feat: track battery levels per device

agent/battery/battery.go

@@ -1,6 +1,13 @@
-// Package battery provides functions to check if the system has a battery and return the charge state and percentage.
+// Package battery provides battery information for the host and connected devices.
 package battery
 
+import (
+	"errors"
+	"sort"
+	"strconv"
+	"strings"
+)
+
 const (
 	stateUnknown uint8 = iota
 	stateEmpty
@@ -9,3 +16,55 @@ const (
 	stateDischarging
 	stateIdle
 )
+
+// Battery is a readable battery reported by the operating system.
+type Battery struct {
+	Name                  string
+	Percent               uint8
+	State                 uint8
+	FullChargeCapacity    uint64
+	HasFullChargeCapacity bool
+	System                bool
+}
+
+var errNoBatteries = errors.New("no readable batteries")
+
+// normalizeBatteries supplies stable fallback names and disambiguates duplicates.
+func normalizeBatteries(batteries []Battery) []Battery {
+	nameCounts := make(map[string]int, len(batteries))
+	for i := range batteries {
+		name := strings.TrimSpace(batteries[i].Name)
+		if name == "" {
+			name = "Battery " + strconv.Itoa(i+1)
+		}
+		nameCounts[name]++
+		if nameCounts[name] > 1 {
+			name += " (" + strconv.Itoa(nameCounts[name]) + ")"
+		}
+		batteries[i].Name = name
+	}
+	return batteries
+}
+
+// Primary returns the representative battery. Reported full-charge capacity wins,
+// then system-scoped devices, then name for deterministic ties.
+func Primary(batteries []Battery) (Battery, bool) {
+	if len(batteries) == 0 {
+		return Battery{}, false
+	}
+	ordered := append([]Battery(nil), batteries...)
+	sort.SliceStable(ordered, func(i, j int) bool {
+		a, b := ordered[i], ordered[j]
+		if a.HasFullChargeCapacity != b.HasFullChargeCapacity {
+			return a.HasFullChargeCapacity
+		}
+		if a.HasFullChargeCapacity && a.FullChargeCapacity != b.FullChargeCapacity {
+			return a.FullChargeCapacity > b.FullChargeCapacity
+		}
+		if a.System != b.System {
+			return a.System
+		}
+		return a.Name < b.Name
+	})
+	return ordered[0], true
+}