Make pipeline take tuples with opts

entrypoint.example.ts

@@ -13,10 +13,10 @@ import {
 const msg = await readStdin();
 
 const result = await pipeline(msg, [
-  noopPolicy,
-  hellthreadPolicy,
-  antiDuplicationPolicy,
-  rateLimitPolicy,
+  [noopPolicy],
+  [hellthreadPolicy, { limit: 100 }],
+  [antiDuplicationPolicy],
+  [rateLimitPolicy],
 ]);
 
 writeStdout(result);

src/pipeline.ts

@@ -1,9 +1,16 @@
 import { InputMessage, OutputMessage, Policy } from './types.ts';
 
+type PolicyTuple<Opts = any> = [policy: Policy<Opts>, opts?: Opts];
+
+type PolicyTuplesRest<T extends PolicyTuple[]> = {
+  [K in keyof T]: PolicyTuple<T[K]>
+}
+
 /** Processes messages through multiple policies, bailing early on rejection. */
-async function pipeline(msg: InputMessage, policies: Policy[]): Promise<OutputMessage> {
-  for (const policy of policies) {
-    const result = await policy(msg);
+async function pipeline<P extends any[]>(msg: InputMessage, policies: [...PolicyTuplesRest<P>]): Promise<OutputMessage> {
+  for (const tuple of policies) {
+    const [policy, opts] = tuple;
+    const result = await policy(msg, opts);
     if (result.action !== 'accept') {
       return result;
     }

src/policies/hellthread-policy.ts

@@ -1,17 +1,21 @@
 import type { Policy } from '../types.ts';
 
-const HELLTHREAD_LIMIT = Number(Deno.env.get('HELLTHREAD_LIMIT') || 100);
+interface Hellthread {
+  limit: number;
+}
 
 /** Reject messages that tag too many participants. */
-const hellthreadPolicy: Policy = (msg) => {
+const hellthreadPolicy: Policy<Hellthread> = (msg, opts) => {
+  const limit = opts?.limit || 100;
+
   if (msg.event.kind === 1) {
     const p = msg.event.tags.filter((tag) => tag[0] === 'p');
 
-    if (p.length > HELLTHREAD_LIMIT) {
+    if (p.length > limit) {
       return {
         id: msg.event.id,
         action: 'reject',
-        msg: `Event rejected due to ${p.length} "p" tags (${HELLTHREAD_LIMIT} is the limit).`,
+        msg: `Event rejected due to ${p.length} "p" tags (${limit} is the limit).`,
       };
     }
   }

src/types.ts

@@ -22,6 +22,6 @@ interface Event<K extends number = number> {
   created_at: number;
 }
 
-type Policy = (msg: InputMessage) => Promise<OutputMessage> | OutputMessage;
+type Policy<Opts = unknown> = (msg: InputMessage, opts?: Opts) => Promise<OutputMessage> | OutputMessage;
 
 export type { Event, InputMessage, OutputMessage, Policy };