class TTFunk::Table::Kern

def self.encode(kerning, mapping)
  return unless kerning.exists? && kerning.tables.any?
  tables = kerning.tables.filter_map { |table| table.recode(mapping) }
  return if tables.empty?
  [0, tables.length, tables.join].pack('nnA*')
end

def add_table(format, attributes = {})
  if format.zero?
    @tables << Kern::Format0.new(attributes)
  end
  # Unsupported kerning tables are silently ignored
end

def parse!
  @version, num_tables = read(4, 'n*')
  @tables = []
  if @version == 1 # Mac OS X fonts
    @version = (@version << 16) + num_tables
    num_tables = read(4, 'N').first
    parse_version_1_tables(num_tables)
  else
    parse_version_0_tables(num_tables)
  end
end

def parse_version_0_tables(_num_tables)
  # It looks like some MS fonts report their kerning subtable lengths
  # wrong. In one case, the length was reported to be some 19366, and yet
  # the table also claimed to hold 14148 pairs (each pair consisting of
  # 6 bytes).  You do the math!
  #
  # We're going to assume that the microsoft fonts hold only a single
  # kerning subtable, which occupies the entire length of the kerning
  # table. Worst case, we lose any other subtables that the font contains,
  # but it's better than reading a truncated kerning table.
  #
  # And what's more, it appears to work. So.
  version, length, coverage = read(6, 'n*')
  format = coverage >> 8
  add_table(
    format,
    version: version,
    length: length,
    coverage: coverage,
    data: raw[10..],
    vertical: (coverage & 0x1).zero?,
    minimum: (coverage & 0x2 != 0),
    cross: (coverage & 0x4 != 0),
    override: (coverage & 0x8 != 0),
  )
end

def parse_version_1_tables(num_tables)
  num_tables.times do
    length, coverage, tuple_index = read(8, 'Nnn')
    format = coverage & 0x0FF
    add_table(
      format,
      length: length,
      coverage: coverage,
      tuple_index: tuple_index,
      data: io.read(length - 8),
      vertical: (coverage & 0x8000 != 0),
      cross: (coverage & 0x4000 != 0),
      variation: (coverage & 0x2000 != 0),
    )
  end
end