feat(nut): report outage duration and battery % in ntfy

ONBATT records the epoch start time and appends current battery
charge; ONLINE appends battery charge and the total outage duration
(HH:mm:ss) computed from the recorded start, then clears the state.
State lives in /run so it self-clears on reboot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

roles/nut/defaults/main.yml

@@ -61,3 +61,8 @@ nut_ntfy_server: https://ntfy.jokester.fr
 
 # Path of the deployed NOTIFYCMD wrapper.
 nut_notify_script_path: /usr/local/bin/ups-notify
+
+# Where ups-notify records the epoch timestamp of the last ONBATT event, so the
+# ONLINE notification can report total outage duration. Lives under /run so it
+# is cleared on reboot (stale outage state is meaningless after a reboot).
+nut_outage_state_file: /run/ups-notify-outage

roles/nut/templates/ups-notify.sh.j2

@@ -14,15 +14,34 @@ NTFY_TOKEN="{{ nut_ntfy_token }}"
 NTFY_TOKEN=""
 {% endif %}
 
+UPS_NAME="{{ nut_ups_name }}"
+OUTAGE_STATE_FILE="{{ nut_outage_state_file }}"
+
 MESSAGE="${1:-UPS event}"
 EVENT="${NOTIFYTYPE:-UNKNOWN}"
 HOST="$(uname -n)"
 
+# Current battery charge (%) as reported by the UPS. Empty if unavailable.
+battery_charge() {
+  upsc "${UPS_NAME}@localhost" battery.charge 2>/dev/null | head -n1
+}
+
+# Format a duration in whole seconds as HH:mm:ss.
+format_duration() {
+  local total="$1"
+  printf '%02d:%02d:%02d' $((total / 3600)) $(((total % 3600) / 60)) $((total % 60))
+}
+
 case "$EVENT" in
   ONBATT)
+    # Record when line power was lost so ONLINE can report outage duration.
+    date +%s > "$OUTAGE_STATE_FILE" 2>/dev/null || \
+      logger -t ups-notify "Failed to write outage state file $OUTAGE_STATE_FILE"
     TITLE="UPS on battery — $HOST"
     PRIORITY="urgent"
     TAGS="warning,electric_plug"
+    charge="$(battery_charge)"
+    [[ -n "$charge" ]] && MESSAGE="$MESSAGE (battery ${charge}%)"
     ;;
   LOWBATT)
     TITLE="UPS low battery — $HOST"
@@ -38,6 +57,17 @@ case "$EVENT" in
     TITLE="UPS back on line power — $HOST"
     PRIORITY="default"
     TAGS="white_check_mark,zap"
+    charge="$(battery_charge)"
+    [[ -n "$charge" ]] && MESSAGE="$MESSAGE (battery ${charge}%)"
+    if [[ -r "$OUTAGE_STATE_FILE" ]]; then
+      start="$(cat "$OUTAGE_STATE_FILE" 2>/dev/null)"
+      if [[ "$start" =~ ^[0-9]+$ ]]; then
+        elapsed=$(( $(date +%s) - start ))
+        (( elapsed < 0 )) && elapsed=0
+        MESSAGE="$MESSAGE — outage lasted $(format_duration "$elapsed")"
+      fi
+      rm -f "$OUTAGE_STATE_FILE" 2>/dev/null || true
+    fi
     ;;
   COMMBAD|NOCOMM)
     TITLE="UPS communication lost — $HOST"