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src/functions/concat/index.ts

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+import { Readable } from "stream";
+/**
+ * Return a Readable stream of readable streams concatenated together
+ * @param streams Readable streams to concatenate
+ */
+export function concat(...streams: Readable[]): Readable {
+    let isStarted = false;
+    let currentStreamIndex = 0;
+    const startCurrentStream = () => {
+        if (currentStreamIndex >= streams.length) {
+            wrapper.push(null);
+        } else {
+            streams[currentStreamIndex]
+                .on("data", chunk => {
+                    if (!wrapper.push(chunk)) {
+                        streams[currentStreamIndex].pause();
+                    }
+                })
+                .on("error", err => wrapper.emit("error", err))
+                .on("end", () => {
+                    currentStreamIndex++;
+                    startCurrentStream();
+                });
+        }
+    };
+
+    const wrapper = new Readable({
+        objectMode: true,
+        read() {
+            if (!isStarted) {
+                isStarted = true;
+                startCurrentStream();
+            }
+            if (currentStreamIndex < streams.length) {
+                streams[currentStreamIndex].resume();
+            }
+        },
+    });
+    return wrapper;
+}