Monitor iOS battery level and stop charging when the level >= 80% (restart when the level < 80%)

monitor_ios_battery.rb

#!/usr/bin/ruby
require 'timeout'

THRESH = 80 # %
SPEED = 60  # sec / %
$IDEVICEINFO_CMD = '/usr/local/bin/ideviceinfo'
$POWER_ON_CMD = 'curl -s -m 5 192.168.x.x/on'
$POWER_OFF_CMD = 'curl -s -m 5 192.168.x.x/off'
$state = nil
$caffe_pid = nil

trap(:CHLD, "IGNORE")

def get_batt(device_id)
  result = nil
  begin
    timeout(10) {
      result = `#{$IDEVICEINFO_CMD} -u #{device_id} -q com.apple.mobile.battery`
    }
  rescue => e
    STDERR.puts "#{Time.now}\t#{e}"
  end
  if result =~ /BatteryCurrentCapacity:\s*(\d+)/
    return $1.to_i
  end
  nil
end

def power_on
  if $state != :on
    puts "on:  " + `#{$POWER_ON_CMD}`
    $caffe_pid = fork { exec "caffeinate -i" }
    $state = :on
  end
end

def power_off
  if $state != :off
    puts "off: " + `#{$POWER_OFF_CMD}`
    $state = :off
    Process.kill :INT, $caffe_pid if $caffe_pid
    $caffe_pid = nil
  end
end


device_id = ARGV[0] || 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'  # default serial
reset_time = Time.now
last_time = Time.new(0)
last_batt = nil

loop do
  batt = get_batt device_id
  if batt

    last_time = Time.now
    last_batt = batt
    reset_time = last_time + [360, batt >= THRESH ? 360 : (THRESH - last_batt)*SPEED].min
    puts "#{last_time}\t#{batt}  # timeout: #{reset_time}"
    if batt < THRESH
      power_on
    else
      power_off
    end
    sleep 30

  else

    if Time.now - last_time <= 32
      sleep 30
      next
    end

    sleep 2

    if Time.now >= reset_time  # time out
      reset_time = Time.now + 120  # avoid frequent on/off
      # try turn on the device
      puts "#{Time.now}\t# reset"
      power_off
      sleep 10
      power_on

      now = Time.now
      if last_batt and last_batt + (now - last_time)/SPEED >= THRESH
        # turn off if estimated batt >= THRESH
        sleep 2
        power_off
      end
    end

  end
end