1 files changed, 121 insertions, 0 deletions
diff --git a/internal/thumbnail/cache.go b/internal/thumbnail/cache.go
new file mode 100644
index 0000000..2a1af40
--- /dev/null
+++ b/internal/thumbnail/cache.go
@@ -0,0 +1,121 @@
+package thumbnail
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+type entry struct {
+	VideoPath string    `json:"video_path"`
+	Thumbnail string    `json:"thumbnail"`
+	ModTime   time.Time `json:"mod_time"`
+	Timestamp time.Time `json:"timestamp"`
+}
+
+type Cache struct {
+	entries map[string]entry
+	mu      sync.RWMutex
+	path    string
+}
+
+func NewCache(root string) *Cache {
+	return newCache(root)
+}
+
+func newCache(root string) *Cache {
+	path := filepath.Join(root, cacheFilename)
+	return &Cache{
+		entries: make(map[string]entry),
+		path:    path,
+	}
+}
+
+func (c *Cache) Load() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	data, err := os.ReadFile(c.path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil
+		}
+		return fmt.Errorf("read cache file: %w", err)
+	}
+
+	var loaded []entry
+	if err := json.Unmarshal(data, &loaded); err != nil {
+		return fmt.Errorf("unmarshal cache: %w", err)
+	}
+
+	c.entries = make(map[string]entry, len(loaded))
+	for _, e := range loaded {
+		c.entries[e.VideoPath] = e
+	}
+
+	return nil
+}
+
+func (c *Cache) Lookup(videoPath string, modTime time.Time) (string, bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
+	e, ok := c.entries[videoPath]
+	if !ok {
+		return "", false
+	}
+
+	if !e.ModTime.Equal(modTime) {
+		return "", false
+	}
+
+	if _, err := os.Stat(e.Thumbnail); err != nil {
+		return "", false
+	}
+
+	return e.Thumbnail, true
+}
+
+func (c *Cache) Store(videoPath string, modTime time.Time, thumbnailPath string) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.entries[videoPath] = entry{
+		VideoPath: videoPath,
+		Thumbnail: thumbnailPath,
+		ModTime:   modTime,
+		Timestamp: time.Now(),
+	}
+
+	return c.flush()
+}
+
+func (c *Cache) Remove(videoPath string) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	delete(c.entries, videoPath)
+	return c.flush()
+}
+
+func (c *Cache) flush() error {
+	loaded := make([]entry, 0, len(c.entries))
+	for _, e := range c.entries {
+		loaded = append(loaded, e)
+	}
+
+	data, err := json.MarshalIndent(loaded, "", "  ")
+	if err != nil {
+		return fmt.Errorf("marshal cache: %w", err)
+	}
+
+	if err := os.WriteFile(c.path, data, 0o644); err != nil {
+		return fmt.Errorf("write cache file: %w", err)
+	}
+
+	return nil
+}