Resolve monitoring PF bot deep links

internal/pf/http.go

@@ -66,9 +66,15 @@ func (s Server) accessMe(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
 	}
+	botUsername := s.App.Cfg.TGBotUsername
+	if botUsername == "" {
+		if resolved, err := s.App.TG.BotUsername(r.Context()); err == nil {
+			botUsername = resolved
+		}
+	}
 	var link *string
-	if s.App.Cfg.TGBotUsername != "" && portalID != "" {
-		v := "https://t.me/" + s.App.Cfg.TGBotUsername + "?start=" + portalID
+	if botUsername != "" && portalID != "" {
+		v := "https://t.me/" + botUsername + "?start=" + portalID
 		link = &v
 	}
 	var command *string
@@ -81,7 +87,7 @@ func (s Server) accessMe(w http.ResponseWriter, r *http.Request) {
 		"portal_user_id":         nullablePlain(portalID),
 		"telegram_linked":        emp != nil && emp.TGChatID != nil && *emp.TGChatID != "",
 		"employee":               emp,
-		"telegram_bot_username":  nullablePlain(s.App.Cfg.TGBotUsername),
+		"telegram_bot_username":  nullablePlain(botUsername),
 		"telegram_start_command": command,
 		"telegram_start_link":    link,
 	})

internal/pf/telegram.go

@@ -9,12 +9,15 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"sync"
 	"time"
 )
 
 type Telegram struct {
 	token    string
 	client   *http.Client
+	mu       sync.Mutex
+	username string
 }
 
 type tgResponse[T any] struct {
@@ -46,6 +49,11 @@ type TGUser struct {
 	LastName  string `json:"last_name"`
 }
 
+type TGBotUser struct {
+	ID       int64  `json:"id"`
+	Username string `json:"username"`
+}
+
 func NewTelegram(token string) *Telegram {
 	return &Telegram{token: token, client: &http.Client{Timeout: 35 * time.Second}}
 }
@@ -54,6 +62,46 @@ func (t *Telegram) Enabled() bool {
 	return strings.TrimSpace(t.token) != ""
 }
 
+func (t *Telegram) BotUsername(ctx context.Context) (string, error) {
+	if !t.Enabled() {
+		return "", nil
+	}
+	t.mu.Lock()
+	if t.username != "" {
+		username := t.username
+		t.mu.Unlock()
+		return username, nil
+	}
+	t.mu.Unlock()
+
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, t.apiURL("getMe"), nil)
+	if err != nil {
+		return "", err
+	}
+	resp, err := t.client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	var out tgResponse[TGBotUser]
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return "", err
+	}
+	if !out.OK {
+		return "", errors.New(out.Description)
+	}
+	username := strings.TrimPrefix(strings.TrimSpace(out.Result.Username), "@")
+	if username == "" {
+		return "", nil
+	}
+	t.mu.Lock()
+	t.username = username
+	t.mu.Unlock()
+	return username, nil
+}
+
 func (t *Telegram) SendMessage(ctx context.Context, chatID string, text string) error {
 	if !t.Enabled() {
 		return nil