From d0a05700e4ba0ef7f419aade22258c5e34e2dbe9 Mon Sep 17 00:00:00 2001
From: Vitaly Tomilov <vitaly-t@users.noreply.github.com>
Date: Sat, 3 Aug 2024 16:26:56 +0100
Subject: [PATCH] refactoring timeout + tests

---
 src/ops/async/delay.ts    |  7 ++++++-
 src/ops/timeout.ts        | 16 +++++++--------
 test/ops/timeout/async.ts | 42 +++++++++++++++++++++++++++++----------
 3 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/src/ops/async/delay.ts b/src/ops/async/delay.ts
index e8f99ec0..2e66df35 100644
--- a/src/ops/async/delay.ts
+++ b/src/ops/async/delay.ts
@@ -2,7 +2,7 @@ import {$A, Operation, IterationState} from '../../types';
 import {createOperation, throwOnSync} from '../../utils';
 
 /**
- * Delays each value by the specified timeout.
+ * Delays each value by the specified timeout (including the first one).
  * When the timeout is a negative number, no delay added.
  *
  * ```ts
@@ -20,6 +20,11 @@ import {createOperation, throwOnSync} from '../../utils';
  * }
  * ```
  *
+ * Note that passing in `timeout = 0`, or returning the same from the callback,
+ * still uses the `timeout` function, just like `setTimeout(0)`, which can be used
+ * for throttling. In order to fully deactivate it, you need to pass in a negative
+ * `timeout` value.
+ *
  * @throws `Error: 'Operator "delay" requires asynchronous pipeline'` when used inside a synchronous pipeline.
  *
  * @see
diff --git a/src/ops/timeout.ts b/src/ops/timeout.ts
index eac0ceed..fc58e6cb 100644
--- a/src/ops/timeout.ts
+++ b/src/ops/timeout.ts
@@ -76,13 +76,13 @@ function timeoutSync<T>(
     ms: number,
     cb?: (count: number) => void
 ): Iterable<T> {
+    if (ms < 0) {
+        // timeout is inactive, reuse the source iterable instead:
+        return iterable;
+    }
     return {
         [$S](): Iterator<T> {
             const i = iterable[$S]();
-            if (ms < 0) {
-                // timeout is inactive;
-                return i;
-            }
             let count = 0; // number of items processed
             let start: number;
             let done = false;
@@ -113,13 +113,13 @@ function timeoutAsync<T>(
     ms: number,
     cb?: (index: number) => void
 ): AsyncIterable<T> {
+    if (ms < 0) {
+        // timeout is inactive, reuse the source iterable instead:
+        return iterable;
+    }
     return {
         [$A](): AsyncIterator<T> {
             const i = iterable[$A]();
-            if (ms < 0) {
-                // timeout is inactive;
-                return i;
-            }
             let count = 0; // number of items processed
             let done = false;
             const resolutions: ((res: IteratorResult<any>) => void)[] = [];
diff --git a/test/ops/timeout/async.ts b/test/ops/timeout/async.ts
index 2f50268a..5e51eb80 100644
--- a/test/ops/timeout/async.ts
+++ b/test/ops/timeout/async.ts
@@ -1,29 +1,36 @@
 import {_asyncValues, expect} from '../../header';
-import {pipeAsync, delay, timeout, tap} from '../../../src';
+import {
+    pipeAsync,
+    delay,
+    timeout,
+    tap,
+    IterationState,
+    Operation
+} from '../../../src';
 
 export default () => {
     it('must end iteration after timeout', async () => {
-        const i = pipeAsync([1, 2, 3], delay(10), timeout(35));
+        const i = pipeAsync([1, 2, 3], interval(10), timeout(19));
         expect(await _asyncValues(i)).to.eql([1, 2]);
     });
     it('must emit nothing when timeout does not permit', async () => {
         let count: any;
         const i = pipeAsync(
-            [1, 2, 3],
-            delay(10),
-            timeout(1, (c) => {
+            [11, 22, 33],
+            interval(10),
+            timeout(3, (c) => {
                 count = c;
             })
         );
-        expect(await _asyncValues(i)).to.eql([]);
-        expect(count).to.eql(0);
+        expect(await _asyncValues(i)).to.eql([11]);
+        expect(count).to.eql(1);
     });
     it('must invoke callback on timeout', async () => {
         let count;
         const i = pipeAsync(
             [1, 2, 3],
-            delay(10),
-            timeout(29, (c) => {
+            interval(10),
+            timeout(19, (c) => {
                 count = c;
             })
         );
@@ -49,7 +56,7 @@ export default () => {
         let e: any;
         const i = pipeAsync(
             [1, 2, 3],
-            delay(10),
+            interval(10),
             timeout(1, () => {
                 throw new Error('timeout');
             })
@@ -80,3 +87,18 @@ export default () => {
         expect(count).to.be.undefined;
     });
 };
+
+/**
+ * Helper borrowed from iter-ops-extras, to avoid delaying first value in tests;
+ * https://github.com/vitaly-t/iter-ops-extras/blob/main/src/interval.ts
+ */
+function interval<T>(
+    timeout:
+        | number
+        | ((value: T, index: number, state: IterationState) => number)
+): Operation<T, T> {
+    if (typeof timeout === 'function') {
+        return delay((v, i, s) => (i ? timeout(v, i, s) : -1));
+    }
+    return delay((_, i) => (i ? timeout : -1));
+}