Add deriveEvent

packages/app/src/collection.ts

@@ -1,6 +1,10 @@
 import {readable, derived, type Readable} from 'svelte/store'
+import {type SubscribeRequest} from "@welshman/net"
 import {indexBy, type Maybe, now} from '@welshman/lib'
-import {withGetter} from '@welshman/store'
+import {getIdFilters} from '@welshman/util'
+import type {TrustedEvent} from '@welshman/util'
+import {withGetter, deriveEvents} from '@welshman/store'
+import {repository, loadOne} from './core'
 import {getFreshness, setFreshness} from './freshness'
 
 export const collection = <T, LoadArgs extends any[]>({
@@ -57,3 +61,21 @@ export const collection = <T, LoadArgs extends any[]>({
 
   return {indexStore, deriveItem, loadItem, getItem}
 }
+
+export const deriveEvent = (idOrAddress: string, request: Partial<SubscribeRequest> = {}) => {
+  let attempted = false
+
+  const filters = getIdFilters([idOrAddress])
+
+  return derived(
+    deriveEvents(repository, {filters, includeDeleted: true}),
+    (events: TrustedEvent[]) => {
+      if (!attempted && events.length === 0) {
+        loadOne({...request, filters})
+        attempted = true
+      }
+
+      return events[0]
+    },
+  )
+}