From f2f4dd7b8e7384803cbca6d4ebf7b9c299909153 Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Fri, 24 Mar 2023 20:06:03 -0500
Subject: [PATCH] Allow non-tuple values

---
 entrypoint.example.ts |  6 +++---
 src/pipeline.ts       | 15 +++++++++++----
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/entrypoint.example.ts b/entrypoint.example.ts
index 335e1f8..8ec5df6 100644
--- a/entrypoint.example.ts
+++ b/entrypoint.example.ts
@@ -13,10 +13,10 @@ import {
 const msg = await readStdin();
 
 const result = await pipeline(msg, [
-  [noopPolicy],
+  noopPolicy,
   [hellthreadPolicy, { limit: 100 }],
-  [antiDuplicationPolicy],
-  [rateLimitPolicy],
+  antiDuplicationPolicy,
+  rateLimitPolicy,
 ]);
 
 writeStdout(result);
diff --git a/src/pipeline.ts b/src/pipeline.ts
index 7d8e6c3..7297844 100644
--- a/src/pipeline.ts
+++ b/src/pipeline.ts
@@ -1,15 +1,17 @@
 import { InputMessage, OutputMessage, Policy } from './types.ts';
 
-type PolicyTuple<Opts = any> = [policy: Policy<Opts>, opts?: Opts];
+type PolicyTuple<Opts = unknown> = [policy: Policy<Opts>, opts?: Opts];
 
+// https://stackoverflow.com/a/75806165
+// https://stackoverflow.com/a/54608401
 type PolicyTuplesRest<T extends PolicyTuple[]> = {
-  [K in keyof T]: PolicyTuple<T[K]>
+  [K in keyof T]: PolicyTuple<T[K]> | Policy<T[K]>
 }
 
 /** Processes messages through multiple policies, bailing early on rejection. */
 async function pipeline<P extends any[]>(msg: InputMessage, policies: [...PolicyTuplesRest<P>]): Promise<OutputMessage> {
-  for (const tuple of policies) {
-    const [policy, opts] = tuple;
+  for (const item of policies) {
+    const [policy, opts] = toTuple(item);
     const result = await policy(msg, opts);
     if (result.action !== 'accept') {
       return result;
@@ -23,4 +25,9 @@ async function pipeline<P extends any[]>(msg: InputMessage, policies: [...Policy
   };
 }
 
+/** Coerce item into a tuple if it isn't already. */
+function toTuple<T>(item: PolicyTuple<T> | Policy<T>): PolicyTuple<T> {
+  return typeof item === 'function' ? [item] : item;
+}
+
 export default pipeline;