Track sleep of the computer with Mac OSX agent config for autoload

ilya.track_sleep.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
        <dict>
                <key>Label</key>
                <string>ilya.track_sleep</string>
                <key>Program</key>
                <string>/Users/sa/track_sleep.rb</string>
                <key>WorkingDirectory</key>
                <string>/Users/sa</string>
                <key>RunAtLoad</key>
                <true/>
                <key>KeepAlive</key>
                <true/>
        </dict>
</plist>

load-or-unload

# run this to load the agent
launchctl load ~/Library/LaunchAgents/ilya.track_sleep.plist

# run this to unload the agent and stop the process
launchctl unload ~/Library/LaunchAgents/ilya.track_sleep.plist

# to apply config change, must unload and load

track_sleep.rb

#!/usr/bin/env ruby
def log(str)
  # will always create log file in current working directory
  open('track_sleep.log','a'){|f| f.puts str }
end

now=Time.now
log "*** #{now.strftime("%Y-%m-%d %a %H:%M:%S")}: Started"
while true
  now, past = Time.now, now
  diff = (now-past).to_i
  if diff>15*60
    prev, last = last, now
    log "Work: #{prev.strftime("%Y-%m-%d %a %H:%M")} -> #{past.strftime("%H:%M")}" if prev && past>prev && past.day==prev.day
    
    # this part might be important in case of progam restart, when it won't have previous time
    log "Sleep: #{past.strftime("%Y-%m-%d %a %H:%M:%S")} -> #{now.strftime("%Y-%m-%d %a %H:%M:%S")} (#{diff/3600}:#{(diff%3600)/60}:#{diff%60})"
  end
  sleep 10
end