feat: create commands_clients.go and add ClientsCommand with complete logic

Create separate file for clients command handling to improve code organization.
Add ClientsCommand struct with ListClients method that includes all original logic:
service status checks, HTTP requests, source mapping, metrics handling, and table
formatting. Includes InitClientsCmd function that creates proper command hierarchy
with clients parent command and list sub-command.

cmd/cli/commands_clients.go

@@ -0,0 +1,140 @@
+package cli
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/kardianos/service"
+	"github.com/olekukonko/tablewriter"
+	"github.com/spf13/cobra"
+
+	"github.com/Control-D-Inc/ctrld/internal/clientinfo"
+)
+
+// ClientsCommand handles clients-related operations
+type ClientsCommand struct {
+	controlClient *controlClient
+}
+
+// NewClientsCommand creates a new clients command handler
+func NewClientsCommand() (*ClientsCommand, error) {
+	dir, err := socketDir()
+	if err != nil {
+		return nil, fmt.Errorf("failed to find ctrld home dir: %w", err)
+	}
+
+	cc := newControlClient(filepath.Join(dir, ctrldControlUnixSock))
+	return &ClientsCommand{
+		controlClient: cc,
+	}, nil
+}
+
+// ListClients lists all connected clients
+func (cc *ClientsCommand) ListClients(cmd *cobra.Command, args []string) error {
+	// Check service status first
+	sm, err := NewServiceManager()
+	if err != nil {
+		return err
+	}
+
+	status, err := sm.Status()
+	if errors.Is(err, service.ErrNotInstalled) {
+		mainLog.Load().Warn().Msg("service not installed")
+		return nil
+	}
+	if status == service.StatusStopped {
+		mainLog.Load().Warn().Msg("service is not running")
+		return nil
+	}
+
+	resp, err := cc.controlClient.post(listClientsPath, nil)
+	if err != nil {
+		return fmt.Errorf("failed to get clients: %w", err)
+	}
+	defer resp.Body.Close()
+
+	var clients []*clientinfo.Client
+	if err := json.NewDecoder(resp.Body).Decode(&clients); err != nil {
+		return fmt.Errorf("failed to decode clients result: %w", err)
+	}
+
+	map2Slice := func(m map[string]struct{}) []string {
+		s := make([]string, 0, len(m))
+		for k := range m {
+			if k == "" { // skip empty source from output.
+				continue
+			}
+			s = append(s, k)
+		}
+		sort.Strings(s)
+		return s
+	}
+
+	// If metrics is enabled, server set this for all clients, so we can check only the first one.
+	// Ideally, we may have a field in response to indicate that query count should be shown, but
+	// it would break earlier version of ctrld, which only look list of clients in response.
+	withQueryCount := len(clients) > 0 && clients[0].IncludeQueryCount
+	data := make([][]string, len(clients))
+	for i, c := range clients {
+		row := []string{
+			c.IP.String(),
+			c.Hostname,
+			c.Mac,
+			strings.Join(map2Slice(c.Source), ","),
+		}
+		if withQueryCount {
+			row = append(row, strconv.FormatInt(c.QueryCount, 10))
+		}
+		data[i] = row
+	}
+
+	table := tablewriter.NewWriter(os.Stdout)
+	headers := []string{"IP", "Hostname", "Mac", "Discovered"}
+	if withQueryCount {
+		headers = append(headers, "Queries")
+	}
+	table.SetHeader(headers)
+	table.SetAutoFormatHeaders(false)
+	table.AppendBulk(data)
+	table.Render()
+
+	return nil
+}
+
+// InitClientsCmd creates the clients command with proper logic
+func InitClientsCmd() *cobra.Command {
+	listClientsCmd := &cobra.Command{
+		Use:   "list",
+		Short: "List clients that ctrld discovered",
+		Args:  cobra.NoArgs,
+		PreRun: func(cmd *cobra.Command, args []string) {
+			checkHasElevatedPrivilege()
+		},
+		RunE: func(cmd *cobra.Command, args []string) error {
+			cc, err := NewClientsCommand()
+			if err != nil {
+				return err
+			}
+			return cc.ListClients(cmd, args)
+		},
+	}
+
+	clientsCmd := &cobra.Command{
+		Use:   "clients",
+		Short: "Manage clients",
+		Args:  cobra.OnlyValidArgs,
+		ValidArgs: []string{
+			listClientsCmd.Use,
+		},
+	}
+	clientsCmd.AddCommand(listClientsCmd)
+	rootCmd.AddCommand(clientsCmd)
+
+	return clientsCmd
+}