Update code for the review comments

* Make decode module return value `ImageData`
* Fix global definition of ImageData
* Use concrete Encoder types for encode functions
* Use ArrayBufferView in FileLike instead of using a similar type
* Throw error when the `encode` functions
return null
* Use generic types for WorkerPool
* Fix `encode` function typing
in `index.ts`
* Remove ts-ignore for web-streams-polyfill
and handle nulls for TransformStream
* Fix rollup entry point (now we need to have
`index.ts` instead of `index.js`)

libsquoosh/src/worker_pool.ts

@@ -1,7 +1,5 @@
 import { Worker, parentPort } from 'worker_threads';
-// @ts-ignore
 import { TransformStream } from 'web-streams-polyfill';
-import type { JobMessage } from './index';
 
 function uuid() {
   return Array.from({ length: 16 }, () =>
@@ -9,28 +7,16 @@ function uuid() {
   ).join('');
 }
 
-function jobPromise(worker: Worker, msg: JobMessage) {
-  return new Promise((resolve, reject) => {
-    const id = uuid();
-    worker.postMessage({ msg, id });
-    worker.on('message', function f({ error, result, id: rid }) {
-      if (rid !== id) {
-        return;
-      }
-      if (error) {
-        reject(error);
-        return;
-      }
-      worker.off('message', f);
-      resolve(result);
-    });
-  });
+interface Job<I> {
+  msg: I;
+  resolve: Function;
+  reject: Function;
 }
 
-export default class WorkerPool {
+export default class WorkerPool<I, O> {
   public numWorkers: number;
-  public jobQueue: TransformStream;
-  public workerQueue: TransformStream;
+  public jobQueue: TransformStream<Job<I>, Job<I>>;
+  public workerQueue: TransformStream<Worker, Worker>;
   public done: Promise<void>;
 
   constructor(numWorkers: number, workerFile: string) {
@@ -55,9 +41,14 @@ export default class WorkerPool {
         await this._terminateAll();
         return;
       }
+
+      if (!value) {
+        throw new Error('Reader did not return any value');
+      }
+
       const { msg, resolve, reject } = value;
       const worker = await this._nextWorker();
-      jobPromise(worker, msg)
+      this.jobPromise(worker, msg)
         .then((result) => resolve(result))
         .catch((reason) => reject(reason))
         .finally(() => {
@@ -73,6 +64,10 @@ export default class WorkerPool {
     const reader = this.workerQueue.readable.getReader();
     const { value } = await reader.read();
     reader.releaseLock();
+    if (!value) {
+      throw new Error('No worker left');
+    }
+
     return value;
   }
 
@@ -89,7 +84,7 @@ export default class WorkerPool {
     await this.done;
   }
 
-  dispatchJob(msg: JobMessage): Promise<any> {
+  dispatchJob(msg: I): Promise<O> {
     return new Promise((resolve, reject) => {
       const writer = this.jobQueue.writable.getWriter();
       writer.write({ msg, resolve, reject });
@@ -97,7 +92,25 @@ export default class WorkerPool {
     });
   }
 
-  static useThisThreadAsWorker(cb: (msg: JobMessage) => any) {
+  private jobPromise(worker: Worker, msg: I) {
+    return new Promise((resolve, reject) => {
+      const id = uuid();
+      worker.postMessage({ msg, id });
+      worker.on('message', function f({ error, result, id: rid }) {
+        if (rid !== id) {
+          return;
+        }
+        if (error) {
+          reject(error);
+          return;
+        }
+        worker.off('message', f);
+        resolve(result);
+      });
+    });
+  }
+
+  static useThisThreadAsWorker<I, O>(cb: (msg: I) => O) {
     parentPort!.on('message', async (data) => {
       const { msg, id } = data;
       try {