lib/memfs: add method Watch to MemFS

The Watch method create and start a DirWatcher that ready to be consumed.

This is to simplify watching an existing MemFS instance because the
internal fs inside the DirWatcher is not exported.

2 files changed, 108 insertions, 5 deletions

diff --git a/lib/memfs/memfs.go b/lib/memfs/memfs.go
index 79caae1d..a1cfa331 100644
--- a/lib/memfs/memfs.go
+++ b/lib/memfs/memfs.go
@@ -35,8 +35,10 @@ type MemFS struct {
 	PathNodes *PathNode
 	Root      *Node
 	Opts      *Options
-	incRE     []*regexp.Regexp
-	excRE     []*regexp.Regexp
+	dw        *DirWatcher
+
+	incRE []*regexp.Regexp
+	excRE []*regexp.Regexp
 }
 
 //
@@ -316,9 +318,11 @@ func (mfs *MemFS) Open(path string) (http.File, error) {
 // If child is not part if node's childrens it will return nil.
 //
 func (mfs *MemFS) RemoveChild(parent *Node, child *Node) (removed *Node) {
-	removed = parent.removeChild(child)
-	if removed != nil {
-		mfs.PathNodes.Delete(removed.Path)
+	if parent != nil {
+		removed = parent.removeChild(child)
+		if removed != nil {
+			mfs.PathNodes.Delete(removed.Path)
+		}
 	}
 	return
 }
@@ -402,6 +406,34 @@ func (mfs *MemFS) Update(node *Node, newInfo os.FileInfo) {
 	}
 }
 
+//
+// Watch create and start the DirWatcher that monitor the memfs Root
+// directory.
+// The MemFS will update the tree and node content automatically if the file
+// get deleted or updated.
+// The returned channel nsq is ready to be consumed.
+//
+func (mfs *MemFS) Watch(d time.Duration) (dw *DirWatcher, err error) {
+	var (
+		logp = "Watch"
+	)
+
+	dw = &DirWatcher{
+		fs:      mfs,
+		Delay:   d,
+		Options: *mfs.Opts,
+	}
+
+	err = dw.Start()
+	if err != nil {
+		// There should be no error here, since we already check and
+		// filled the required fields for DirWatcher.
+		return nil, fmt.Errorf("%s: %w", logp, err)
+	}
+
+	return dw, nil
+}
+
 func (mfs *MemFS) createRoot() error {
 	logp := "createRoot"
 
diff --git a/lib/memfs/memfs_example_test.go b/lib/memfs/memfs_example_test.go
index 250d7949..25f257e2 100644
--- a/lib/memfs/memfs_example_test.go
+++ b/lib/memfs/memfs_example_test.go
@@ -2,7 +2,11 @@ package memfs
 
 import (
 	"fmt"
+	"io/ioutil"
 	"log"
+	"os"
+	"path/filepath"
+	"time"
 )
 
 func ExampleNew() {
@@ -87,3 +91,70 @@ func ExampleMemFS_Search() {
 	// Path: /index.css
 	// Snippets: ["body {\n}\n"]
 }
+
+func ExampleMemFS_Watch() {
+	var (
+		mfs  *MemFS
+		dw   *DirWatcher
+		node *Node
+		opts Options
+		ns   NodeState
+		err  error
+	)
+
+	opts.Root, err = ioutil.TempDir("", "memfs_watch")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	defer func() {
+		_ = os.RemoveAll(opts.Root)
+	}()
+
+	mfs, err = New(&opts)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	dw, err = mfs.Watch(200 * time.Millisecond)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Wait for the goroutine on Watch run.
+	time.Sleep(200 * time.Millisecond)
+
+	testFile := filepath.Join(opts.Root, "file")
+	err = os.WriteFile(testFile, []byte("dummy content"), 0700)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	ns = <-dw.C
+	fmt.Printf("State: %s\n", ns.State)
+
+	node, err = mfs.Get("/file")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("Node: %s: %q\n", node.Path, node.Content)
+
+	err = os.Remove(testFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	ns = <-dw.C
+	fmt.Printf("State: %s\n", ns.State)
+
+	node, _ = mfs.Get("/file")
+	fmt.Printf("Node: %s: %v\n", ns.Node.Path, node)
+
+	dw.Stop()
+
+	//Output:
+	//State: FileStateCreated
+	//Node: /file: "dummy content"
+	//State: FileStateDeleted
+	//Node: /file: <nil>
+}