Revert "fix(js): use pure JS SHA256 library, refactor (#471)" (#475)

This reverts commit 7b84904d15.

web/js/proof-of-work-slow.mjs

@@ -0,0 +1,90 @@
+// https://dev.to/ratmd/simple-proof-of-work-in-javascript-3kgm
+
+export default function process(
+  data,
+  difficulty = 5,
+  signal = null,
+  progressCallback = null,
+  _threads = 1,
+) {
+  console.debug("slow algo");
+  return new Promise((resolve, reject) => {
+    let webWorkerURL = URL.createObjectURL(new Blob([
+      '(', processTask(), ')()'
+    ], { type: 'application/javascript' }));
+
+    let worker = new Worker(webWorkerURL);
+    const terminate = () => {
+      worker.terminate();
+      if (signal != null) {
+        // clean up listener to avoid memory leak
+        signal.removeEventListener("abort", terminate);
+        if (signal.aborted) {
+          console.log("PoW aborted");
+          reject(false);
+        }
+      }
+    };
+    if (signal != null) {
+      signal.addEventListener("abort", terminate, { once: true });
+    }
+
+    worker.onmessage = (event) => {
+      if (typeof event.data === "number") {
+        progressCallback?.(event.data);
+      } else {
+        terminate();
+        resolve(event.data);
+      }
+    };
+
+    worker.onerror = (event) => {
+      terminate();
+      reject(event);
+    };
+
+    worker.postMessage({
+      data,
+      difficulty
+    });
+
+    URL.revokeObjectURL(webWorkerURL);
+  });
+}
+
+function processTask() {
+  return function () {
+    const sha256 = (text) => {
+      const encoded = new TextEncoder().encode(text);
+      return crypto.subtle.digest("SHA-256", encoded.buffer)
+        .then((result) =>
+          Array.from(new Uint8Array(result))
+            .map((c) => c.toString(16).padStart(2, "0"))
+            .join(""),
+        );
+    };
+
+    addEventListener('message', async (event) => {
+      let data = event.data.data;
+      let difficulty = event.data.difficulty;
+
+      let hash;
+      let nonce = 0;
+      do {
+        if (nonce & 1023 === 0) {
+          postMessage(nonce);
+        }
+        hash = await sha256(data + nonce++);
+      } while (hash.substring(0, difficulty) !== Array(difficulty + 1).join('0'));
+
+      nonce -= 1; // last nonce was post-incremented
+
+      postMessage({
+        hash,
+        data,
+        difficulty,
+        nonce,
+      });
+    });
+  }.toString();
+}