implement nip26 delegation.

nip26.ts

@@ -0,0 +1,90 @@
+import * as secp256k1 from '@noble/secp256k1'
+import {sha256} from '@noble/hashes/sha256'
+
+import {Event} from './event'
+import {utf8Encoder} from './utils'
+import {getPublicKey} from './keys'
+
+export type Parameters = {
+  pubkey: string // the key to whom the delegation will be given
+  kind: number | undefined
+  until: number | undefined // delegation will only be valid until this date
+  since: number | undefined // delegation will be valid from this date on
+}
+
+export type Delegation = {
+  from: string // the pubkey who signed the delegation
+  to: string // the pubkey that is allowed to use the delegation
+  cond: string // the string of conditions as they should be included in the event tag
+  sig: string
+}
+
+export function createDelegation(
+  privateKey: string,
+  parameters: Parameters
+): Delegation {
+  let conditions = []
+  if ((parameters.kind || -1) >= 0) conditions.push(`kind=${parameters.kind}`)
+  if (parameters.until) conditions.push(`created_at<${parameters.until}`)
+  if (parameters.since) conditions.push(`created_at>${parameters.since}`)
+  let cond = conditions.join('&')
+
+  if (cond === '')
+    throw new Error('refusing to create a delegation without any conditions')
+
+  let sighash = sha256(
+    utf8Encoder.encode(`nostr:delegation:${parameters.pubkey}:${cond}`)
+  )
+
+  let sig = secp256k1.utils.bytesToHex(
+    secp256k1.schnorr.signSync(sighash, privateKey)
+  )
+
+  return {
+    from: getPublicKey(privateKey),
+    to: parameters.pubkey,
+    cond,
+    sig
+  }
+}
+
+export function getDelegator(event: Event): string | null {
+  // find delegation tag
+  let tag = event.tags.find(tag => tag[0] === 'delegation' && tag.length >= 4)
+  if (!tag) return null
+
+  let pubkey = tag[1]
+  let cond = tag[2]
+  let sig = tag[3]
+
+  // check conditions
+  let conditions = cond.split('&')
+  for (let i = 0; i < conditions.length; i++) {
+    let [key, operator, value] = conditions[i].split(/\b/)
+
+    // the supported conditions are just 'kind' and 'created_at' for now
+    if (key === 'kind' && operator === '=' && event.kind === parseInt(value))
+      continue
+    else if (
+      key === 'created_at' &&
+      operator === '<' &&
+      event.created_at < parseInt(value)
+    )
+      continue
+    else if (
+      key === 'created_at' &&
+      operator === '>' &&
+      event.created_at > parseInt(value)
+    )
+      continue
+    else return null // invalid condition
+  }
+
+  // check signature
+  let sighash = sha256(
+    utf8Encoder.encode(`nostr:delegation:${event.pubkey}:${cond}`)
+  )
+  if (!secp256k1.schnorr.verifySync(sig, sighash, pubkey)) return null
+
+  return pubkey
+}