class TTFunk::Table::Cff::Encoding

def [](glyph_id)
  return 0 if glyph_id.zero?
  return code_for(glyph_id) if offset
  self.class.codes_for_encoding_id(offset_or_id)[glyph_id]
end

def code_for(glyph_id)
  return 0 if glyph_id.zero?
  # rather than validating the glyph as part of one of the predefined
  # encodings, just pass it through
  return glyph_id unless offset
  case format_sym
  when :array_format, :supplemental
    @entries[glyph_id]
  when :range_format
    remaining = glyph_id
    @entries.each do |range|
      if range.size >= remaining
        return (range.first + remaining) - 1
      end
      remaining -= range.size
    end
    0
  end
end

def codes_for_encoding_id(encoding_id)
  case encoding_id
  when STANDARD_ENCODING_ID
    Encodings::STANDARD
  when EXPERT_ENCODING_ID
    Encodings::EXPERT
  end
end

def each
  return to_enum(__method__) unless block_given?
  # +1 adjusts for the implicit .notdef glyph
  (items_count + 1).times { |i| yield(self[i]) }
end

def element_format(fmt = format_sym)
  {
    array_format: 'C',
    range_format: 'CC',
    supplemental: 'Cn',
  }[fmt]
end

def element_width(fmt = format_sym)
  case fmt
  when :array_format then 1
  when :range_format then 2
  when :supplemental then 3
  else
    raise Error, "'#{fmt}' is an unsupported encoding format"
  end
end

def encode(charmap)
  # Any subset encoding is all but guaranteed to be different from the
  # standard encoding so we don't even attempt to see if it matches. We
  # assume it's different and just encode it anew.
  return encode_supplemental(charmap) if supplemental?
  codes =
    charmap
      .reject { |_code, mapping| mapping[:new].zero? }
      .sort_by { |_code, mapping| mapping[:new] }
      .map { |(code, _m)| code }
  ranges = TTFunk::BinUtils.rangify(codes)
  # calculate whether storing the charset as a series of ranges is
  # more efficient (i.e. takes up less space) vs storing it as an
  # array of SID values
  total_range_size = (2 * ranges.size) +
    (element_width(:range_format) * ranges.size)
  total_array_size = codes.size * element_width(:array_format)
  if total_array_size <= total_range_size
    ([format_int(:array_format), codes.size] + codes).pack('C*')
  else
    element_fmt = element_format(:range_format)
    result = [format_int(:range_format), ranges.size].pack('CC')
    ranges.each { |range| result << range.pack(element_fmt) }
    result
  end
end

def encode_supplemental(charmap)
  new_entries =
    charmap
      .reject { |_code, mapping| mapping[:new].zero? }
      .transform_values { |mapping| mapping[:new] }
  result = [format_int(:supplemental), new_entries.size].pack('CC')
  fmt = element_format(:supplemental)
  new_entries.each do |code, new_gid|
    result << [code, new_gid].pack(fmt)
  end
  result
end

def format_int(sym = format_sym)
  case sym
  when :array_format then 0
  when :range_format then 1
  when :supplemental then 129
  else
    raise Error, "unsupported charset format '#{sym}'"
  end
end

def format_sym
  return :supplemental if supplemental?
  case @format
  when 0 then :array_format
  when 1 then :range_format
  else
    raise Error, "unsupported charset format '#{fmt}'"
  end
end

def initialize(top_dict, file, offset_or_id = nil, length = nil)
  @top_dict = top_dict
  @offset_or_id = offset_or_id || DEFAULT_ENCODING_ID
  if offset
    super(file, offset, length)
    @supplemental = format >> 7 == 1
  else
    @items_count = self.class.codes_for_encoding_id(offset_or_id).size
    @supplemental = false
  end
end

def offset
  # Numbers from 0..1 mean encoding IDs instead of offsets. IDs are
  # pre-defined, generic encodings that define the characters present
  # in the font.
  #
  # In the case of an offset, add the CFF table's offset since the
  # charset offset is relative to the start of the CFF table. Otherwise
  # return nil (no offset).
  if offset_or_id > 1
    offset_or_id + top_dict.cff_offset
  end
end

def parse!
  @format, entry_count = read(2, 'C*')
  @length = entry_count * element_width
  case format_sym
  when :array_format
    @items_count = entry_count
    @entries = OneBasedArray.new(read(length, 'C*'))
  when :range_format
    @entries = []
    @items_count = 0
    entry_count.times do
      code, num_left = read(element_width, element_format)
      @entries << (code..(code + num_left))
      @items_count += num_left + 1
    end
  when :supplemental
    @entries = {}
    @items_count = entry_count
    entry_count.times do
      code, glyph = read(element_width, element_format)
      @entries[code] = glyph
    end
  end
end

def supplemental?
  # high-order bit set to 1 indicates supplemental encoding
  @supplemental
end