Restructure & rework power management config

system/roles/laptop/power/power-profiles-daemon/default.nix

@@ -0,0 +1,41 @@
+# This sets up power management using auto-cpufreq,
+# alongside with upower and power-profiles-daemon.
+# Together, this provides a complete alternative to TLP
+{ pkgs, lib, config, ...}: let
+  inherit (lib) mkIf;
+  inherit (lib.modules) mkForce;
+  inherit (lib.strings) makeBinPath;
+  deviceType = config.myOptions.device.roles.type;
+  acceptedTypes = ["laptop"];
+in {
+  config = mkIf (builtins.elem deviceType acceptedTypes) {
+    # allows changing system behavior based upon user-selected power profiles
+    # (with `powerprofilesctl` command)
+    services.power-profiles-daemon.enable = true;
+
+    # Power state monitor. Switches power profiles based on charging state.
+    # Plugged in - performance (if available, falls back to balance)
+    # Unplugged - balanced, until below 50%, then power-saver
+    systemd.services."power-monitor" = let
+      dependencies = with pkgs; [
+        coreutils
+        gnugrep
+        power-profiles-daemon
+        inotify-tools
+        jaq
+      ];
+    in {
+      description = "Power Monitoring Service";
+      environment.PATH = mkForce "/run/wrappers/bin:${makeBinPath dependencies}";
+      script = builtins.readFile ./scripts/power_monitor.sh;
+
+      serviceConfig = {
+        Type = "simple";
+        Restart = "on-failure";
+      };
+
+      wants = ["power-profiles-daemon.service"];
+      wantedBy = ["default.target"];
+    };
+  };
+}

system/roles/laptop/power/power-profiles-daemon/scripts/power_monitor.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+
+BAT=$(echo /sys/class/power_supply/BAT*) # only supports single-battery systems
+BAT_STATUS="$BAT/status"
+BAT_CAP="$BAT/capacity"
+
+POWER_SAVE_PERCENT=50 # Enter power-save mode if on bat and below this capacity
+
+HAS_PERFORMANCE="$(powerprofilesctl list | grep "performance" || true)" # the || true ignores grep failing with non-zero code
+
+# monitor loop
+prev=0
+while true; do
+	# read the current state
+	status="$(cat "$BAT_STATUS")"
+	capacity="$(cat "$BAT_CAP")"
+
+	if [[ $status == "Discharging" ]]; then
+		if [[ $capacity -le $POWER_SAVE_PERCENT ]]; then
+			profile="power-saver"
+		else
+			profile="balanced"
+		fi
+	else
+		if [[ -n $HAS_PERFORMANCE ]]; then
+			profile="performance"
+		else
+			profile="balanced"
+		fi
+	fi
+
+	# Set the new profile
+	if [[ $profile != $prev ]]; then
+		echo -en "Setting power profile to ${profile}\n"
+		powerprofilesctl set $profile
+		prev=$profile
+	fi
+
+	# wait for changes in status or capacity files
+	# i.e. for the next power change event
+	inotifywait -qq "$BAT_STATUS" "$BAT_CAP"
+done