feat: move all signal handling to backend plugin

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

plugins/signals-react/README.md

@@ -22,10 +22,15 @@ Example of using the hook:
 ```ts
 import { useSignal } from '@backstage/plugin-signals-react';
 
-const { lastSignal } = useSignal('myplugin:topic');
+const { lastSignal } = useSignal('myplugin:channel');
+
+useEffect(() => {
+  console.log(lastSignal);
+}, [lastSignal]);
 ```
 
-Whenever backend publishes new message to the topic `myplugin:topic`, the lastSignal is changed.
+Whenever backend publishes new message to the channel `myplugin:channel`, the `lastSignal` is changed. The `lastSignal`
+is always initiated with null value before any messages are received from the backend.
 
 ## Using API directly
 
@@ -37,7 +42,7 @@ import { signalsApiRef } from '@backstage/plugin-signals-react';
 
 const signals = useApi(signalsApiRef);
 const { unsubscribe } = signals.subscribe(
-  'myplugin:topic',
+  'myplugin:channel',
   (message: JsonObject) => {
     console.log(message);
   },

plugins/signals-react/api-report.md

@@ -9,7 +9,7 @@ import { JsonObject } from '@backstage/types';
 // @public (undocumented)
 export type SignalApi = {
   subscribe(
-    topic: string,
+    channel: string,
     onMessage: (message: JsonObject) => void,
   ): {
     unsubscribe: () => void;
@@ -20,7 +20,7 @@ export type SignalApi = {
 export const signalApiRef: ApiRef<SignalApi>;
 
 // @public (undocumented)
-export const useSignal: (topic: string) => {
+export const useSignal: (channel: string) => {
   lastSignal: JsonObject | null;
 };
 

plugins/signals-react/src/api/SignalApi.ts

@@ -24,7 +24,7 @@ export const signalApiRef = createApiRef<SignalApi>({
 /** @public */
 export type SignalApi = {
   subscribe(
-    topic: string,
+    channel: string,
     onMessage: (message: JsonObject) => void,
   ): { unsubscribe: () => void };
 };

plugins/signals-react/src/hooks/useSignal.ts

@@ -19,7 +19,7 @@ import { JsonObject } from '@backstage/types';
 import { useEffect, useState } from 'react';
 
 /** @public */
-export const useSignal = (topic: string) => {
+export const useSignal = (channel: string) => {
   const apiHolder = useApiHolder();
   // Use apiHolder instead useApi in case signalApi is not available in the
   // backstage instance this is used
@@ -28,7 +28,7 @@ export const useSignal = (topic: string) => {
   useEffect(() => {
     let unsub: null | (() => void) = null;
     if (signals) {
-      const { unsubscribe } = signals.subscribe(topic, (msg: JsonObject) => {
+      const { unsubscribe } = signals.subscribe(channel, (msg: JsonObject) => {
         setLastSignal(msg);
       });
       unsub = unsubscribe;
@@ -38,7 +38,7 @@ export const useSignal = (topic: string) => {
         unsub();
       }
     };
-  }, [signals, topic]);
+  }, [signals, channel]);
 
   return { lastSignal };
 };