feat: add basic impl

pkgs/solver/src/lib.ts

@@ -1,3 +1,56 @@
-export function solve(): void {
+export async function solveJs(
+	nonce: Uint8Array,
+	target: Uint8Array,
+): Promise<Uint8Array> {
+	const arr = new Uint8Array(8 + nonce.byteLength);
+	const solutionView = new DataView(arr.buffer, 0, 8);
+	arr.set(nonce, 8);
 
+	for (
+		let i = BigInt(0);
+		// eslint-disable-next-line no-constant-condition
+		true;
+		i++
+	) {
+		solutionView.setBigUint64(0, i, true);
+
+		const hashArrayBuf = await crypto.subtle.digest("SHA-256", arr);
+		const hash = new Uint8Array(hashArrayBuf);
+
+		if (arrayStartsWith(hash, target)) {
+			return new Uint8Array(
+				solutionView.buffer,
+				solutionView.byteOffset,
+				solutionView.byteLength,
+			);
+		}
+	}
+}
+
+export async function verify(
+	nonce: Uint8Array,
+	target: Uint8Array,
+	solution: Uint8Array,
+): Promise<boolean> {
+	const arr = new Uint8Array(solution.byteLength + nonce.byteLength);
+	arr.set(solution);
+	arr.set(nonce, solution.byteLength);
+
+	const hashArrayBuf = await crypto.subtle.digest("SHA-256", arr);
+	const hash = new Uint8Array(hashArrayBuf);
+
+	return arrayStartsWith(hash, target);
+}
+
+function arrayStartsWith(array: Uint8Array, search: Uint8Array): boolean {
+	const searchLen = search.length;
+	if (searchLen > array.length) {
+		return false;
+	}
+	for (let i = 0; i < searchLen; i += 1) {
+		if (array[i] !== search[i]) {
+			return false;
+		}
+	}
+	return true;
 }