Does **most** of the work when migrating from JSON.mapping to JSON::Serializable

json_mapping_replacer.rb

file_data = File.read(ARGV[0])

mapping_regex = /^[ ]+?JSON\.mapping\(\{?$\n(^.+?,?$\n)+?\s+\}?\)/m

file_data.gsub!(mapping_regex) do |match|
  result = ''
  lines = match.split("\n")
  lines.each.with_index do |line, i|
    if i.zero?
      result << line.sub(/JSON\.mapping\(\{?/, 'include JSON::Serializable') + "\n\n"
    elsif i == lines.size - 1
      # Do not paste line
    else
      line.rstrip!
      line.delete_prefix!('  ') # Remove intendation
      line.delete_suffix!(',')
      line.sub!(/^(\s+)(\w+):\s+(.+)/) do
        intendation = $1
        name = $2
        data = $3

        if data.start_with?('{')
          field_data = data.dup
          field_data.delete_prefix!('{')
          field_data.delete_suffix!('}')

          type = nil
          field_data.sub!(/(?:, )?type: ([^,]+)(?:, )?/) do |match|
            type = $1
            if match.start_with?(', ') && match.end_with?(', ')
              ', '
            else
              ''
            end
          end

          data_line = field_data.empty? ? '' : "#{intendation}@[JSON::Field(#{field_data})]\n"
          property_line = "#{intendation}property #{name} : #{type}"

          data_line + property_line
        else
          "#{intendation}property #{name} : #{data}"
        end
      end
      result << line + (i == lines.size - 2 ? "" : "\n")
    end
  end

  result
end

File.write(ARGV[0], file_data)