1 files changed, 167 insertions, 0 deletions
diff --git a/cli/internal/filewatcher/filewatcher.go b/cli/internal/filewatcher/filewatcher.go
new file mode 100644
index 0000000..4f79495
--- /dev/null
+++ b/cli/internal/filewatcher/filewatcher.go
@@ -0,0 +1,167 @@
+// Package filewatcher is used to handle watching for file changes inside the monorepo
+package filewatcher
+
+import (
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/hashicorp/go-hclog"
+	"github.com/pkg/errors"
+	"github.com/vercel/turbo/cli/internal/turbopath"
+)
+
+// _ignores is the set of paths we exempt from file-watching
+var _ignores = []string{".git", "node_modules"}
+
+// FileWatchClient defines the callbacks used by the file watching loop.
+// All methods are called from the same goroutine so they:
+// 1) do not need synchronization
+// 2) should minimize the work they are doing when called, if possible
+type FileWatchClient interface {
+	OnFileWatchEvent(ev Event)
+	OnFileWatchError(err error)
+	OnFileWatchClosed()
+}
+
+// FileEvent is an enum covering the kinds of things that can happen
+// to files that we might be interested in
+type FileEvent int
+
+const (
+	// FileAdded - this is a new file
+	FileAdded FileEvent = iota + 1
+	// FileDeleted - this file has been removed
+	FileDeleted
+	// FileModified - this file has been changed in some way
+	FileModified
+	// FileRenamed - a file's name has changed
+	FileRenamed
+	// FileOther - some other backend-specific event has happened
+	FileOther
+)
+
+var (
+	// ErrFilewatchingClosed is returned when filewatching has been closed
+	ErrFilewatchingClosed = errors.New("Close() has already been called for filewatching")
+	// ErrFailedToStart is returned when filewatching fails to start up
+	ErrFailedToStart = errors.New("filewatching failed to start")
+)
+
+// Event is the backend-independent information about a file change
+type Event struct {
+	Path      turbopath.AbsoluteSystemPath
+	EventType FileEvent
+}
+
+// Backend is the interface that describes what an underlying filesystem watching backend
+// must provide.
+type Backend interface {
+	AddRoot(root turbopath.AbsoluteSystemPath, excludePatterns ...string) error
+	Events() <-chan Event
+	Errors() <-chan error
+	Close() error
+	Start() error
+}
+
+// FileWatcher handles watching all of the files in the monorepo.
+// We currently ignore .git and top-level node_modules. We can revisit
+// if necessary.
+type FileWatcher struct {
+	backend Backend
+
+	logger         hclog.Logger
+	repoRoot       turbopath.AbsoluteSystemPath
+	excludePattern string
+
+	clientsMu sync.RWMutex
+	clients   []FileWatchClient
+	closed    bool
+}
+
+// New returns a new FileWatcher instance
+func New(logger hclog.Logger, repoRoot turbopath.AbsoluteSystemPath, backend Backend) *FileWatcher {
+	excludes := make([]string, len(_ignores))
+	for i, ignore := range _ignores {
+		excludes[i] = filepath.ToSlash(repoRoot.UntypedJoin(ignore).ToString() + "/**")
+	}
+	excludePattern := "{" + strings.Join(excludes, ",") + "}"
+	return &FileWatcher{
+		backend:        backend,
+		logger:         logger,
+		repoRoot:       repoRoot,
+		excludePattern: excludePattern,
+	}
+}
+
+// Close shuts down filewatching
+func (fw *FileWatcher) Close() error {
+	return fw.backend.Close()
+}
+
+// Start recursively adds all directories from the repo root, redacts the excluded ones,
+// then fires off a goroutine to respond to filesystem events
+func (fw *FileWatcher) Start() error {
+	if err := fw.backend.AddRoot(fw.repoRoot, fw.excludePattern); err != nil {
+		return err
+	}
+	if err := fw.backend.Start(); err != nil {
+		return err
+	}
+	go fw.watch()
+	return nil
+}
+
+// AddRoot registers the root a filesystem hierarchy to be watched for changes. Events are *not*
+// fired for existing files when AddRoot is called, only for subsequent changes.
+// NOTE: if it appears helpful, we could change this behavior so that we provide a stream of initial
+// events.
+func (fw *FileWatcher) AddRoot(root turbopath.AbsoluteSystemPath, excludePatterns ...string) error {
+	return fw.backend.AddRoot(root, excludePatterns...)
+}
+
+// watch is the main file-watching loop. Watching is not recursive,
+// so when new directories are added, they are manually recursively watched.
+func (fw *FileWatcher) watch() {
+outer:
+	for {
+		select {
+		case ev, ok := <-fw.backend.Events():
+			if !ok {
+				fw.logger.Info("Events channel closed. Exiting watch loop")
+				break outer
+			}
+			fw.clientsMu.RLock()
+			for _, client := range fw.clients {
+				client.OnFileWatchEvent(ev)
+			}
+			fw.clientsMu.RUnlock()
+		case err, ok := <-fw.backend.Errors():
+			if !ok {
+				fw.logger.Info("Errors channel closed. Exiting watch loop")
+				break outer
+			}
+			fw.clientsMu.RLock()
+			for _, client := range fw.clients {
+				client.OnFileWatchError(err)
+			}
+			fw.clientsMu.RUnlock()
+		}
+	}
+	fw.clientsMu.Lock()
+	fw.closed = true
+	for _, client := range fw.clients {
+		client.OnFileWatchClosed()
+	}
+	fw.clientsMu.Unlock()
+}
+
+// AddClient registers a client for filesystem events
+func (fw *FileWatcher) AddClient(client FileWatchClient) {
+	fw.clientsMu.Lock()
+	defer fw.clientsMu.Unlock()
+	fw.clients = append(fw.clients, client)
+	if fw.closed {
+		client.OnFileWatchClosed()
+	}
+}