Refactor for readability

internal/store/store.go

@@ -0,0 +1,57 @@
+package store
+
+import (
+	"sync"
+	"time"
+)
+
+const MaxHistoryPoints = 10000
+
+type Sample struct {
+	At    time.Time
+	Value int
+}
+
+type Store struct {
+	mu        sync.RWMutex
+	value     int
+	updatedAt time.Time
+	history   []Sample
+}
+
+func (s *Store) Get() int {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	return s.value
+}
+
+func (s *Store) Set(v int) {
+	s.mu.Lock()
+	s.value = v
+	now := time.Now()
+	s.updatedAt = now
+	s.history = append(s.history, Sample{At: now, Value: v})
+	s.trimHistoryLocked(now)
+	s.mu.Unlock()
+}
+
+func (s *Store) trimHistoryLocked(now time.Time) {
+	cutoff := now.Add(-12 * time.Hour)
+	keep := s.history[:0]
+	for _, point := range s.history {
+		if point.At.After(cutoff) {
+			keep = append(keep, point)
+		}
+	}
+	if len(keep) > MaxHistoryPoints {
+		keep = keep[len(keep)-MaxHistoryPoints:]
+	}
+	s.history = keep
+}
+
+func (s *Store) Snapshot() (int, time.Time, []Sample) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	history := append([]Sample(nil), s.history...)
+	return s.value, s.updatedAt, history
+}

internal/store/store_test.go

@@ -0,0 +1,24 @@
+package store
+
+import (
+	"testing"
+	"time"
+)
+
+func TestTrimHistoryToMaxPoints(t *testing.T) {
+	s := &Store{}
+	base := time.Date(2026, 4, 20, 0, 0, 0, 0, time.UTC)
+	s.history = make([]Sample, 0, MaxHistoryPoints+25)
+	for i := 0; i < MaxHistoryPoints+25; i++ {
+		s.history = append(s.history, Sample{At: base.Add(time.Duration(i) * time.Second), Value: i})
+	}
+
+	s.trimHistoryLocked(base.Add(time.Duration(MaxHistoryPoints+25) * time.Second))
+
+	if got := len(s.history); got != MaxHistoryPoints {
+		t.Fatalf("history length = %d, want %d", got, MaxHistoryPoints)
+	}
+	if s.history[0].Value != 25 {
+		t.Fatalf("oldest retained value = %d, want %d", s.history[0].Value, 25)
+	}
+}