feat: add AnswerWebAppQuery

Sets the result of a Web App interaction via
messages.sendWebViewResultMessage, reusing the InlineQueryResult -> tg
InputBotInlineResult conversion. The returned SentWebAppMessage carries the
inline_message_id, encoded with the new inline_message_id codec.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

answer_webapp.go

@@ -0,0 +1,51 @@
+package botapi
+
+import (
+	"context"
+
+	"github.com/gotd/td/tg"
+)
+
+// SentWebAppMessage describes an inline message sent by a Web App on behalf of a
+// user.
+type SentWebAppMessage struct {
+	// InlineMessageID is the identifier of the sent inline message, present only
+	// if the message has a reply markup with at least one callback or inline
+	// query button.
+	InlineMessageID string `json:"inline_message_id,omitempty"`
+}
+
+// AnswerWebAppQuery sets the result of an interaction with a Web App and sends a
+// corresponding message on behalf of the user to the chat from which the query
+// originated. webAppQueryID is the query id from the Web App.
+func (b *Bot) AnswerWebAppQuery(ctx context.Context, webAppQueryID string, result InlineQueryResult) (*SentWebAppMessage, error) {
+	if result == nil {
+		return nil, &Error{Code: 400, Description: "Bad Request: inline query result is nil"}
+	}
+
+	converted, err := result.toTg(ctx, b)
+	if err != nil {
+		return nil, err
+	}
+
+	res, err := b.raw.MessagesSendWebViewResultMessage(ctx, &tg.MessagesSendWebViewResultMessageRequest{
+		BotQueryID: webAppQueryID,
+		Result:     converted,
+	})
+	if err != nil {
+		return nil, asAPIError(err)
+	}
+
+	out := &SentWebAppMessage{}
+
+	if id, ok := res.GetMsgID(); ok {
+		enc, err := encodeInlineMessageID(id)
+		if err != nil {
+			return nil, err
+		}
+
+		out.InlineMessageID = enc
+	}
+
+	return out, nil
+}

answer_webapp_test.go

@@ -0,0 +1,62 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+func TestAnswerWebAppQuery(t *testing.T) {
+	mid := &tg.InputBotInlineMessageID64{DCID: 2, OwnerID: 1, ID: 9, AccessHash: 42}
+
+	sent := &tg.WebViewMessageSent{}
+	sent.SetMsgID(mid)
+
+	inv := newMockInvoker()
+	inv.reply(tg.MessagesSendWebViewResultMessageRequestTypeID, sent)
+
+	result := &InlineQueryResultArticle{
+		ID:                  "r1",
+		Title:               "Title",
+		InputMessageContent: &InputTextMessageContent{MessageText: "hi"},
+	}
+
+	got, err := newMockBot(inv).AnswerWebAppQuery(context.Background(), "wq1", result)
+	if err != nil {
+		t.Fatalf("AnswerWebAppQuery: %v", err)
+	}
+
+	decoded, err := decodeInlineMessageID(got.InlineMessageID)
+	if err != nil {
+		t.Fatalf("decode inline message id %q: %v", got.InlineMessageID, err)
+	}
+
+	if decoded.String() != mid.String() {
+		t.Fatalf("inline message id = %#v, want %#v", decoded, mid)
+	}
+
+	var req tg.MessagesSendWebViewResultMessageRequest
+
+	inv.decode(t, tg.MessagesSendWebViewResultMessageRequestTypeID, &req)
+
+	if req.BotQueryID != "wq1" {
+		t.Fatalf("bot query id = %q", req.BotQueryID)
+	}
+
+	if _, ok := req.Result.(*tg.InputBotInlineResult); !ok {
+		t.Fatalf("result = %#v, want inline result", req.Result)
+	}
+}
+
+func TestAnswerWebAppQueryNilResult(t *testing.T) {
+	inv := newMockInvoker()
+
+	if _, err := newMockBot(inv).AnswerWebAppQuery(context.Background(), "wq1", nil); err == nil {
+		t.Fatal("expected error for nil result")
+	}
+
+	if inv.count() != 0 {
+		t.Fatalf("made %d RPC calls, want 0", inv.count())
+	}
+}