chore: add a map in relay controller for storing events

src/controllers/relay.ts

@@ -14,6 +14,7 @@ import { MetadataController, UserRelaysType } from './metadata'
  */
 export class RelayController {
   private static instance: RelayController
+  private events = new Map<string, Event>()
   private debug = true
   public connectedRelays: Relay[] = []
 
@@ -151,6 +152,16 @@ export class RelayController {
     // Wait for all publish operations to complete (either fulfilled or rejected)
     await Promise.allSettled(publishPromises)
 
+    if (publishedOnRelays.length > 0) {
+      // if the event was successfully published to relays then check if it contains the `aTag`
+      // if so, then cache the event
+
+      const aTag = event.tags.find((item) => item[0] === 'a')
+      if (aTag && aTag[1]) {
+        this.events.set(aTag[1], event)
+      }
+    }
+
     // Return the list of relay URLs where the event was published
     return publishedOnRelays
   }
@@ -335,13 +346,35 @@ export class RelayController {
     filter: Filter,
     relays: string[] = []
   ): Promise<Event | null> => {
+    // first check if event is present in cached map then return that
+    // otherwise query relays
+    if (filter['#a']) {
+      const aTag = filter['#a'][0]
+      const cachedEvent = this.events.get(aTag)
+
+      if (cachedEvent) return cachedEvent
+    }
+
     const events = await this.fetchEvents(filter, relays)
 
     // Sort events by creation date in descending order
     events.sort((a, b) => b.created_at - a.created_at)
 
-    // Return the most recent event, or null if no events were received
-    return events[0] || null
+    if (events.length > 0) {
+      const event = events[0]
+
+      // if the aTag was specified in filter then cache the fetched event before returning
+      if (filter['#a']) {
+        const aTag = filter['#a'][0]
+        this.events.set(aTag, event)
+      }
+
+      // return the event
+      return event
+    }
+
+    // return null if event array is empty
+    return null
   }
 
   /**
@@ -358,6 +391,15 @@ export class RelayController {
     hexKey: string,
     userRelaysType: UserRelaysType
   ) => {
+    // first check if event is present in cached map then return that
+    // otherwise query relays
+    if (filter['#a']) {
+      const aTag = filter['#a'][0]
+      const cachedEvent = this.events.get(aTag)
+
+      if (cachedEvent) return cachedEvent
+    }
+
     // Get an instance of the MetadataController, which manages user metadata and relays
     const metadataController = await MetadataController.getInstance()