i18n positions

ruby.rb

# heavily based on Masao Mutoh's gettext String interpolation extension
# http://github.com/mutoh/gettext/blob/f6566738b981fe0952548c421042ad1e0cdfb31e/lib/gettext/core_ext/string.rb

module I18n
  INTERPOLATION_PATTERN = Regexp.union(
    /%%/,
    /%\{(\w+)\}/,                               # matches placeholders like "%{foo}"
    /%<(\w+)>(.*?\d*\.?\d*[bBdiouxXeEfgGcps])/  # matches placeholders like "%<foo>.d"
  )

  class << self
    def interpolate(string, values)
      raise ReservedInterpolationKey.new($1.to_sym, string) if string =~ RESERVED_KEYS_PATTERN
      raise ArgumentError.new('Interpolation values must be a Hash.') unless values.kind_of?(Hash)
      interpolate_hash(string, values)
    end

    def interpolate_hash(string, values)
      # def string.position_foo
      #   @positions ||= {}
      # end
      positions = {}
      offset = 0
      string.gsub(INTERPOLATION_PATTERN) do |match|
        if match == '%%'
          '%'
        else
          key = ($1 || $2).to_sym
          value = values.key?(key) ? values[key] : raise(MissingInterpolationArgument.new(values, string))
          value = value.call(values) if value.respond_to?(:call)

          # puts "value: #{value} (start: #{$~.begin(1)}, end:#{$~.begin(1) + value.length})"

          positions[key] = [offset + $~.begin(1) - 2, offset + $~.begin(1) - 2 + value.length - 1]
          # %{name}   %{position}
          # David     Toronto

          offset + value.length - (key.size + 3)
          $3 ? sprintf("%#{$3}", value) : value
        end
      end.tap{|result|
        result.translation_metadata[:positions] = positions if result.respond_to?(:translation_metadata)
      }
    end
  end
end