class Unicode::DisplayWidth

def self.decompress_index(index, level)
  index.flat_map{ |value|
    if level > 0
      if value.instance_of?(Array)
        value[15] ||= nil
        decompress_index(value, level - 1)
      else
        decompress_index([value] * 16, level - 1)
      end
    else
      if value.instance_of?(Array)
        value[15] ||= nil
        value
      else
        [value] * 16
      end
    end
  }
end

def self.emoji_width(string, mode = :all, ambiguous = DEFAULT_AMBIGUOUS)
  res = 0
  if emoji_set_regex = EMOJI_SEQUENCES_REGEX_MAPPING[mode]
    emoji_width_via_possible(
      string,
      Unicode::Emoji.const_get(emoji_set_regex),
      mode == :rgi_at,
      ambiguous,
    )
  elsif mode == :all_no_vs16
    no_emoji_string = string.gsub(REGEX_EMOJI_ALL_SEQUENCES){ res += 2; "" }
    [res, no_emoji_string]
  elsif mode == :vs16
    no_emoji_string = string.gsub(REGEX_EMOJI_VS16){ res += 2; "" }
    [res, no_emoji_string]
  elsif mode == :all
    no_emoji_string = string.gsub(REGEX_EMOJI_ALL_SEQUENCES_AND_VS16){ res += 2; "" }
    [res, no_emoji_string]
  else
    [0, string]
  end
end

def self.emoji_width_via_possible(string, emoji_set_regex, strict_eaw = false, ambiguous = DEFAULT_AMBIGUOUS)
  res = 0
  # For each string possibly an emoji
  no_emoji_string = string.gsub(REGEX_EMOJI_ALL_SEQUENCES_AND_VS16){ |emoji_candidate|
    # Check if we have a combined Emoji with width 2 (or EAW an Apple Terminal)
    if emoji_candidate == emoji_candidate[emoji_set_regex]
      if strict_eaw
        res += self.of(emoji_candidate[0], ambiguous, emoji: false)
      else
        res += 2
      end
      ""
    # We are dealing with a default text presentation emoji or a well-formed sequence not matching the above Emoji set
    else
      if !strict_eaw
        # Ensure all explicit VS16 sequences have width 2
        emoji_candidate.gsub!(REGEX_EMOJI_VS16){ res += 2; "" }
      end
      emoji_candidate
    end
  }
  [res, no_emoji_string]
end

def self.normalize_options(string, ambiguous = nil, overwrite = nil, old_options = {}, **options)
  unless old_options.empty?
    warn "Unicode::DisplayWidth: Please migrate to keyword arguments - #{old_options.inspect}"
    options.merge! old_options
  end
  options[:ambiguous] = ambiguous if ambiguous
  options[:ambiguous] ||= DEFAULT_AMBIGUOUS
  if options[:ambiguous] != 1 && options[:ambiguous] != 2
    raise ArgumentError, "Unicode::DisplayWidth: Ambiguous width must be 1 or 2"
  end
  if overwrite && !overwrite.empty?
    warn "Unicode::DisplayWidth: Please migrate to keyword arguments - overwrite: #{overwrite.inspect}"
    options[:overwrite] = overwrite
  end
  options[:overwrite] ||= {}
  if [nil, true, :auto].include?(options[:emoji])
    options[:emoji] = EmojiSupport.recommended
  elsif options[:emoji] == false
    options[:emoji] = :none
  end
  options
end

def self.of(string, ambiguous = nil, overwrite = nil, old_options = {}, **options)
  # Binary strings don't make much sense when calculating display width.
  # Assume it's valid UTF-8
  if string.encoding == Encoding::BINARY && !string.force_encoding(Encoding::UTF_8).valid_encoding?
    # Didn't work out, go back to binary
    string.force_encoding(Encoding::BINARY)
  end
  string = string.encode(Encoding::UTF_8, invalid: :replace, undef: :replace) unless string.encoding == Encoding::UTF_8
  options = normalize_options(string, ambiguous, overwrite, old_options, **options)
  width = 0
  unless options[:overwrite].empty?
    width, string = width_custom(string, options[:overwrite])
  end
  if string.ascii_only?
    return width + width_ascii(string)
  end
  ambiguous_index_name = AMBIGUOUS_MAP[options[:ambiguous]]
  unless string.match?(NOT_COMMON_NARROW_REGEX[ambiguous_index_name])
    return width + string.size
  end
  # Retrieve Emoji width
  if options[:emoji] != :none
    e_width, string = emoji_width(
      string,
      options[:emoji],
      options[:ambiguous],
    )
    width += e_width
    unless string.match?(NOT_COMMON_NARROW_REGEX[ambiguous_index_name])
      return width + string.size
    end
  end
  index_full = INDEX[ambiguous_index_name]
  index_low = FIRST_4096[ambiguous_index_name]
  first_ambiguous = FIRST_AMBIGUOUS[ambiguous_index_name]
  string.each_codepoint{ |codepoint|
    if codepoint > 15 && codepoint < first_ambiguous
      width += 1
    elsif codepoint < 0x1001
      width += index_low[codepoint] || 1
    else
      d = INITIAL_DEPTH
      w = index_full[codepoint / d]
      while w.instance_of? Array
        w = w[(codepoint %= d) / (d /= 16)]
      end
      width += w || 1
    end
  }
  # Return result + prevent negative lengths
  width < 0 ? 0 : width
end

def self.width_ascii(string)
  if string.match?(ASCII_NON_ZERO_REGEX)
    res = string.delete(ASCII_NON_ZERO_STRING).bytesize - string.count(ASCII_BACKSPACE)
    return res < 0 ? 0 : res
  end
  string.bytesize
end

def self.width_custom(string, overwrite)
  width = 0
  string = string.each_codepoint.select{ |codepoint|
    if overwrite[codepoint]
      width += overwrite[codepoint]
      nil
    else
      codepoint
    end
  }.pack("U*")
  [width, string]
end

def get_config(**kwargs)
  {
    ambiguous: kwargs[:ambiguous] || @ambiguous,
    overwrite: kwargs[:overwrite] || @overwrite,
    emoji:     kwargs[:emoji]     || @emoji,
  }
end

def initialize(ambiguous: DEFAULT_AMBIGUOUS, overwrite: {}, emoji: true)
  @ambiguous = ambiguous
  @overwrite = overwrite
  @emoji     = emoji
end

def of(string, **kwargs)
  self.class.of(string, **get_config(**kwargs))
end