[Session] Code cleanup (#3854)

* Split utils into files

* Move reducer to another file

* Write types explicitly

* Remove unnnecessary check

* Move things around a bit

* Move more stuff into agent factories

* Move more stuff into agent

* Fix gates await

* Clarify comments

* Enforce more via types

* Nit

* initSession -> resumeSession

* Protect against races

* Make agent opaque to reducer

* Check using plain condition

src/state/session/moderation.ts

@@ -0,0 +1,50 @@
+import {BSKY_LABELER_DID, BskyAgent} from '@atproto/api'
+
+import {IS_TEST_USER} from '#/lib/constants'
+import {readLabelers} from './agent-config'
+import {SessionAccount} from './types'
+
+export function configureModerationForGuest() {
+  // This global mutation is *only* OK because this code is only relevant for testing.
+  // Don't add any other global behavior here!
+  switchToBskyAppLabeler()
+}
+
+export async function configureModerationForAccount(
+  agent: BskyAgent,
+  account: SessionAccount,
+) {
+  // This global mutation is *only* OK because this code is only relevant for testing.
+  // Don't add any other global behavior here!
+  switchToBskyAppLabeler()
+  if (IS_TEST_USER(account.handle)) {
+    await trySwitchToTestAppLabeler(agent)
+  }
+
+  // The code below is actually relevant to production (and isn't global).
+  const labelerDids = await readLabelers(account.did).catch(_ => {})
+  if (labelerDids) {
+    agent.configureLabelersHeader(
+      labelerDids.filter(did => did !== BSKY_LABELER_DID),
+    )
+  } else {
+    // If there are no headers in the storage, we'll not send them on the initial requests.
+    // If we wanted to fix this, we could block on the preferences query here.
+  }
+}
+
+function switchToBskyAppLabeler() {
+  BskyAgent.configure({appLabelers: [BSKY_LABELER_DID]})
+}
+
+async function trySwitchToTestAppLabeler(agent: BskyAgent) {
+  const did = (
+    await agent
+      .resolveHandle({handle: 'mod-authority.test'})
+      .catch(_ => undefined)
+  )?.data.did
+  if (did) {
+    console.warn('USING TEST ENV MODERATION')
+    BskyAgent.configure({appLabelers: [did]})
+  }
+}