nip13: add minePow function

nip13.test.ts

@@ -1,7 +1,21 @@
-import { getPow } from './nip13.ts'
+import { getPow, minePow } from './nip13.ts'
 
 test('identifies proof-of-work difficulty', async () => {
   const id = '000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358'
   const difficulty = getPow(id)
   expect(difficulty).toEqual(21)
 })
+
+test('mines POW for an event', async () => {
+  const difficulty = 10
+
+  const event = minePow({
+    kind: 1,
+    tags: [],
+    content: 'Hello, world!',
+    created_at: 0,
+    pubkey: '79c2cae114ea28a981e7559b4fe7854a473521a8d22a66bbab9fa248eb820ff6',
+  }, difficulty)
+
+  expect(getPow(event.id)).toBeGreaterThanOrEqual(difficulty)
+})

nip13.ts

@@ -1,3 +1,5 @@
+import { type UnsignedEvent, type Event, getEventHash } from './event.ts'
+
 /** Get POW difficulty from a Nostr hex ID. */
 export function getPow(hex: string): number {
   let count = 0
@@ -14,3 +16,37 @@ export function getPow(hex: string): number {
 
   return count
 }
+
+/**
+ * Mine an event with the desired POW. This function mutates the event.
+ * Note that this operation is synchronous and should be run in a worker context to avoid blocking the main thread.
+ *
+ * Adapted from Snort: https://git.v0l.io/Kieran/snort/src/commit/4df6c19248184218c4c03728d61e94dae5f2d90c/packages/system/src/pow-util.ts#L14-L36
+ */
+export function minePow<K extends number>(unsigned: UnsignedEvent<K>, difficulty: number): Omit<Event<K>, 'sig'> {
+  let count = 0
+
+  const event = unsigned as Omit<Event<K>, 'sig'>
+  const tag = ['nonce', count.toString(), difficulty.toString()]
+
+  event.tags.push(tag)
+
+  while (true) {
+    const now = Math.floor(new Date().getTime() / 1000)
+
+    if (now !== event.created_at) {
+      count = 0
+      event.created_at = now
+    }
+
+    tag[1] = (++count).toString()
+
+    event.id = getEventHash(event)
+
+    if (getPow(event.id) >= difficulty) {
+      break
+    }
+  }
+
+  return event
+}