Handle case sensitive file moves (#1427)

pkg/utils/file.go

@@ -306,3 +306,43 @@ func GetFunscriptPath(path string) string {
 	fn := strings.TrimSuffix(path, ext)
 	return fn + ".funscript"
 }
+
+// IsFsPathCaseSensitive checks the fs of the given path to see if it is case sensitive
+// if the case sensitivity can not be determined false and an error != nil are returned
+func IsFsPathCaseSensitive(path string) (bool, error) {
+	// The case sensitivity of the fs of "path" is determined by case flipping
+	// the first letter rune from the base string of the path
+	// If the resulting flipped path exists then the fs should not be case sensitive
+	// ( we check the file mod time to avoid matching an existing path )
+
+	fi, err := os.Stat(path)
+	if err != nil { // path cannot be stat'd
+		return false, err
+	}
+
+	base := filepath.Base(path)
+	fBase, err := FlipCaseSingle(base)
+	if err != nil { // cannot be case flipped
+		return false, err
+	}
+	i := strings.LastIndex(path, base)
+	if i < 0 { // shouldn't happen
+		return false, fmt.Errorf("could not case flip path %s", path)
+	}
+
+	flipped := []byte(path)
+	for _, c := range []byte(fBase) { // replace base of path with the flipped one ( we need to flip the base or last dir part )
+		flipped[i] = c
+		i++
+	}
+
+	fiCase, err := os.Stat(string(flipped))
+	if err != nil { // cannot stat the case flipped path
+		return true, nil // fs of path should be case sensitive
+	}
+
+	if fiCase.ModTime() == fi.ModTime() { // file path exists and is the same
+		return false, nil // fs of path is not case sensitive
+	}
+	return false, fmt.Errorf("can not determine case sensitivity of path %s", path)
+}