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src/functions/rate/index.ts

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+import { Transform } from "stream";
+import { performance } from "perf_hooks";
+import { sleep } from "../../helpers";
+import { TransformOptions } from "../definitions";
+/**
+ * Limits date of data transferred into stream.
+ * @param targetRate Desired rate in ms
+ * @param period Period to sleep for when rate is above or equal to targetRate
+ */
+export function rate(
+    targetRate: number = 50,
+    period: number = 2,
+    options: TransformOptions = {
+        readableObjectMode: true,
+        writableObjectMode: true,
+    },
+) {
+    const deltaMS = ((1 / targetRate) * 1000) / period; // Skip half a period
+    let total = 0;
+    const start = performance.now();
+    return new Transform({
+        async transform(data, encoding, callback) {
+            const currentRate = (total / (performance.now() - start)) * 1000;
+            if (targetRate && currentRate > targetRate) {
+                await sleep(deltaMS);
+            }
+            total += 1;
+            callback(undefined, data);
+        },
+    });
+}