Add a dry run flag

filesystem.go

@@ -0,0 +1,180 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+var filesystem FileSystem = NewRealFileSystem()
+
+// FileSystem abstracts filesystem operations so we can swap implementations
+type FileSystem interface {
+	Remove(path string) error
+	RemoveAll(path string) error
+	MkdirAll(path string, perm os.FileMode) error
+	Symlink(source, target string) error
+	Link(source, target string) error
+	SummaryLines() []string
+	IsDryRun() bool
+}
+
+const (
+	opRemove    = "remove"
+	opRemoveAll = "remove_all"
+	opMkdirAll  = "mkdir_all"
+	opSymlink   = "symlink"
+	opHardlink  = "hardlink"
+)
+
+type operationRecord struct {
+	kind   string
+	source string
+	target string
+	err    error
+	dryRun bool
+}
+
+func (r operationRecord) summaryLine() (string, bool) {
+	if r.kind != opSymlink && r.kind != opHardlink {
+		return "", false
+	}
+
+	kindLabel := "Symlink"
+	if r.kind == opHardlink {
+		kindLabel = "Hardlink"
+	}
+
+	status := "OK"
+	if r.err != nil {
+		status = fmt.Sprintf("FAIL: %v", r.err)
+	} else if r.dryRun {
+		status = "DRY-RUN"
+	}
+
+	return fmt.Sprintf("%s %s -> %s (%s)", kindLabel, r.source, r.target, status), true
+}
+
+type baseFileSystem struct {
+	mu         sync.Mutex
+	operations []operationRecord
+}
+
+func (b *baseFileSystem) addOperation(kind, source, target string, err error, dryRun bool) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.operations = append(b.operations, operationRecord{
+		kind:   kind,
+		source: source,
+		target: target,
+		err:    err,
+		dryRun: dryRun,
+	})
+}
+
+func (b *baseFileSystem) snapshot() []operationRecord {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	ops := make([]operationRecord, len(b.operations))
+	copy(ops, b.operations)
+	return ops
+}
+
+func summarizeOperations(records []operationRecord) []string {
+	var lines []string
+	for _, record := range records {
+		if line, ok := record.summaryLine(); ok {
+			lines = append(lines, line)
+		}
+	}
+	return lines
+}
+
+type realFileSystem struct {
+	baseFileSystem
+}
+
+// NewRealFileSystem returns a filesystem implementation that writes to disk
+func NewRealFileSystem() FileSystem {
+	return &realFileSystem{}
+}
+
+func (fs *realFileSystem) Remove(path string) error {
+	err := os.Remove(path)
+	fs.addOperation(opRemove, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) RemoveAll(path string) error {
+	err := os.RemoveAll(path)
+	fs.addOperation(opRemoveAll, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) MkdirAll(path string, perm os.FileMode) error {
+	err := os.MkdirAll(path, perm)
+	fs.addOperation(opMkdirAll, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) Symlink(source, target string) error {
+	err := os.Symlink(source, target)
+	fs.addOperation(opSymlink, source, target, err, false)
+	return err
+}
+
+func (fs *realFileSystem) Link(source, target string) error {
+	err := os.Link(source, target)
+	fs.addOperation(opHardlink, source, target, err, false)
+	return err
+}
+
+func (fs *realFileSystem) SummaryLines() []string {
+	return summarizeOperations(fs.snapshot())
+}
+
+func (fs *realFileSystem) IsDryRun() bool {
+	return false
+}
+
+type dryRunFileSystem struct {
+	baseFileSystem
+}
+
+// NewDryRunFileSystem returns a filesystem implementation that only records operations
+func NewDryRunFileSystem() FileSystem {
+	return &dryRunFileSystem{}
+}
+
+func (fs *dryRunFileSystem) Remove(path string) error {
+	fs.addOperation(opRemove, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) RemoveAll(path string) error {
+	fs.addOperation(opRemoveAll, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) MkdirAll(path string, perm os.FileMode) error {
+	fs.addOperation(opMkdirAll, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) Symlink(source, target string) error {
+	fs.addOperation(opSymlink, source, target, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) Link(source, target string) error {
+	fs.addOperation(opHardlink, source, target, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) SummaryLines() []string {
+	return summarizeOperations(fs.snapshot())
+}
+
+func (fs *dryRunFileSystem) IsDryRun() bool {
+	return true
+}

instruction.go

@@ -76,12 +76,17 @@ func (instruction *LinkInstruction) Undo() {
 
 	if isSymlink {
 		LogInfo("Removing symlink at %s", FormatTargetPath(instruction.Target))
-		err = os.Remove(instruction.Target)
+		err = filesystem.Remove(instruction.Target)
 		if err != nil {
 			LogError("could not remove symlink at %s; err: %v",
 				FormatTargetPath(instruction.Target), err)
-		}
+		} else {
+			if filesystem.IsDryRun() {
+				LogInfo("[DRY-RUN] Would remove symlink at %s", FormatTargetPath(instruction.Target))
+			} else {
 				LogSuccess("Removed symlink at %s", FormatTargetPath(instruction.Target))
+			}
+		}
 	} else {
 		LogInfo("%s is not a symlink, skipping", FormatTargetPath(instruction.Target))
 	}
@@ -223,7 +228,7 @@ func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 				}
 				if info.Mode().IsRegular() && info.Name() == filepath.Base(instruction.Source) {
 					LogTarget("Overwriting existing file %s", instruction.Target)
-					err := os.Remove(instruction.Target)
+					err := filesystem.Remove(instruction.Target)
 					if err != nil {
 						status <- fmt.Errorf("could not remove existing file %s; err: %v",
 							FormatTargetPath(instruction.Target), err)
@@ -234,7 +239,7 @@ func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 
 			if isSymlink {
 				LogTarget("Removing symlink at %s", instruction.Target)
-				err = os.Remove(instruction.Target)
+				err = filesystem.Remove(instruction.Target)
 				if err != nil {
 					status <- fmt.Errorf("failed deleting %s due to %v",
 						FormatTargetPath(instruction.Target), err)
@@ -247,7 +252,7 @@ func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 					return
 				}
 				LogImportant("Deleting (!!!) %s", instruction.Target)
-				err = os.RemoveAll(instruction.Target)
+				err = filesystem.RemoveAll(instruction.Target)
 				if err != nil {
 					status <- fmt.Errorf("failed deleting %s due to %v",
 						FormatTargetPath(instruction.Target), err)
@@ -263,7 +268,7 @@ func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 
 	targetDir := filepath.Dir(instruction.Target)
 	if _, err := os.Stat(targetDir); os.IsNotExist(err) {
-		err = os.MkdirAll(targetDir, 0755)
+		err = filesystem.MkdirAll(targetDir, 0755)
 		if err != nil {
 			status <- fmt.Errorf("failed creating directory %s due to %v",
 				FormatTargetPath(targetDir), err)
@@ -271,22 +276,36 @@ func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 		}
 	}
 
+	linkType := "symlink"
+	if instruction.Hard {
+		linkType = "hardlink"
+	}
+
 	var err error
 	if instruction.Hard {
-		err = os.Link(instruction.Source, instruction.Target)
+		err = filesystem.Link(instruction.Source, instruction.Target)
 	} else {
-		err = os.Symlink(instruction.Source, instruction.Target)
+		err = filesystem.Symlink(instruction.Source, instruction.Target)
 	}
 	if err != nil {
-		status <- fmt.Errorf("failed creating symlink between %s and %s with error %v",
+		status <- fmt.Errorf("failed creating %s between %s and %s with error %v",
+			linkType,
 			FormatSourcePath(instruction.Source),
 			FormatTargetPath(instruction.Target),
 			err)
 		return
 	}
-	LogSuccess("Created symlink between %s and %s",
+	if filesystem.IsDryRun() {
+		LogInfo("[DRY-RUN] Would create %s between %s and %s",
+			linkType,
 			FormatSourcePath(instruction.Source),
 			FormatTargetPath(instruction.Target))
+	} else {
+		LogSuccess("Created %s between %s and %s",
+			linkType,
+			FormatSourcePath(instruction.Source),
+			FormatTargetPath(instruction.Target))
+	}
 
 	status <- nil
 }

instruction_test.go

@@ -394,6 +394,35 @@ func TestLinkInstruction_RunAsync(t *testing.T) {
 		assert.Contains(t, err.Error(), "files=true")
 		assert.True(t, FileExists(targetDir))
 	})
+
+	t.Run("Dry run does not modify filesystem", func(t *testing.T) {
+		originalFS := filesystem
+		filesystem = NewDryRunFileSystem()
+		defer func() {
+			filesystem = originalFS
+		}()
+
+		target := filepath.Join(testDir, "dryrun-link.txt")
+		instruction := LinkInstruction{
+			Source: srcFile,
+			Target: target,
+			Force:  true,
+			Delete: true,
+		}
+
+		status := make(chan error)
+		go instruction.RunAsync(status)
+
+		err := <-status
+		assert.NoError(t, err)
+		assert.False(t, FileExists(target))
+
+		summary := filesystem.SummaryLines()
+		assert.Equal(t, 1, len(summary))
+		assert.Contains(t, summary[0], "DRY-RUN")
+		assert.Contains(t, summary[0], srcFile)
+		assert.Contains(t, summary[0], target)
+	})
 }
 
 func TestLinkInstruction_Undo(t *testing.T) {

main.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"sync/atomic"
+
 	utils "git.site.quack-lab.dev/dave/cyutils"
 )
 
@@ -27,11 +28,19 @@ func main() {
 	file := flag.String("f", "", "file to read instructions from")
 	debug := flag.Bool("d", false, "debug")
 	undoF := flag.Bool("u", false, "undo")
+	dryRun := flag.Bool("n", false, "dry run (no filesystem changes)")
 	flag.Parse()
 	undo = *undoF
 
 	setupLogging(*debug)
 
+	if *dryRun {
+		filesystem = NewDryRunFileSystem()
+		LogInfo("Dry run mode enabled - no filesystem changes will be made")
+	} else {
+		filesystem = NewRealFileSystem()
+	}
+
 	instructions := make(chan *LinkInstruction, 1000)
 	status := make(chan error)
 
@@ -43,9 +52,11 @@ func main() {
 
 	if instructionsDone == 0 {
 		LogInfo("No instructions were processed")
+		printSummary(filesystem)
 		os.Exit(1)
 	}
 	LogInfo("All done")
+	printSummary(filesystem)
 }
 
 // setupLogging configures logging based on debug flag
@@ -162,6 +173,17 @@ func processInstructions(instructions chan *LinkInstruction) int32 {
 	return instructionsDone
 }
 
+func printSummary(fs FileSystem) {
+	lines := fs.SummaryLines()
+	if len(lines) == 0 {
+		return
+	}
+	LogInfo("Summary:")
+	for _, line := range lines {
+		LogInfo("%s", line)
+	}
+}
+
 func IsPipeInput() bool {
 	info, err := os.Stdin.Stat()
 	if err != nil {