You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: app.rb
    path of file: ./repos/mytime.io
    
    the code of the file until where you have to start completion: require 'sinatra'
require '
    
def parse_timezone(string)
  tz = string.upcase
  supported_timezones = ["GMT", "UTC", "UT", "PST", "PDT",  "CST", "CDT", "MST", "MDT"]
  if supported_timezones.include? tz
    @time_zone = tz
    return tz 
  else
    guessed_offset = TimezoneParser::Abbreviation.new(tz).getOffsets.first
    if guessed_offset.nil?
      if tz.start_with? "UTC" or tz.start_with? "GMT"
        offset_regex = /^([+]((14|(14[:]?00))|([0][0-9]|[1][01])|([0][0-9]|[1][01])[:]?[0-5][0-9]))|([-]((12|(12[:]?00))|([0][0-9]|[1][01])|([0][0-9]|[1][01])[:]?[0-5][0-9]))$/
        if  offset_regex.match(tz.sub(/^(UTC|GMT)/, '')).nil?
          return nil
        else
          @time_zone = tz
          return tz
        end