From 45ee30fae15022c8bb53039e8222458831298e38 Mon Sep 17 00:00:00 2001
From: Pim van Pelt <pim@ipng.nl>
Date: Wed, 3 Dec 2025 00:17:28 +0100
Subject: [PATCH] Add dryrun flag -n

---
 cmd/s3-genindex/main.go       | 29 +++++++++++++++++++++++------
 internal/indexgen/indexgen.go | 34 +++++++++++++++++++++++++---------
 2 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/cmd/s3-genindex/main.go b/cmd/s3-genindex/main.go
index 4fed48e..a362417 100644
--- a/cmd/s3-genindex/main.go
+++ b/cmd/s3-genindex/main.go
@@ -167,6 +167,24 @@ func generateS3HTML(entries []indexgen.FileEntry, opts *indexgen.Options) error
 		return entries[i].Name < entries[j].Name
 	})
 
+	// Determine output file
+	outputFile := opts.OutputFile
+	if outputFile == "" {
+		outputFile = indexgen.DefaultOutputFile
+	}
+
+	if opts.DryRun {
+		// Dry run mode: show what would be written
+		fmt.Printf("Would write S3 index file: %s\n", outputFile)
+		fmt.Printf("S3 bucket: %s\n", opts.TopDir)
+		fmt.Printf("Objects found: %d\n", len(entries))
+		for _, entry := range entries {
+			fmt.Printf("  object: %s (%s)\n", entry.Name, entry.SizePretty)
+		}
+		return nil
+	}
+
+	// Normal mode: actually write the file
 	// Get the HTML template
 	tmpl := indexgen.GetHTMLTemplate()
 	if tmpl == nil {
@@ -186,12 +204,6 @@ func generateS3HTML(entries []indexgen.FileEntry, opts *indexgen.Options) error
 		Hostname: "S3 Bucket", // Could be improved to show actual endpoint
 	}
 
-	// Determine output file
-	outputFile := opts.OutputFile
-	if outputFile == "" {
-		outputFile = indexgen.DefaultOutputFile
-	}
-
 	// Create output file
 	file, err := os.Create(outputFile)
 	if err != nil {
@@ -217,6 +229,7 @@ func main() {
 	var excludeRegexStr string
 	var directory string
 	var s3URL string
+	var dryRun bool
 
 	// Set defaults
 	opts.DirAppend = true
@@ -227,6 +240,7 @@ func main() {
 	flag.StringVar(&directory, "d", "", "local directory to process")
 	flag.StringVar(&s3URL, "s3", "", "S3 URL to process")
 	flag.StringVar(&opts.Filter, "f", "*", "only include files matching glob")
+	flag.BoolVar(&dryRun, "n", false, "dry run: show what would be written without actually writing")
 	flag.StringVar(&excludeRegexStr, "x", "", "exclude files matching regular expression")
 	flag.BoolVar(&opts.Verbose, "v", false, "verbosely list every processed file")
 
@@ -268,6 +282,9 @@ func main() {
 		}
 	}
 
+	// Set dry run flag
+	opts.DryRun = dryRun
+
 	if s3URL != "" {
 		// Parse S3 URL
 		s3Config, err := parseS3URL(s3URL)
diff --git a/internal/indexgen/indexgen.go b/internal/indexgen/indexgen.go
index 45143fa..e122a4e 100644
--- a/internal/indexgen/indexgen.go
+++ b/internal/indexgen/indexgen.go
@@ -166,6 +166,7 @@ type Options struct {
 	IncludeHidden bool
 	ExcludeRegex  *regexp.Regexp
 	Verbose       bool
+	DryRun        bool
 }
 
 type FileEntry struct {
@@ -194,12 +195,6 @@ func ProcessDir(topDir string, opts *Options) error {
 
 	indexPath := filepath.Join(absPath, opts.OutputFile)
 
-	file, err := os.Create(indexPath)
-	if err != nil {
-		return fmt.Errorf("cannot create file %s: %w", indexPath, err)
-	}
-	defer file.Close()
-
 	dirName := filepath.Base(absPath)
 
 	entries, err := ReadDirEntries(absPath, opts)
@@ -226,9 +221,30 @@ func ProcessDir(topDir string, opts *Options) error {
 		OutputFile: opts.OutputFile,
 	}
 
-	err = GetHTMLTemplate().Execute(file, templateData)
-	if err != nil {
-		return fmt.Errorf("failed to execute template: %w", err)
+	if opts.DryRun {
+		// Dry run mode: show what would be written
+		fmt.Printf("Would write index file: %s\n", indexPath)
+		fmt.Printf("Directory: %s\n", dirName)
+		fmt.Printf("Entries found: %d\n", len(entries))
+		for _, entry := range entries {
+			entryType := "file"
+			if entry.IsDir {
+				entryType = "directory"
+			}
+			fmt.Printf("  %s: %s\n", entryType, entry.Name)
+		}
+	} else {
+		// Normal mode: actually write the file
+		file, err := os.Create(indexPath)
+		if err != nil {
+			return fmt.Errorf("cannot create file %s: %w", indexPath, err)
+		}
+		defer file.Close()
+
+		err = GetHTMLTemplate().Execute(file, templateData)
+		if err != nil {
+			return fmt.Errorf("failed to execute template: %w", err)
+		}
 	}
 
 	if opts.Recursive {