[Init]

modules/battery_monitor.nix

@@ -0,0 +1,41 @@
+{ config, pkgs, lib, ... }:
+
+
+let conf = config.modules.battery_monitor;
+
+in {
+  options.modules.battery_monitor = with lib; {
+    enable = mkEnableOption "battery_monitor";
+  };
+
+  config = lib.mkIf conf.enable {
+    # Regularly check battery status
+    systemd.user.services.battery_monitor = {
+      wants = [ "display-manager.service" ];
+      wantedBy = [ "graphical-session.target" ];
+      script = ''
+        prev_val=100
+        check () { [[ $1 -ge $val ]] && [[ $1 -lt $prev_val ]]; }
+        notify () {
+          ${pkgs.libnotify}/bin/notify-send -a Battery "$@" \
+            -h "int:value:$val" "Discharging" "$val%, $remaining"
+        }
+        while true; do
+          IFS=: read _ bat0 < <(${pkgs.acpi}/bin/acpi -b)
+          IFS=\ , read status val remaining <<<"$bat0"
+          val=''${val%\%}
+          if [[ $status = Discharging ]]; then
+            echo "$val%, $remaining"
+            if check 30 || check 25 || check 20; then notify
+            elif check 15 || [[ $val -le 10 ]]; then notify -u critical
+            fi
+          fi
+          prev_val=$val
+          # Sleep longer when battery is high to save CPU
+          if [[ $val -gt 30 ]]; then sleep 10m; elif [[ $val -ge 20 ]]; then sleep 5m; else sleep 1m; fi
+        done
+      '';
+    };
+
+  };
+}