get-daytime-period

#!/bin/sh
#
# Get/print the daytime period ("Night", "Day), possibly from redshift
# ("Night" / "Daytime" / "Transition").
#
# This uses DEFAULT_LATLON by default, because the geoclue provider is too
# fragile.  The result is cached for 10 minutes.

is_remote() {
  [ -n "$SSH_CONNECTION" ] && return
  # Container in OpenVZ?
  [ -r /proc/user_beancounters ] && ! [ -d /proc/bc ]
}
is_remote && USE_REDSHIFT=0 || USE_REDSHIFT=1

# Do not use geoclue by default, too slow and fragile.
# TODO: provide a method to easily update the latlonfile.
USE_GEOCLUE=0
GEOCLUE_TIMEOUT=2s
CACHE_SECONDS=600

if [ "$USE_REDSHIFT" = 1 ] && ! hash redshift 2> /dev/null; then
  echo "redshift not found." >&2
  USE_REDSHIFT=0
fi

cachefile=/tmp/redshift-period
ok_to_cache=1

get_period_by_hour() {
  hour=$(date +%H)
  if [ "$hour" -gt 8 ] && [ "$hour" -lt 20 ]; then
    printf "Daytime"
  else
    printf "Night"
  fi
}

# If not using `redshift`, just look at the current hour.
if [ "$USE_REDSHIFT" = 0 ]; then
  get_period_by_hour
  exit
fi

if [ -e "$cachefile" ]; then
  if [ "$(stat --format=%Y $cachefile)" -gt $(( $(date +%s) - CACHE_SECONDS )) ]; then
    cat $cachefile
    exit
  fi
fi

# Try geoclue.
if [ "$USE_GEOCLUE" = 1 ]; then
  geoclue_period=$(timeout $GEOCLUE_TIMEOUT redshift -l geoclue2 -p 2>/dev/null)
  timeout_ret=$?
  if [ "$timeout_ret" = 0 ]; then
    period=$(echo "$geoclue_period" | grep "^Period")
  else
    if [ "$timeout_ret" = 124 ]; then
      echo 'WARNING: redshift with geoclue timed out.' >&2
    else
      echo "WARNING: redshift failed with exit code $timeout_ret." >&2
    fi
    ok_to_cache=0
  fi
fi

if [ -z "$period" ]; then
  # Default lat/lon when geoclue is not used.
  DEFAULT_LATLON="$(dotfiles-decrypt U2FsdGVkX19+ff4P8pvhS2TzsJkKwrDGk/vD1IoXgdEbj3r9+4hfXsGpNfVqxkrR)"

  if [ -z "$DEFAULT_LATLON" ]; then
    echo "ERROR: $(basename "$0"): DEFAULT_LATLON is not defined." >&2
    exit 1
  fi
  period=$(redshift -l "$DEFAULT_LATLON" -p 2>/dev/null | grep "^Period")
fi

if [ -z "$period" ]; then
  echo "WARNING: failed to determine period using redshift." >&2
  echo "Falling back to get_period_by_hour." >&2
  get_period_by_hour
  exit
fi

period="${period#Period: }"
if [ "$ok_to_cache" = 1 ]; then
  printf '%s' "$period" > $cachefile
fi
printf '%s' "$period"