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src/functions/baseFunctions.ts

@@ -19,4 +19,4 @@ export { replace } from "./replace";
 export { split } from "./split";
 export { stringify } from "./stringify";
 export { unbatch } from "./unbatch";
-export { compose } from "./compose";
+export { compose, composeDuplex } from "./compose";

src/functions/compose.ts

@@ -1,45 +1,54 @@
-import { Transform, Writable, Pipe, WritableOptions } from "stream";
-
-class Compose extends Writable implements Pipe {
-    private head: Writable | Transform;
-    private tail: Writable | Transform;
-    constructor(
-        streams: Array<Transform | Writable>,
-        options?: WritableOptions,
-    ) {
-        super(options);
-        if (streams.length < 2) {
-            throw new Error("Cannot compose 1 or less streams");
-        }
-        this.head = streams[0];
-        for (let i = 1; i < streams.length; i++) {
-            streams[i - 1].pipe(streams[i]);
-        }
-        this.tail = streams[streams.length - 1];
-    }
-
-    public pipe<T extends NodeJS.WritableStream>(
-        destination: T,
-        options: { end?: boolean } | undefined,
-    ) {
-        return this.tail.pipe(
-            destination,
-            options,
-        );
-    }
-
-    public _write(chunk: any, enc: string, cb: any) {
-        this.head.write(chunk.toString ? chunk.toString() : chunk, cb);
-    }
-}
+import {
+    pipeline,
+    Transform,
+    Writable,
+    Pipe,
+    WritableOptions,
+    Readable,
+    Duplex,
+} from "stream";
 
 /**
  * Return a Readable stream of readable streams concatenated together
  * @param streams Readable streams to concatenate
  */
+
+// First Readable --> Readable
+// First Transform | Duplex, Last Writable --> Writable
+//
 export function compose(
-    streams: Array<Transform | Writable>,
+    streams: Array<Readable | Duplex | Transform | Writable>,
     options?: WritableOptions,
-): Compose {
-    return new Compose(streams, options);
+): Duplex {
+    // Maybe just return a new stream here
+    if (streams.length < 2) {
+        throw new Error("Not enough");
+    }
+
+    const duplex = new Duplex({
+        objectMode: true,
+        write(chunk, enc, cb) {
+            const first = streams[0] as Writable;
+            if (!first.write(chunk)) {
+                first.on("drain", cb);
+            } else {
+                cb();
+            }
+        },
+        read(size) {
+            let chunk;
+            while (
+                null !==
+                (chunk = (streams[streams.length - 1] as Readable).read())
+            ) {
+                this.push(chunk);
+            }
+        },
+    });
+
+    pipeline(streams, (err: any) => {
+        duplex.emit("error", err);
+    });
+
+    return duplex;
 }

src/functions/index.ts

@@ -297,3 +297,9 @@ export function compose(
         options,
     );
 }
+export function composeDuplex(
+    streams: Array<Writable | Transform>,
+    options?: WritableOptions,
+) {
+    return baseFunctions.composeDuplex(streams, options);
+}

src/index.ts

@@ -22,4 +22,5 @@ export {
     accumulator,
     accumulatorBy,
     compose,
+    composeDuplex,
 } from "./functions";

tests/compose.spec.ts

@@ -1,20 +1,54 @@
 const test = require("ava");
-const { compose, map } = require("../src");
+const { compose, composeDuplex, map } = require("../src");
 
 test.cb("compose()", t => {
-    const first = map((chunk: number) => chunk * 2);
-    const second = map((chunk: number) => chunk + 1);
+    const first = map((chunk: number) => chunk + "x");
+    const second = map((chunk: number) => chunk + "y");
 
     const composed = compose(
         [first, second],
         { objectMode: true },
     );
+    const third = map((chunk: number) => chunk + "z");
+    composed
+        .pipe(third)
+        .on("data", data => console.log("Piped composed: ", data));
+
+    composed.on("data", data => {
+        console.log("data on composed", data);
+        t.end();
+    });
+    composed.on("error", data => {
+        console.log("ERROR", data);
+    });
+    composed.on("end", data => {
+        console.log("end", data);
+    });
 
     composed.write(1);
     composed.write(2);
-    composed.write(3);
+});
+test.cb.only("composeDuplex()", t => {
+    const first = map((chunk: number) => chunk + "x");
+    const second = map((chunk: number) => chunk + "y");
+
+    const composed = composeDuplex([first, second], { objectMode: true });
+    const third = map((chunk: number) => chunk + "z");
+    // composed
+    // .pipe(third)
+    // .on("data", data => console.log("Piped composed: ", data));
 
     composed.on("data", data => {
-        console.log("DATA", data);
+        console.log("data on composed", data);
+        t.end();
     });
+    composed.on("error", data => {
+        console.log("ERROR", data);
+    });
+    composed.on("end", data => {
+        console.log("end", data);
+    });
+
+    composed.write(1);
+    composed.write(2);
 });