Add NIP-10 thread root/reply/mention parsing

nip10.ts

@@ -0,0 +1,73 @@
+import type { Event } from "./event";
+import { EventPointer } from "./nip19";
+
+export type NIP10Result = {
+  /**
+   * Pointer to the root of the thread.
+   */
+  root: EventPointer | undefined;
+
+  /**
+   * Pointer to a "parent" event that parsed event replies to (responded to).
+   */
+  reply: EventPointer | undefined;
+
+  /**
+   * Pointers to events which may or may not be in the reply chain.
+   */
+  mentions: EventPointer[];
+
+  /**
+   * List of pubkeys that are involved in the thread in no particular order.
+   */
+  pubkeys: string[];
+};
+
+export function parse(event: Pick<Event, 'tags'>): NIP10Result {
+  const result: NIP10Result = {
+    reply: undefined,
+    root: undefined,
+    mentions: [],
+    pubkeys: [],
+  };
+
+  const eTags: string[][] = [];
+
+  for (const tag of event.tags) {
+    if (tag[0] === "e" && tag[1]) {
+      eTags.push(tag);
+    }
+
+    if (tag[0] === "p" && tag[1]) {
+      result.pubkeys.push(tag[1]);
+    }
+  }
+
+  for (let eTagIndex = 0; eTagIndex < eTags.length; eTagIndex++) {
+    const eTag = eTags[eTagIndex];
+
+    const [ _, eTagEventId, eTagRelayUrl, eTagMarker ] = eTag as [string, string, undefined | string, undefined | string];
+
+    const eventPointer: EventPointer = {
+      id: eTagEventId,
+      relays: eTagRelayUrl ? [eTagRelayUrl] : [],
+    };
+
+    const isFirstETag = eTagIndex === 0;
+    const isLastETag = eTagIndex === eTags.length - 1;
+
+    if (eTagMarker === 'root' || isFirstETag) {
+      result.root = eventPointer;
+      continue;
+    }
+
+    if (eTagMarker === 'reply' || isLastETag) {
+      result.reply = eventPointer;
+      continue;
+    }
+
+    result.mentions.push(eventPointer);
+  }
+
+  return result;
+}