fix: track cache hits and misses in average cache state

steamcache/avgcachestate/avgcachestate.go

@@ -7,9 +7,11 @@ import (
 
 // AvgCacheState is a cache state that averages the last N cache states.
 type AvgCacheState struct {
-	size int
-	avgs []cachestate.CacheState
-	mu   sync.Mutex
+	size   int
+	hits   int
+	misses int
+	avgs   []cachestate.CacheState
+	mu     sync.Mutex
 }
 
 // New creates a new average cache state with the given size.
@@ -42,8 +44,21 @@ func (a *AvgCacheState) Add(cs cachestate.CacheState) {
 
 	a.avgs = append(a.avgs, cs)
 	if len(a.avgs) > a.size {
+		switch a.avgs[0] {
+		case cachestate.CacheStateHit:
+			a.hits--
+		case cachestate.CacheStateMiss:
+			a.misses--
+		}
 		a.avgs = a.avgs[1:]
 	}
+
+	switch cs {
+	case cachestate.CacheStateHit:
+		a.hits++
+	case cachestate.CacheStateMiss:
+		a.misses++
+	}
 }
 
 // Avg returns the average cache state.
@@ -51,13 +66,5 @@ func (a *AvgCacheState) Avg() float64 {
 	a.mu.Lock()
 	defer a.mu.Unlock()
 
-	var hits int
-	for _, cs := range a.avgs {
-		switch cs {
-		case cachestate.CacheStateHit:
-			hits++
-		}
-	}
-
-	return float64(hits) / float64(len(a.avgs))
+	return float64(a.hits) / (float64(a.misses) + 0.0000001)
 }