Add relay package

packages/relay/src/relay.ts

@@ -0,0 +1,56 @@
+import {Emitter, sleep} from "@welshman/lib"
+import {Filter, TrustedEvent, HashedEvent, matchFilters} from "@welshman/util"
+import {Repository} from "./repository.js"
+
+export class LocalRelay<E extends HashedEvent = TrustedEvent> extends Emitter {
+  subs = new Map<string, Filter[]>()
+
+  constructor(readonly repository: Repository<E>) {
+    super()
+  }
+
+  send(type: string, ...message: any[]) {
+    switch (type) {
+      case "EVENT":
+        return this.handleEVENT(message as [E])
+      case "CLOSE":
+        return this.handleCLOSE(message as [string])
+      case "REQ":
+        return this.handleREQ(message as [string, ...Filter[]])
+    }
+  }
+
+  handleEVENT([event]: [E]) {
+    this.repository.publish(event)
+
+    // Callers generally expect async relays
+    void sleep(1).then(() => {
+      this.emit("OK", event.id, true, "")
+
+      if (!this.repository.isDeleted(event)) {
+        for (const [subId, filters] of this.subs.entries()) {
+          if (matchFilters(filters, event)) {
+            this.emit("EVENT", subId, event)
+          }
+        }
+      }
+    })
+  }
+
+  handleCLOSE([subId]: [string]) {
+    this.subs.delete(subId)
+  }
+
+  handleREQ([subId, ...filters]: [string, ...Filter[]]) {
+    this.subs.set(subId, filters)
+
+    // Callers generally expect async relays
+    void sleep(1).then(() => {
+      for (const event of this.repository.query(filters)) {
+        this.emit("EVENT", subId, event)
+      }
+
+      this.emit("EOSE", subId)
+    })
+  }
+}