Extract each font file from TTC font collection file

extract_ttf_from_ttc.rb

# See <https://docs.microsoft.com/en-us/typography/opentype/spec/otff#font-collections>

ttc = ARGF

unless ttc.read(4) == "ttcf"
  STDERR.puts "Not TTC file."
  exit 1
end

major_version, minor_version = ttc.read(4).unpack("nn")
puts "Version: #{major_version}.#{minor_version}"

num_fonts = ttc.read(4).unpack("N").first
puts "Number of fonts: #{num_fonts}"

offsets = num_fonts.times.map do
  ttc.read(4).unpack("N").first
end

num_fonts.times do |i|
  offset = offsets[i]
  puts "Extract font at offset: #{offset}"

  ttc.seek(offset)

  content = if i + 1 < num_fonts
    size = offsets[i + 1] - offset
    ttc.read(size)
  else
    # Read towards the end of file.
    ttc.read
  end

  File.write("#{i}.ttf", content)
end