Add NIP-18 utils

nip18.ts

@@ -0,0 +1,97 @@
+import { Event, finishEvent, Kind, verifySignature } from './event'
+import { EventPointer } from './nip19'
+
+export type RepostEventTemplate = {
+  /**
+   * Pass only non-nip18 tags if you have to.
+   * Nip18 tags ('e' and 'p' tags pointing to the reposted event) will be added automatically.
+   */
+  tags?: string[][]
+
+  /**
+   * Pass an empty string to NOT include the stringified JSON of the reposted event.
+   * Any other content will be ignored and replaced with the stringified JSON of the reposted event.
+   * @default Stringified JSON of the reposted event
+   */
+  content?: '';
+
+  created_at: number
+}
+
+export function finishRepostEvent(
+  t: RepostEventTemplate,
+  reposted: Event<number>,
+  relayUrl: string,
+  privateKey: string,
+): Event<Kind.Repost> {
+  return finishEvent({
+    kind: Kind.Repost,
+    tags: [
+      ...(t.tags ?? []),
+      [ 'e', reposted.id, relayUrl ],
+      [ 'p', reposted.pubkey ],
+    ],
+    content: t.content === '' ? '' : JSON.stringify(reposted),
+    created_at: t.created_at,
+  }, privateKey)
+}
+
+export function getRepostedEventPointer(event: Event<number>): undefined | EventPointer {
+  if (event.kind !== Kind.Repost) {
+    return undefined
+  }
+
+  let lastETag: undefined | string[]
+  let lastPTag: undefined | string[]
+
+  for (let i = event.tags.length - 1; i >= 0 && (lastETag === undefined || lastPTag === undefined); i--) {
+    const tag = event.tags[i]
+    if (tag.length >= 2) {
+      if (tag[0] === 'e' && lastETag === undefined) {
+        lastETag = tag
+      } else if (tag[0] === 'p' && lastPTag === undefined) {
+        lastPTag = tag
+      }
+    }
+  }
+
+  if (lastETag === undefined || lastPTag === undefined) {
+    return undefined
+  }
+
+  return {
+    id: lastETag[1],
+    relays: [ lastETag[2], lastPTag[2] ].filter((x) => x !== undefined),
+    author: lastPTag[1],
+  }
+}
+
+export type GetRepostedEventOptions = {
+  skipVerification?: boolean,
+};
+
+export function getRepostedEvent(event: Event<number>, { skipVerification }: GetRepostedEventOptions = {}): undefined | Event<number> {
+  const pointer = getRepostedEventPointer(event)
+
+  if (pointer === undefined || event.content === '') {
+    return undefined
+  }
+
+  let repostedEvent: undefined | Event<number>
+
+  try {
+    repostedEvent = JSON.parse(event.content) as Event<number>
+  } catch (error) {
+    return undefined
+  }
+
+  if (repostedEvent.id !== pointer.id) {
+    return undefined
+  }
+
+  if (!skipVerification && !verifySignature(repostedEvent)) {
+    return undefined
+  }
+
+  return repostedEvent
+}