Feat: Scheduler

The project name is changing from status-bar to xrsb (for X root
window status bar), so the scheduler is called xrsbs.

The scheduler sends the SIGUSR1 signal to a daemon that is
responsible for maintaining and updating the status (X root window
name property). The daemon will determine which actions to perform
based on the files present in the action directory and remove the files
once the actions are performed, so the scheduler creates action files
just before sending the signal. The scheduler can send one signal to
perform multiple actions by creating multiple action files, and can
create the action file(s) and send the signal immediately,
after some delay, or repeatedly at some interval.

xrsbs

@@ -0,0 +1,106 @@
+#!/bin/bash
+
+USAGE="
+USAGE: xrsb-sched <action> [<when>] [<repeat>]
+
+        action  A comma or space separated list of actions to associate with the
+                update signal.
+
+        when    The integer number of milliseconds to wait before sending the
+                update signal, or one of the following values:
+                  - m to send the update signal at the top of the next minute
+                  - h to send the update signal at the top of the next hour
+                  - d to send the update signal at the top of the next day
+                If not present, the update signal will be sent immediately.
+
+        repeat  If present, the update signal will be sent repeatedly according
+                to <when>.
+
+EXAMPLES:
+
+        If the daemon interprets the actions 'vol' and 'bl' to mean update the
+        volume and backlight statuses, respectively, send a signal to
+        immediately update both of those statuses.
+
+                xsrb-sched 'vol,bl'
+
+        If the daemon interprets the actions 'cpu' and 'mem' to mean update the
+        cpu and memory usage statuses, respectively, send a signal to update
+        both of those statuses every 5 seconds.
+
+                xsrb-sched 'cpu,mem' 5000 1
+
+        If the daemon interprets the actions 'bat' and 'dt' to mean update the
+        battery and date/time statuses, respectively, send a signal to update
+        both of those statuses at the top of every minute.
+
+                xsrb-sched 'bat,dt' m true
+"
+DAEMON=xrsbd
+ACTION_DIR=/tmp/xrsb-action/
+
+# Convert integer milliseconds to floating point seconds
+ms_to_s () {
+  printf '%.3f' "${1}e-3"
+}
+
+# Validate the arguments
+if [[ "$#" -lt 1 || "$#" -gt 3 ]]; then
+  printf '%s' "${USAGE}" 1>&2
+  exit 128
+fi
+
+IFS=', ' read -r -a actions <<< "$1"
+when="${2:-0}"
+repeat="$3"
+
+if [[ ! "${when}" =~ ^[0-9]+|[mhd]$ ]]; then
+  printf 'Invalid argument <when>: %s\n' "${when}" 1>&2
+  exit 128
+fi
+
+# Get the daemon PID so we can send the signal to it later. Getting the PID once
+# here is more efficient than getting it each time in the while loop, but if the
+# daemon is restarted and the PID changes, all subsequent updates will fail.
+daemon_pid="$(pgrep --newest --exact "${DAEMON}")"
+if [[ -z "${daemon_pid}" ]]; then
+  printf 'The daemon %s is not running\n' "${DAEMON}" 1>&2
+  exit 1
+fi
+
+# Send the signal if this is the first run or if repeat is on
+first_run=1
+while [[ "${first_run}" -eq 1 || -n "${repeat}" ]]; do
+  first_run=0
+
+  # Sleep until it's time to send the signal
+  if [[ "${when}" != '0' ]]; then
+    if [[ "${when}" =~ ^[0-9]+$ ]]; then
+      sleep "$(ms_to_s "${when}")"
+    else
+      case "${when}" in
+        m)
+          sleep $((60 - $(date +%S)))
+          ;;
+        h)
+          readarray -t ms < <(date +'%M%n%S')
+          sleep $((3600 - ms[0] * 60 - ms[1]))
+          ;;
+        d)
+          readarray -t hms < <(date +'%H%n%M%n%S')
+          ##sleep $(((24 - hms[0]) * 3600 - hms[1] * 60 - hms[2]))
+          printf '%d\n' $(((24 - hms[0]) * 3600 - hms[1] * 60 - hms[2]))
+          ;;
+      esac
+    fi
+  fi
+
+  # Create the signal data and send the signal to the daemon
+  if [[ "$(ps --no-headers -o '%c' -q "${daemon_pid}")" != "${DAEMON}" ]]; then
+    printf 'The daemon %s is not running\n' "${DAEMON}" 1>&2
+    exit 1
+  fi
+  for action in "${actions[@]}"; do touch "${ACTION_DIR}/${action}"; done
+  kill -SIGUSR1 "${daemon_pid}"
+done
+