feat: implement Go-based mail2couch with working IMAP and CouchDB integration

- Add configuration system with automatic file discovery (current dir, config subdir, user home, XDG config)
- Implement IMAP client with TLS connection, authentication, and mailbox listing
- Add CouchDB integration with database creation and document storage
- Support folder filtering (include/exclude) and date filtering (since parameter)
- Include duplicate detection to prevent re-storing existing messages
- Add comprehensive error handling and logging throughout
- Structure code in clean packages: config, mail, couch
- Application currently uses placeholder messages to test the storage pipeline
- Ready for real IMAP message parsing implementation

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

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

go/main.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"time"
+
+	"mail2couch/config"
+	"mail2couch/couch"
+	"mail2couch/mail"
+)
+
+func main() {
+	cfg, err := config.LoadConfigWithDiscovery()
+	if err != nil {
+		log.Fatalf("Failed to load configuration: %v", err)
+	}
+
+	// Initialize CouchDB client
+	couchClient, err := couch.NewClient(&cfg.CouchDb)
+	if err != nil {
+		log.Fatalf("Failed to create CouchDB client: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	err = couchClient.EnsureDB(ctx, cfg.CouchDb.Database)
+	if err != nil {
+		log.Printf("Could not ensure CouchDB database exists (is it running?): %v", err)
+	} else {
+		fmt.Printf("CouchDB database '%s' is ready.\n", cfg.CouchDb.Database)
+	}
+
+	fmt.Printf("Found %d mail source(s) to process.\n", len(cfg.MailSources))
+	for _, source := range cfg.MailSources {
+		if !source.Enabled {
+			continue
+		}
+
+		fmt.Printf(" - Processing source: %s\n", source.Name)
+		if source.Protocol == "imap" {
+			err := processImapSource(&source, couchClient, cfg.CouchDb.Database)
+			if err != nil {
+				log.Printf("   ERROR: Failed to process IMAP source %s: %v", source.Name, err)
+			}
+		}
+	}
+}
+
+func processImapSource(source *config.MailSource, couchClient *couch.Client, dbName string) error {
+	fmt.Printf("   Connecting to IMAP server: %s:%d\n", source.Host, source.Port)
+	imapClient, err := mail.NewImapClient(source)
+	if err != nil {
+		return fmt.Errorf("failed to connect to IMAP server: %w", err)
+	}
+	defer imapClient.Logout()
+
+	fmt.Println("   IMAP connection successful.")
+
+	mailboxes, err := imapClient.ListMailboxes()
+	if err != nil {
+		return fmt.Errorf("failed to list mailboxes: %w", err)
+	}
+
+	fmt.Printf("   Found %d mailboxes.\n", len(mailboxes))
+
+	// Parse the since date if provided
+	var sinceDate *time.Time
+	if source.MessageFilter.Since != "" {
+		parsed, err := time.Parse("2006-01-02", source.MessageFilter.Since)
+		if err != nil {
+			log.Printf("   WARNING: Invalid since date format '%s', ignoring filter", source.MessageFilter.Since)
+		} else {
+			sinceDate = &parsed
+		}
+	}
+
+	totalMessages := 0
+	totalStored := 0
+
+	// Process each mailbox
+	for _, mailbox := range mailboxes {
+		// Check if this mailbox should be processed based on filters
+		if !imapClient.ShouldProcessMailbox(mailbox, &source.FolderFilter) {
+			fmt.Printf("   Skipping mailbox: %s (filtered)\n", mailbox)
+			continue
+		}
+
+		fmt.Printf("   Processing mailbox: %s\n", mailbox)
+
+		// Retrieve messages from the mailbox
+		messages, err := imapClient.GetMessages(mailbox, sinceDate)
+		if err != nil {
+			log.Printf("   ERROR: Failed to get messages from %s: %v", mailbox, err)
+			continue
+		}
+
+		if len(messages) == 0 {
+			fmt.Printf("     No messages found in %s\n", mailbox)
+			continue
+		}
+
+		fmt.Printf("     Found %d messages in %s\n", len(messages), mailbox)
+		totalMessages += len(messages)
+
+		// Convert messages to CouchDB documents
+		var docs []*couch.MailDocument
+		for _, msg := range messages {
+			doc := couch.ConvertMessage(msg, mailbox)
+			docs = append(docs, doc)
+		}
+
+		// Store messages in CouchDB
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		stored := 0
+		for _, doc := range docs {
+			err := couchClient.StoreMessage(ctx, dbName, doc)
+			if err != nil {
+				log.Printf("     ERROR: Failed to store message %s: %v", doc.ID, err)
+			} else {
+				stored++
+			}
+		}
+		cancel()
+
+		fmt.Printf("     Stored %d/%d messages from %s\n", stored, len(messages), mailbox)
+		totalStored += stored
+	}
+
+	fmt.Printf("   Summary: Processed %d messages, stored %d new messages\n", totalMessages, totalStored)
+	return nil
+}