DirTree.Prune: deletes several directories

fs/walk.go

@@ -250,6 +250,87 @@ func (dt DirTree) Dirs() (dirNames []string) {
 	return dirNames
 }
 
+// Prune remove directories from a directory tree. dirNames contains
+// all directories to remove as keys, with true as values. dirNames
+// will be modified in the function.
+func (dt DirTree) Prune(dirNames map[string]bool) error {
+	// We use map[string]bool to avoid recursion (and potential
+	// stack exhaustion).
+
+	// First we need delete directories from their parents.
+	for dName, remove := range dirNames {
+		if !remove {
+			// Currently all values should be
+			// true, therefore this should not
+			// happen. But this makes function
+			// more predictable.
+			Infof(dName, "Directory in the map for prune, but the value is false")
+			continue
+		}
+		if dName == "" {
+			// if dName is root, do nothing (no parent exist)
+			continue
+		}
+		parent := parentDir(dName)
+		// It may happen that dt does not have a dName key,
+		// since directory was excluded based on a filter. In
+		// such case the loop will be skipped.
+		for i, entry := range dt[parent] {
+			switch x := entry.(type) {
+			case Directory:
+				if x.Remote() == dName {
+					// the slice is not sorted yet
+					// to delete item
+					// a) replace it with the last one
+					dt[parent][i] = dt[parent][len(dt[parent])-1]
+					// b) remove last
+					dt[parent] = dt[parent][:len(dt[parent])-1]
+					// we modify a slice within a loop, but we stop
+					// iterating immediately
+					break
+				}
+			case Object:
+				// do nothing
+			default:
+				return errors.Errorf("unknown object type %T", entry)
+
+			}
+		}
+	}
+
+	for len(dirNames) > 0 {
+		// According to golang specs, if new keys were added
+		// during range iteration, they may be skipped.
+		for dName, remove := range dirNames {
+			if !remove {
+				Infof(dName, "Directory in the map for prune, but the value is false")
+				continue
+			}
+			// First, add all subdirectories to dirNames.
+
+			// It may happen that dt[dName] does not exist.
+			// If so, the loop will be skipped.
+			for _, entry := range dt[dName] {
+				switch x := entry.(type) {
+				case Directory:
+					excludeDir := x.Remote()
+					dirNames[excludeDir] = true
+				case Object:
+					// do nothing
+				default:
+					return errors.Errorf("unknown object type %T", entry)
+
+				}
+			}
+			// Then remove current directory from DirTree
+			delete(dt, dName)
+			// and from dirNames
+			delete(dirNames, dName)
+		}
+	}
+	return nil
+}
+
 // String emits a simple representation of the DirTree
 func (dt DirTree) String() string {
 	out := new(bytes.Buffer)