1 files changed, 104 insertions, 0 deletions
diff --git a/internal/app/duration_cache.go b/internal/app/duration_cache.go
new file mode 100644
index 0000000..43172b5
--- /dev/null
+++ b/internal/app/duration_cache.go
@@ -0,0 +1,104 @@
+package app
+
+import (
+	"encoding/json"
+	"errors"
+	"io/fs"
+	"os"
+	"sync"
+	"time"
+)
+
+type cacheEntry struct {
+	DurationSeconds float64 `json:"duration_seconds"`
+	ModTimeUnix     int64   `json:"mod_time_unix"`
+	Size            int64   `json:"size"`
+}
+
+type durationCache struct {
+	path    string
+	entries map[string]cacheEntry
+	mu      sync.Mutex
+	dirty   bool
+}
+
+func newDurationCache(path string) *durationCache {
+	return &durationCache{path: path, entries: make(map[string]cacheEntry)}
+}
+
+func loadDurationCache(path string) (*durationCache, error) {
+	cache := newDurationCache(path)
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return cache, nil
+		}
+		return cache, err
+	}
+	if len(data) == 0 {
+		return cache, nil
+	}
+	if err := json.Unmarshal(data, &cache.entries); err != nil {
+		cache.entries = make(map[string]cacheEntry)
+		return cache, err
+	}
+	return cache, nil
+}
+
+func (c *durationCache) Lookup(path string, info os.FileInfo) (time.Duration, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	entry, ok := c.entries[path]
+	if !ok {
+		return 0, false
+	}
+	if entry.ModTimeUnix != info.ModTime().Unix() || entry.Size != info.Size() {
+		delete(c.entries, path)
+		c.dirty = true
+		return 0, false
+	}
+	if entry.DurationSeconds <= 0 {
+		return 0, false
+	}
+	return time.Duration(entry.DurationSeconds * float64(time.Second)), true
+}
+
+func (c *durationCache) Record(path string, info os.FileInfo, dur time.Duration) error {
+	if c == nil || dur <= 0 {
+		return nil
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.entries == nil {
+		c.entries = make(map[string]cacheEntry)
+	}
+	c.entries[path] = cacheEntry{
+		DurationSeconds: dur.Seconds(),
+		ModTimeUnix:     info.ModTime().Unix(),
+		Size:            info.Size(),
+	}
+	c.dirty = true
+	return nil
+}
+
+func (c *durationCache) Flush() error {
+	if c == nil {
+		return nil
+	}
+	c.mu.Lock()
+	if !c.dirty {
+		c.mu.Unlock()
+		return nil
+	}
+	snapshot := make(map[string]cacheEntry, len(c.entries))
+	for k, v := range c.entries {
+		snapshot[k] = v
+	}
+	c.dirty = false
+	c.mu.Unlock()
+	data, err := json.MarshalIndent(snapshot, "", "  ")
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(c.path, data, 0o644)
+}