class Zip::ExtraField::Zip64

def ==(other)
  other.original_size == @original_size &&
    other.compressed_size == @compressed_size &&
    other.relative_header_offset == @relative_header_offset &&
    other.disk_start_number == @disk_start_number
end

def extract(size, format)
  @content.slice!(0, size).unpack1(format)
end

def initialize(binstr = nil)
  # unparsed binary; we don't actually know what this contains
  # without looking for FFs in the associated file header
  # call parse after initializing with a binary string
  @content                = nil
  @original_size          = nil
  @compressed_size        = nil
  @relative_header_offset = nil
  @disk_start_number      = nil
  binstr && merge(binstr)
end

def merge(binstr)
  return if binstr.empty?
  _, @content = initial_parse(binstr)
end

def pack_for_c_dir
  # central directory entries contain only fields that didn't fit in the main entry part
  packed = ''.force_encoding('BINARY')
  packed << [@original_size].pack('Q<') if @original_size
  packed << [@compressed_size].pack('Q<') if @compressed_size
  packed << [@relative_header_offset].pack('Q<') if @relative_header_offset
  packed << [@disk_start_number].pack('V') if @disk_start_number
  packed
end

def pack_for_local
  # local header entries must contain original size and compressed size; other fields do not apply
  return '' unless @original_size && @compressed_size
  [@original_size, @compressed_size].pack('Q<Q<')
end

def parse(original_size, compressed_size, relative_header_offset = nil, disk_start_number = nil)
  @original_size = extract(8, 'Q<') if original_size == 0xFFFFFFFF
  @compressed_size = extract(8, 'Q<') if compressed_size == 0xFFFFFFFF
  @relative_header_offset = extract(8, 'Q<') if relative_header_offset && relative_header_offset == 0xFFFFFFFF
  @disk_start_number = extract(4, 'V') if disk_start_number && disk_start_number == 0xFFFF
  @content = nil
  [@original_size || original_size,
   @compressed_size || compressed_size,
   @relative_header_offset || relative_header_offset,
   @disk_start_number || disk_start_number]
end