Handle file rescan (#2951)

* Fire handlers when file updated or moved
* Create galleries as needed
* Clean empty galleries
* Handle cleaning zip folders when path changed
* Fix gallery association on duplicate images
* Re-create missing folder-based galleries

pkg/scene/hash.go

@@ -0,0 +1,19 @@
+package scene
+
+import (
+	"github.com/stashapp/stash/pkg/file"
+	"github.com/stashapp/stash/pkg/models"
+)
+
+// GetHash returns the hash of the file, based on the hash algorithm provided. If
+// hash algorithm is MD5, then Checksum is returned. Otherwise, OSHash is returned.
+func GetHash(f file.File, hashAlgorithm models.HashAlgorithm) string {
+	switch hashAlgorithm {
+	case models.HashAlgorithmMd5:
+		return f.Base().Fingerprints.GetString(file.FingerprintTypeMD5)
+	case models.HashAlgorithmOshash:
+		return f.Base().Fingerprints.GetString(file.FingerprintTypeOshash)
+	default:
+		panic("unknown hash algorithm")
+	}
+}