feat: add --dry-run mode to Go implementation

Add comprehensive dry-run functionality that allows users to test their
configuration without making any changes to CouchDB. The feature includes:

- New --dry-run/-n command line flag with help and completion support
- Skips all CouchDB write operations while preserving IMAP operations
- Provides detailed logging of what would be done in normal mode
- Shows sample message data and metadata updates that would occur
- Maintains all existing functionality when dry-run is disabled

This addresses the critical usability need identified in ANALYSIS.md for
safe configuration testing before making database changes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

go/config/config.go

@@ -86,6 +86,7 @@ func (ms *MailSource) IsArchiveMode() bool {
 type CommandLineArgs struct {
 	ConfigPath  string
 	MaxMessages int
+	DryRun      bool
 }
 
 // ParseCommandLine parses command line arguments using GNU-style options
@@ -95,6 +96,7 @@ func ParseCommandLine() *CommandLineArgs {
 	// Define long options with -- and short options with -
 	pflag.StringVarP(&args.ConfigPath, "config", "c", "", "Path to configuration file")
 	pflag.IntVarP(&args.MaxMessages, "max-messages", "m", 0, "Maximum number of messages to process per mailbox per run (0 = no limit)")
+	pflag.BoolVarP(&args.DryRun, "dry-run", "n", false, "Show what would be done without making any changes")
 
 	// Add utility options
 	pflag.BoolP("help", "h", false, "Show help message")
@@ -146,7 +148,7 @@ _%s_completions() {
 
     if [[ $cur == -* ]]; then
         # Complete with available options
-        local opts="-c --config -m --max-messages -h --help --generate-bash-completion"
+        local opts="-c --config -m --max-messages -n --dry-run -h --help --generate-bash-completion"
         COMPREPLY=($(compgen -W "$opts" -- "$cur"))
         return
     fi
@@ -217,5 +219,8 @@ func LoadConfigWithDiscovery(args *CommandLineArgs) (*Config, error) {
 	} else {
 		fmt.Printf("Maximum messages per mailbox: unlimited\n")
 	}
+	if args.DryRun {
+		fmt.Printf("DRY-RUN MODE: No changes will be made to CouchDB\n")
+	}
 	return LoadConfig(configPath)
 }

go/main.go

@@ -19,11 +19,15 @@ func main() {
 		log.Fatalf("Failed to load configuration: %v", err)
 	}
 
-	// Initialize CouchDB client
+	// Initialize CouchDB client (skip in dry-run mode)
-	couchClient, err := couch.NewClient(&cfg.CouchDb)
+	var couchClient *couch.Client
+	if !args.DryRun {
+		var err error
+		couchClient, err = couch.NewClient(&cfg.CouchDb)
 		if err != nil {
 			log.Fatalf("Failed to create CouchDB client: %v", err)
 		}
+	}
 
 	fmt.Printf("Found %d mail source(s) to process.\n", len(cfg.MailSources))
 	for _, source := range cfg.MailSources {
@@ -34,7 +38,8 @@ func main() {
 		// Generate per-account database name
 		dbName := couch.GenerateAccountDBName(source.Name, source.User)
 
-		// Ensure the account-specific database exists
+		// Ensure the account-specific database exists (skip in dry-run mode)
+		if !args.DryRun {
 			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 			err = couchClient.EnsureDB(ctx, dbName)
 			cancel()
@@ -45,10 +50,13 @@ func main() {
 			} else {
 				fmt.Printf("CouchDB database '%s' is ready for account: %s\n", dbName, source.Name)
 			}
+		} else {
+			fmt.Printf("DRY-RUN: Would ensure CouchDB database '%s' exists for account: %s\n", dbName, source.Name)
+		}
 
 		fmt.Printf(" - Processing source: %s\n", source.Name)
 		if source.Protocol == "imap" {
-			err := processImapSource(&source, couchClient, dbName, args.MaxMessages)
+			err := processImapSource(&source, couchClient, dbName, args.MaxMessages, args.DryRun)
 			if err != nil {
 				log.Printf("   ERROR: Failed to process IMAP source %s: %v", source.Name, err)
 			}
@@ -56,7 +64,7 @@ func main() {
 	}
 }
 
-func processImapSource(source *config.MailSource, couchClient *couch.Client, dbName string, maxMessages int) error {
+func processImapSource(source *config.MailSource, couchClient *couch.Client, dbName string, maxMessages int, dryRun bool) error {
 	fmt.Printf("   Connecting to IMAP server: %s:%d\n", source.Host, source.Port)
 	imapClient, err := mail.NewImapClient(source)
 	if err != nil {
@@ -92,14 +100,18 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 	for _, mailbox := range mailboxes {
 		fmt.Printf("   Processing mailbox: %s (mode: %s)\n", mailbox, source.Mode)
 
-		// Get sync metadata to determine incremental sync date
+		// Get sync metadata to determine incremental sync date (skip in dry-run mode)
+		var syncMetadata *couch.SyncMetadata
+		if !dryRun {
 			syncCtx, syncCancel := context.WithTimeout(context.Background(), 10*time.Second)
-		syncMetadata, err := couchClient.GetSyncMetadata(syncCtx, dbName, mailbox)
+			var err error
+			syncMetadata, err = couchClient.GetSyncMetadata(syncCtx, dbName, mailbox)
 			syncCancel()
 			if err != nil {
 				log.Printf("   ERROR: Failed to get sync metadata for %s: %v", mailbox, err)
 				continue
 			}
+		}
 
 		// Determine the since date for incremental sync
 		var sinceDate *time.Time
@@ -113,10 +125,14 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 			sinceDate = configSinceDate
 			if sinceDate != nil {
 				fmt.Printf("     First sync since: %s (from config)\n", sinceDate.Format("2006-01-02"))
+			} else {
+				if dryRun {
+					fmt.Printf("     DRY-RUN: Would perform first full sync (no date filter)\n")
 				} else {
 					fmt.Printf("     First full sync (no date filter)\n")
 				}
 			}
+		}
 
 		// Retrieve messages from the mailbox
 		messages, currentUIDs, err := imapClient.GetMessages(mailbox, sinceDate, maxMessages, &source.MessageFilter)
@@ -125,7 +141,8 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 			continue
 		}
 
-		// Perform sync/archive logic
+		// Perform sync/archive logic (skip in dry-run mode)
+		if !dryRun {
 			mailboxSyncCtx, mailboxSyncCancel := context.WithTimeout(context.Background(), 30*time.Second)
 			err = couchClient.SyncMailbox(mailboxSyncCtx, dbName, mailbox, currentUIDs, source.IsSyncMode())
 			mailboxSyncCancel()
@@ -133,6 +150,10 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 				log.Printf("   ERROR: Failed to sync mailbox %s: %v", mailbox, err)
 				continue
 			}
+		} else {
+			fmt.Printf("     DRY-RUN: Would sync mailbox %s with %d current UIDs (mode: %s)\n", 
+				mailbox, len(currentUIDs), source.Mode)
+		}
 
 		if len(messages) == 0 {
 			fmt.Printf("     No new messages found in %s\n", mailbox)
@@ -149,9 +170,10 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 			docs = append(docs, doc)
 		}
 
-		// Store messages in CouchDB with attachments
+		// Store messages in CouchDB with attachments (skip in dry-run mode)
-		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 		stored := 0
+		if !dryRun {
+			ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 			for i, doc := range docs {
 				err := couchClient.StoreMessage(ctx, dbName, doc, messages[i])
 				if err != nil {
@@ -161,11 +183,19 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 				}
 			}
 			cancel()
-
 			fmt.Printf("     Stored %d/%d messages from %s\n", stored, len(messages), mailbox)
+		} else {
+			stored = len(messages) // In dry-run, assume all would be stored
+			fmt.Printf("     DRY-RUN: Would store %d messages from %s\n", len(messages), mailbox)
+			// Show sample of what would be stored
+			if len(docs) > 0 {
+				fmt.Printf("     DRY-RUN: Sample message ID: %s (Subject: %s)\n", 
+					docs[0].ID, docs[0].Subject)
+			}
+		}
 		totalStored += stored
 
-		// Update sync metadata after successful processing
+		// Update sync metadata after successful processing (skip in dry-run mode)
 		if len(messages) > 0 {
 			// Find the highest UID processed
 			var maxUID uint32
@@ -175,6 +205,7 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 				}
 			}
 
+			if !dryRun {
 				// Create/update sync metadata
 				newMetadata := &couch.SyncMetadata{
 					Mailbox:        mailbox,
@@ -192,9 +223,16 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 				} else {
 					fmt.Printf("     Updated sync metadata (last UID: %d)\n", maxUID)
 				}
+			} else {
+				fmt.Printf("     DRY-RUN: Would update sync metadata (last UID: %d, %d messages)\n", maxUID, stored)
+			}
 		}
 	}
 
+	if dryRun {
+		fmt.Printf("   DRY-RUN Summary: Found %d messages, would store %d messages\n", totalMessages, totalStored)
+	} else {
 		fmt.Printf("   Summary: Processed %d messages, stored %d new messages\n", totalMessages, totalStored)
+	}
 	return nil
 }