Initial project scaffolding

- main.go: CLI entry point with flag parsing
- gitignore.go: .gitignore loading and parsing
- sync.go: initial sync with manifest tracking
- watcher.go: fsnotify-based file watcher with debouncing
- Dockerfile: multi-stage build for Alpine runtime

8 files changed, 414 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bf87c58
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+sourcewatch
+docker-gcc-sync-setup.md
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..eb516c2
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,11 @@
+FROM golang:1.22-alpine AS builder
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -o /sourcewatch .
+
+FROM alpine:3.19
+RUN apk add --no-cache ca-certificates
+COPY --from=builder /sourcewatch /usr/local/bin/sourcewatch
+ENTRYPOINT ["sourcewatch"]
diff --git a/gitignore.go b/gitignore.go
new file mode 100644
index 0000000..f6816bd
--- /dev/null
+++ b/gitignore.go
@@ -0,0 +1,22 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+
+	ignore "github.com/sabhiram/go-gitignore"
+)
+
+func loadGitignore(hostDir string) (*ignore.GitIgnore, error) {
+	gitignorePath := filepath.Join(hostDir, ".gitignore")
+
+	data, err := os.ReadFile(gitignorePath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return ignore.CompileIgnoreLines(), nil
+		}
+		return nil, err
+	}
+
+	return ignore.CompileIgnoreLines(string(data)), nil
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..0c8474f
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,10 @@
+module sourcewatch
+
+go 1.26.4
+
+require (
+	github.com/fsnotify/fsnotify v1.10.1
+	github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06
+)
+
+require golang.org/x/sys v0.13.0 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..0cc9955
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,16 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.10.1 h1:b0/UzAf9yR5rhf3RPm9gf3ehBPpf0oZKIjtpKrx59Ho=
+github.com/fsnotify/fsnotify v1.10.1/go.mod h1:TLheqan6HD6GBK6PrDWyDPBaEV8LspOxvPSjC+bVfgo=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06 h1:OkMGxebDjyw0ULyrTYWeN0UNCCkmCWfjPnIA2W6oviI=
+github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06/go.mod h1:+ePHsJ1keEjQtpvf9HHw0f4ZeJ0TLRsxhunSI2hYJSs=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..345436f
--- /dev/null
+++ b/main.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"flag"
+	"log"
+)
+
+var (
+	hostDir  = flag.String("host", "/host", "Host source directory (read-only)")
+	dataDir  = flag.String("data", "/data", "Data destination directory")
+	verbose  = flag.Bool("verbose", false, "Enable verbose logging")
+	dryRun   = flag.Bool("dry-run", false, "Preview what would be synced without copying")
+)
+
+func main() {
+	flag.Parse()
+	log.SetFlags(log.LstdFlags | log.Lshortfile)
+
+	if *verbose {
+		log.Println("sourcewatch starting...")
+		log.Printf("host: %s, data: %s, dry-run: %v", *hostDir, *dataDir, *dryRun)
+	}
+
+	rules, err := loadGitignore(*hostDir)
+	if err != nil {
+		log.Fatalf("failed to load .gitignore: %v", err)
+	}
+
+	manifest, err := initialSync(*hostDir, *dataDir, rules, *dryRun)
+	if err != nil {
+		log.Fatalf("initial sync failed: %v", err)
+	}
+
+	if err := watch(*hostDir, *dataDir, manifest, rules, *dryRun, *verbose); err != nil {
+		log.Fatalf("watcher failed: %v", err)
+	}
+}
diff --git a/sync.go b/sync.go
new file mode 100644
index 0000000..293f20b
--- /dev/null
+++ b/sync.go
@@ -0,0 +1,106 @@
+package main
+
+import (
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+
+	ignore "github.com/sabhiram/go-gitignore"
+)
+
+type FileMeta struct {
+	Size     int64
+	Mode     os.FileMode
+	Symlink  string
+}
+
+type Manifest struct {
+	Files map[string]FileMeta
+}
+
+func initialSync(hostDir, dataDir string, rules *ignore.GitIgnore, dryRun bool) (*Manifest, error) {
+	manifest := &Manifest{Files: make(map[string]FileMeta)}
+
+	err := filepath.Walk(hostDir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		relPath, err := filepath.Rel(hostDir, path)
+		if err != nil {
+			return err
+		}
+
+		if relPath == "." {
+			return nil
+		}
+
+		if relPath == ".git" || strings.HasPrefix(relPath, ".git"+string(filepath.Separator)) {
+			return filepath.SkipDir
+		}
+
+		if rules.MatchesPath(relPath) {
+			if info.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+
+		destPath := filepath.Join(dataDir, relPath)
+
+		linkTarget := ""
+		if info.Mode()&os.ModeSymlink != 0 {
+			linkTarget, err = os.Readlink(path)
+			if err != nil {
+				return err
+			}
+		}
+
+		meta := FileMeta{
+			Size:    info.Size(),
+			Mode:    info.Mode(),
+			Symlink: linkTarget,
+		}
+		manifest.Files[relPath] = meta
+
+		if dryRun {
+			log.Printf("[dry-run] would sync: %s", relPath)
+			return nil
+		}
+
+		if info.IsDir() {
+			return os.MkdirAll(destPath, info.Mode())
+		}
+
+		if err := os.MkdirAll(filepath.Dir(destPath), 0755); err != nil {
+			return err
+		}
+
+		if linkTarget != "" {
+			return os.Symlink(linkTarget, destPath)
+		}
+
+		return copyFile(path, destPath, info.Mode())
+	})
+
+	return manifest, err
+}
+
+func copyFile(src, dst string, mode os.FileMode) error {
+	srcFile, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcFile.Close()
+
+	dstFile, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
+	if err != nil {
+		return err
+	}
+	defer dstFile.Close()
+
+	_, err = io.Copy(dstFile, srcFile)
+	return err
+}
diff --git a/watcher.go b/watcher.go
new file mode 100644
index 0000000..7b823da
--- /dev/null
+++ b/watcher.go
@@ -0,0 +1,210 @@
+package main
+
+import (
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+	ignore "github.com/sabhiram/go-gitignore"
+)
+
+func watch(hostDir, dataDir string, manifest *Manifest, rules *ignore.GitIgnore, dryRun, verbose bool) error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return err
+	}
+	defer watcher.Close()
+
+	var mu sync.Mutex
+	debounce := make(map[string]*time.Timer)
+
+	if err := addWatchersRecursively(watcher, hostDir, rules); err != nil {
+		return err
+	}
+
+	for {
+		select {
+		case event, ok := <-watcher.Events:
+			if !ok {
+				return nil
+			}
+
+			relPath, err := filepath.Rel(hostDir, event.Name)
+			if err != nil {
+				continue
+			}
+
+			if relPath == ".git" || strings.HasPrefix(relPath, ".git"+string(filepath.Separator)) {
+				continue
+			}
+
+			if rules.MatchesPath(relPath) {
+				continue
+			}
+
+			if verbose {
+				log.Printf("event: %s %s", event.Op, relPath)
+			}
+
+			mu.Lock()
+			if t, exists := debounce[relPath]; exists {
+				t.Stop()
+			}
+			debounce[relPath] = time.AfterFunc(200*time.Millisecond, func() {
+				mu.Lock()
+				delete(debounce, relPath)
+				mu.Unlock()
+				handleEvent(event.Op, hostDir, dataDir, relPath, manifest, rules, dryRun, verbose, watcher)
+			})
+			mu.Unlock()
+
+		case err, ok := <-watcher.Errors:
+			if !ok {
+				return nil
+			}
+			log.Printf("watcher error: %v", err)
+		}
+	}
+}
+
+func handleEvent(op fsnotify.Op, hostDir, dataDir, relPath string, manifest *Manifest, rules *ignore.GitIgnore, dryRun, verbose bool, watcher *fsnotify.Watcher) {
+	destPath := filepath.Join(dataDir, relPath)
+	srcPath := filepath.Join(hostDir, relPath)
+
+	switch {
+	case op&fsnotify.Create != 0:
+		syncCreate(srcPath, destPath, relPath, manifest, dryRun, verbose, watcher)
+
+	case op&fsnotify.Write != 0:
+		syncWrite(srcPath, destPath, relPath, manifest, dryRun, verbose)
+
+	case op&fsnotify.Remove != 0:
+		syncRemove(destPath, relPath, manifest, dryRun, verbose)
+
+	case op&fsnotify.Rename != 0:
+		syncRemove(destPath, relPath, manifest, dryRun, verbose)
+	}
+}
+
+func syncCreate(srcPath, destPath, relPath string, manifest *Manifest, dryRun, verbose bool, watcher *fsnotify.Watcher) {
+	info, err := os.Lstat(srcPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return
+		}
+		log.Printf("error stat %s: %v", relPath, err)
+		return
+	}
+
+	if info.IsDir() {
+		if err := watcher.Add(srcPath); err != nil {
+			log.Printf("error adding watcher for %s: %v", relPath, err)
+		}
+		if dryRun {
+			log.Printf("[dry-run] would create dir: %s", relPath)
+			return
+		}
+		if err := os.MkdirAll(destPath, info.Mode()); err != nil {
+			log.Printf("error creating dir %s: %v", relPath, err)
+		}
+		return
+	}
+
+	linkTarget := ""
+	if info.Mode()&os.ModeSymlink != 0 {
+		linkTarget, _ = os.Readlink(srcPath)
+	}
+
+	meta := FileMeta{
+		Size:    info.Size(),
+		Mode:    info.Mode(),
+		Symlink: linkTarget,
+	}
+	manifest.Files[relPath] = meta
+
+	if dryRun {
+		log.Printf("[dry-run] would sync: %s", relPath)
+		return
+	}
+
+	os.MkdirAll(filepath.Dir(destPath), 0755)
+
+	if linkTarget != "" {
+		if err := os.Symlink(linkTarget, destPath); err != nil {
+			log.Printf("error creating symlink %s: %v", relPath, err)
+		}
+		return
+	}
+
+	if err := copyFile(srcPath, destPath, info.Mode()); err != nil {
+		log.Printf("error copying %s: %v", relPath, err)
+	}
+}
+
+func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun, verbose bool) {
+	info, err := os.Lstat(srcPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return
+		}
+		log.Printf("error stat %s: %v", relPath, err)
+		return
+	}
+
+	meta, exists := manifest.Files[relPath]
+	if exists && meta.Size == info.Size() && meta.Mode == info.Mode() {
+		return
+	}
+
+	manifest.Files[relPath] = FileMeta{
+		Size: info.Size(),
+		Mode: info.Mode(),
+	}
+
+	if dryRun {
+		log.Printf("[dry-run] would update: %s", relPath)
+		return
+	}
+
+	if err := copyFile(srcPath, destPath, info.Mode()); err != nil {
+		log.Printf("error copying %s: %v", relPath, err)
+	}
+}
+
+func syncRemove(destPath, relPath string, manifest *Manifest, dryRun, verbose bool) {
+	delete(manifest.Files, relPath)
+
+	if dryRun {
+		log.Printf("[dry-run] would remove: %s", relPath)
+		return
+	}
+
+	os.Remove(destPath)
+}
+
+func addWatchersRecursively(watcher *fsnotify.Watcher, root string, rules *ignore.GitIgnore) error {
+	return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		relPath, err := filepath.Rel(root, path)
+		if err != nil {
+			return err
+		}
+
+		if relPath == ".git" || strings.HasPrefix(relPath, ".git"+string(filepath.Separator)) {
+			return filepath.SkipDir
+		}
+
+		if info.IsDir() && !rules.MatchesPath(relPath) {
+			return watcher.Add(path)
+		}
+
+		return nil
+	})
+}