feat: add AvgCacheState to track average cache hits and misses

steamcache/avgcachestate/avgcachestate.go

@@ -0,0 +1,60 @@
+package avgcachestate
+
+import (
+	"s1d3sw1ped/SteamCache2/vfs/cachestate"
+	"sync"
+)
+
+// AvgCacheState is a cache state that averages the last N cache states.
+type AvgCacheState struct {
+	size int
+	avgs []cachestate.CacheState
+	mu   sync.Mutex
+}
+
+// New creates a new average cache state with the given size.
+func New(size int) *AvgCacheState {
+	return &AvgCacheState{
+		size: size,
+		avgs: make([]cachestate.CacheState, size),
+		mu:   sync.Mutex{},
+	}
+}
+
+// Clear resets the average cache state to zero.
+func (a *AvgCacheState) Clear() {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	a.avgs = make([]cachestate.CacheState, a.size) // zeroed
+}
+
+// Add adds a cache state to the average cache state.
+func (a *AvgCacheState) Add(cs cachestate.CacheState) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	a.avgs = append(a.avgs, cs)
+	if len(a.avgs) > a.size {
+		a.avgs = a.avgs[1:]
+	}
+}
+
+// Avg returns the average cache state.
+func (a *AvgCacheState) Avg() float64 {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	var hits, misses int
+	for _, cs := range a.avgs {
+		switch cs {
+		case cachestate.CacheStateHit:
+			hits++
+		case cachestate.CacheStateMiss:
+			misses++
+		}
+	}
+	total := hits + misses
+
+	return float64(hits) / float64(total)
+}