h.each do |key, value|
          yield key, value if value.is_a?(Innodb::List)
        end
      end

      # Iterate through all XDES entries in order. This is useful for debugging,
      # but each of these entries is actually a node in some other list. The state
      # field in the XDES entry indicates which type of list it is present in,
      # although not necessarily which list (e.g. :fseg).
      def each_xdes
        return enum_for(:each_xdes) unless block_given?

        cursor(pos_xdes_array).name("xdes_array") do |c|
          entries_in_xdes_array.times do
            yield Innodb::Xdes.new(self, c)
          end
        end
      end

      def encryption_header
        @encryption_header ||= cursor(pos_encryption_header).name("encryption_header") do |c|
          EncryptionHeader.new(
            magic: c.name("magic") { c.read_bytes(3) },
            master_key_id: c.name("master_key_id") { c.read_uint32 },
            key: c.name("key") { c.read_bytes(32) },
            iv: c.name("iv") { c.read_bytes(32) },
            server_uuid: c.name("server_uuid") { c.read_string(36) },
            checksum: c.name("checksum") { c.read_uint32 }
          )
        end
      end

      def sdi_header
        @sdi_header ||= cursor(pos_sdi_header).name("sdi_header") do |c|
          SdiHeader.new(
            version: c.name("version") { c.read_uint32 },
            root_page_number: c.name("root_page_number") { c.read_uint32 }
          )
        end
      end

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

        super

        yield Region.new(
          offset: pos_fsp_header,
          length: size_fsp_header,
          name: :fsp_header,
          info: "FSP Header"
        )

        each_xdes do |xdes|
          state = xdes.state || "unused"
          yield Region.new(
            offset: xdes.offset,
            length: size_xdes_entry,
            name: :"xdes_#{state}",
            info: "Extent Descriptor (#{state})"
          )
        end

        yield Region.new(
          offset: pos_encryption_header,
          length: size_encryption_header,
          name: :encryption_header,
          info: "Encryption Header"
        )

        yield Region.new(
          offset: pos_sdi_header,
          length: size_sdi_header,
          name: :sdi_header,
          info: "SDI Header"
        )

        nil
      end

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

        puts "fsp header:"
        pp fsp_header
        puts

        puts "xdes entries:"
        each_xdes do |xdes|
          pp xdes
        end
        puts

        puts "encryption header:"
        pp encryption_header
        puts

        puts "serialized dictionary information header:"
        pp sdi_header
        puts
      end
    end
  end
end