#!/usr/bin/env python

import sys
import subprocess

DEFAULT_TEMPERATURE = 3500

try:
    with open('/tmp/temperature', 'r') as temp_file:
        current_temperature = int(temp_file.read())
except FileNotFoundError:
    current_temperature = DEFAULT_TEMPERATURE

# If no argument is given print the current temperature
if len(sys.argv) == 1:
    print(current_temperature)
    sys.exit(0)
elif len(sys.argv) != 2:
    print("""
Usage:

  screen-temperature
      print current temperature

  screen-temperature <temperature>
      set screen temperature to <temperature>

  screen-temperature <+|-><temperature>
      increase or decrease screen temperature by <temperature>
""")
    sys.exit(1)

temperature_change = sys.argv[1]

if temperature_change.startswith("+"):
    new_temperature = current_temperature + int(temperature_change[1:])
elif temperature_change.startswith("-"):
    new_temperature = current_temperature - int(temperature_change[1:])
else:
    new_temperature = int(temperature_change)

try:
    subprocess.run(["redshift", "-O", str(new_temperature), "-P"], check=True)
    with open('/tmp/temperature', 'w') as temp_file:
        temp_file.write(str(new_temperature) + '\n')
except subprocess.CalledProcessError:
    print("Error: could not set screen temperature.")
    sys.exit(1)