fix_gpx_times.rb

require 'rubygems'
require 'hpricot'
require 'time'

if ARGV.size < 1
    puts "Usage: fix_times.rb file.gpx"
    exit 2
end

File.open(ARGV[0]) do |f|
    gpx = Hpricot.XML(f)

    gpx.search('time').each do |time_elem|
        time = Time.parse(time_elem.innerText)
        new_time = time - (10 * 60 * 60) # 10 hours
        puts "#{time.iso8601} => #{new_time.iso8601}"
        time_elem.innerHTML = new_time.iso8601
    end
    
    # Write out modified version
    output_path = File.basename(f.path, File.extname(f.path)) + ' fixed' + File.extname(f.path)
    File.open(output_path, 'w') do |ofile|
        ofile.print gpx.to_s
    end
    puts "Fixed version written to #{output_path}"
end