feat: allow defining signal type

this makes using especially the frontend API much usable as the signal
can be typed instead having plain json object to play around with.

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

plugins/signals-node/src/DefaultSignalService.ts

@@ -16,6 +16,7 @@
 import { EventBroker } from '@backstage/plugin-events-node';
 import { SignalPayload, SignalServiceOptions } from './types';
 import { SignalService } from './SignalService';
+import { JsonObject } from '@backstage/types';
 
 /** @public */
 export class DefaultSignalService implements SignalService {
@@ -31,12 +32,12 @@ export class DefaultSignalService implements SignalService {
   }
 
   /**
-   * Publishes a message to user refs to specific topic
-   * @param recipients - string or array of user ref strings to publish message to
-   * @param topic - message topic
-   * @param message - message to publish
+   * Publishes a signal to user refs to specific topic
+   * @param signal - Signal to publish
    */
-  async publish(signal: SignalPayload) {
+  async publish<SignalType extends JsonObject = JsonObject>(
+    signal: SignalPayload<SignalType>,
+  ) {
     await this.eventBroker?.publish({
       topic: 'signals',
       eventPayload: signal,

plugins/signals-node/src/SignalService.ts

@@ -14,11 +14,15 @@
  * limitations under the License.
  */
 import { SignalPayload } from './types';
+import { JsonObject } from '@backstage/types';
 
 /** @public */
 export interface SignalService {
   /**
-   * Publishes a message to user refs to specific topic
+   * Publishes a signal to user refs to specific topic
+   * @param signal - Signal to publish
    */
-  publish(signal: SignalPayload): Promise<void>;
+  publish<SignalType extends JsonObject = JsonObject>(
+    signal: SignalPayload<SignalType>,
+  ): Promise<void>;
 }

plugins/signals-node/src/types.ts

@@ -24,8 +24,8 @@ export type SignalServiceOptions = {
 };
 
 /** @public */
-export type SignalPayload = {
+export type SignalPayload<SignalType extends JsonObject = JsonObject> = {
   recipients: string[] | string | null;
   channel: string;
-  message: JsonObject;
+  message: SignalType;
 };