Basic QR tests (+ number encoding fix) (#168)

* Basic QR tests (+ number encoding fix)

* skipEncoding for Address display

* Fixup comments

packages/react-qr/src/util.ts

@@ -2,8 +2,15 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
+import { u8aConcat, u8aToU8a } from '@polkadot/util';
+import { decodeAddress } from '@polkadot/util-crypto';
+
+import { ADDRESS_PREFIX, CMD_SIGN_TX, CRYPTO_SR25519, DEFAULT_IMG_SIZE, FRAME_SIZE, SUBSTRATE_ID } from './constants';
+
+const MULTIPART = new Uint8Array([0]);
+
 export function encodeNumber (value: number): Uint8Array {
-  return new Uint8Array([value >> 8, value & 256]);
+  return new Uint8Array([value >> 8, value & 0xff]);
 }
 
 export function encodeString (value: string): Uint8Array {
@@ -21,3 +28,49 @@ export function decodeString (value: Uint8Array): string {
     return str + String.fromCharCode(code);
   }, '');
 }
+
+export function createAddressPayload (address: string): Uint8Array {
+  return u8aConcat(
+    encodeString(ADDRESS_PREFIX),
+    encodeString(address)
+  );
+}
+
+export function createSignPayload (address: string, payload: string | Uint8Array): Uint8Array {
+  return u8aConcat(
+    SUBSTRATE_ID,
+    CRYPTO_SR25519,
+    CMD_SIGN_TX,
+    decodeAddress(address),
+    u8aToU8a(payload)
+  );
+}
+
+export function createFrames (input: Uint8Array): string[] {
+  const frames = [];
+  let idx = 0;
+
+  while (idx < input.length) {
+    frames.push(input.subarray(idx, idx + FRAME_SIZE));
+
+    idx += FRAME_SIZE;
+  }
+
+  return frames.map((frame, index: number): string =>
+    decodeString(u8aConcat(
+      MULTIPART,
+      encodeNumber(frames.length),
+      encodeNumber(index),
+      frame
+    ))
+  );
+}
+
+export function createImgSize (size: number = DEFAULT_IMG_SIZE): Record<string, string> {
+  const height = `${size}px`;
+
+  return {
+    height,
+    width: height
+  };
+}