A Ruby parser which parses EastAsianWidth.txt from UAX #11 at https://www.unicode.org/reports/tr11/

east_asian_width.rb

# frozen_string_literal: true

# Copyright (c) 2022 Weihang Jian <https://tonytonyjan.net>
#
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# SOFTWARE.

# A parser which parses EastAsianWidth-14.0.0.txt
# For more information, see UAX #11: East Asian Width,
# at https://www.unicode.org/reports/tr11/
#
# == Example
#
#   eaw = EastAsianWidth.new(File.read('EastAsianWidth.txt'))
#   puts %w[test 測試! 測試！].map{ eaw.string_width(_1) }
#
# Output:
#
#   4
#   5
#   6
#
class EastAsianWidth
  def initialize(east_asian_width_txt_data)
    @lookup_table = []
    east_asian_width_txt_data.each_line do |line|
      next unless line.start_with?(/[0-9A-F]/)

      code_point, property = line[0, 16].split(';')
      property.rstrip!
      if code_point.include?('..')
        first, last = code_point.split('..')
        @lookup_table << [first.to_i(16)..last.to_i(16), property]
      else
        @lookup_table << [code_point.to_i(16), property]
      end
    end
  end

  def string_width(string)
    string.codepoints.sum { lookup_width(_1) }
  end

  def lookup_width(code_point)
    property = lookup(code_point)
    case property
    when 'Na', 'H' then 1
    when 'W', 'F' then 2
    else
      warn "code point 0x#{code_point.to_s(16)} has property #{property}"
      1
    end
  end

  def lookup(code_point)
    @lookup_table.find do |integer_of_range, property|
      return property if integer_of_range.is_a?(Range) && integer_of_range.cover?(code_point)
      return property if integer_of_range.is_a?(Integer) && integer_of_range == code_point
    end
    raise "missing code point 0x#{code_point.to_s(16)}"
  end
end