feat: add MapeoProject.prototype.$createdByToDeviceId (#697)

Turns `createdAt` into `deviceId`.

Partly addresses [#136].

[#136]: #136

src/mapeo-project.js

@@ -558,6 +558,20 @@ export class MapeoProject extends TypedEmitter {
     return this.#roles.getRole(this.#deviceId)
   }
 
+  /**
+   * @param {string} createdBy The `createdBy` value from a document.
+   * @returns {Promise<string>} The device ID for this creator.
+   * @throws When device ID cannot be found.
+   */
+  async $createdByToDeviceId(createdBy) {
+    const discoveryKey = Buffer.from(createdBy, 'hex')
+    const coreId = this.#coreManager
+      .getCoreByDiscoveryKey(discoveryKey)
+      ?.key.toString('hex')
+    if (!coreId) throw new Error('NotFound')
+    return this.#coreOwnership.getOwner(coreId)
+  }
+
   /**
    * Replicate a project to a @hyperswarm/secret-stream. Invites will not
    * function because the RPC channel is not connected for project replication,

test-e2e/created_by_to_device_id.js

@@ -0,0 +1,53 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+import {
+  connectPeers,
+  createManagers,
+  invite,
+  waitForPeers,
+  waitForSync,
+} from './utils.js'
+
+test('$createdByToDeviceId', async (t) => {
+  const managers = await createManagers(2, t)
+
+  const disconnectPeers = connectPeers(managers)
+  t.after(disconnectPeers)
+  await waitForPeers(managers)
+
+  const [creator, member] = managers
+  const projectId = await creator.createProject({ name: 'mapeo' })
+
+  await invite({
+    invitor: creator,
+    invitees: [member],
+    projectId,
+  })
+
+  const projects = await Promise.all(
+    managers.map((m) => m.getProject(projectId))
+  )
+  const [creatorProject, memberProject] = projects
+
+  creatorProject.$sync.start()
+  memberProject.$sync.start()
+
+  const observation = await creatorProject.observation.create({
+    schemaName: 'observation',
+    attachments: [],
+    tags: {},
+    refs: [],
+    metadata: {},
+  })
+
+  await waitForSync(projects, 'full')
+
+  assert.equal(
+    await creatorProject.$createdByToDeviceId(observation.createdBy),
+    creator.deviceId
+  )
+  assert.equal(
+    await memberProject.$createdByToDeviceId(observation.createdBy),
+    creator.deviceId
+  )
+})