require 'binary_struct'
require 'manageiq/gems/pending'
require 'util/miq-hash_struct'

module MiqBerkeleyDB
  class MiqBdbPage
    # Page numbers.
    PGNO_INVALID = 0
    PGNO_BASE_MD = 0

    # Page types
    P_INVALID       = 0   # Invalid page type
    P_DUPLICATE     = 1   # Duplicate. DEPRECATED in 3.1
    P_HASH          = 2   # Hash
    P_IBTREE        = 3   # Btree internal
    P_IRECNO        = 4   # Recno internal
    P_LBTREE        = 5   # Btree leaf
    P_LRECNO        = 6   # Recno leaf
    P_OVERFLOW      = 7   # Overflow
    P_HASHMETA      = 8   # Hash metadata page
    P_BTREEMETA     = 9   # Btree metadata page
    P_QAMMETA       = 10  # Queue metadata page
    P_QAMDATA       = 11  # Queue data page
    P_LDUP          = 12  # Off-page duplicate leaf

    def self.type2string(t)
      case t
      when P_INVALID then   "invalid"
      when P_DUPLICATE then "duplicate (deprecated)"
      when P_HASH then      "hash"
      when P_IBTREE then    "btree internal"
      when P_IRECNO then    "recno internal"
      when P_LBTREE then    "btree leaf"
      when P_LRECNO then    "recno leaf"
      when P_OVERFLOW then  "overflow"
      when P_HASHMETA then  "hash metadata"
      when P_BTREEMETA then "btree metadata"
      when P_QAMMETA then   "queue metadata"
      when P_QAMDATA then   "queue data"
      when P_LDUP then      "offpage duplicate leaf"
      else                  "unknown value of #{t}"
      end
    end

    # Page Header.
    HEADER = BinaryStruct.new([
      # 00-07: Log sequence number (LSN)
      'L', 'lsn_file',        #   0-3: LSN File
      'L', 'lsn_offset',      #   4-7: LSN Offset
      'L', 'pgno',            # 08-11: Current page number
      'L', 'prev_pgno',       # 12-15: Previous page number
      'L', 'next_pgno',       # 16-19: Next page number
      'S', 'entries',         # 20-21: Number of items on the page
      'S', 'hf_offset',       # 22-23: High free byte page offset
      'C', 'level',           #    24: Btree tree level
      'C', 'p_type'           #    25: Page type
    ])

    SIZEOF_HEADER = HEADER.size

    #
    # With many compilers sizeof(PAGE) == 28, while SIZEOF_PAGE == 26.
    # We add in other things directly after the page header and need
    # the SIZEOF_PAGE.  When giving the sizeof(), many compilers will
    # pad it out to the next 4-byte boundary.
    #
    SIZEOF_PAGE = 26

    attr_reader :header, :data, :pagesize, :buf

    def self.getPage(db, pagenum)
      return nil if pagenum == PGNO_INVALID
      #     return nil if pagenum >= db.npages

      buf = db.bdb.readPage(pagenum)
      return nil if buf.nil? || buf[25, 1].ord == P_INVALID
      MiqBdbPage.new(buf, db)
    end

    def initialize(buf, db)
      raise "Nil buffer." if buf.nil?
      @db         = db
      @buf        = buf
      @pagesize   = buf.size
      @header     = HEADER.decode(@buf[0, SIZEOF_HEADER])
      @data       = buf[SIZEOF_HEADER..-1]
    end

    def current
      @header['pgno']
    end

    def next
      @header['next_pgno']
    end

    def prev
      @header['prev_pgno']
    end

    def nentries
      @header['entries']
    end

    def offset
      @header['hf_offset']
    end

    def level
      @header['level']
    end

    def ptype
      @header['p_type']
    end

    def keys
      @db.keys(self) { |k| yield k }
    end

    def values
      @db.values(self) { |v| yield v }
    end

    def pairs
      @db.pairs(self) { |k, v| yield k, v }
    end

    # Dump page statistics like db_dump.
    def dump
      out  = ""
      out << "Page #{current}\n"
      out << "  type:            #{MiqBdbPage.type2string(ptype)}\n"
      out << "  prev:            #{prev}\n"
      out << "  next:            #{@header['next_pgno']}\n"
      out << "  log seq num:     file=#{@header['lsn_file']}  offset=#{@header['lsn_offset']}\n"
      out << "  level:           #{level}\n"

      if @header['p_type'] == P_OVERFLOW
        out << "  ref cnt:         #{nentries}\n"
        out << "  len:             #{offset}\n"
      else
        out << "  entries:         #{nentries}\n"
        out << "  offset:          #{offset}\n"
      end
      out << "  data size:       #{@data.size}\n"
      out << "  data:            "

      @data.bytes.take(20).each do |c|
        out << sprintf("%.2x ", c)
      end
      out << "..." if @data.size > 20

      out << "\n\n"
      out
    end
  end
end