Derive primaryFormat with a dedicated getPrimaryFormat utility

This implements a single algorithm responsible for getting a wallet's
primaryFormat.
This function uses the existing algorithm for publicKeys and is
now also used in `createPrivateKey`.
This change should be an idempotent, but guarantees our future changes
(about how we select the primary key) is couple to the appropriate
routines.
The goal is to future-proof our existing implementation for when we
enable new wallet formats.

We do not introduce any side-effects to existing wallets (wallets
already persisted prior to any change).

Author: samholmes

src/common/plugin/makeCurrencyTools.ts

@@ -16,6 +16,7 @@ import { parsePathname } from '../utxobased/engine/utils'
 import {
   asNumbWalletInfo,
   asPrivateKey,
+  getPrimaryFormat,
   PrivateKey
 } from '../utxobased/keymanager/cleaners'
 import { EncodeUriMetadata, ExtendedParseUri, PluginInfo } from './types'
@@ -42,10 +43,11 @@ export function makeCurrencyTools(
       opts?: JsonObject
     ): Promise<JsonObject> {
       const mnemonic = bip39.entropyToMnemonic(Buffer.from(io.random(32)))
+      const currencyFormats = engineInfo.formats ?? (['bip44'] as ['bip44'])
 
       const privateKey: PrivateKey = {
         seed: mnemonic,
-        format: opts?.format ?? engineInfo.formats?.[0] ?? 'bip44',
+        format: getPrimaryFormat(currencyFormats, currencyFormats),
         coinType: opts?.coinType ?? coinInfo.coinType ?? 0
       }
 

src/common/utxobased/keymanager/cleaners.ts

@@ -99,6 +99,31 @@ export const getSupportedFormats = (
   }
 }
 
+/**
+ * An algorithm that defines the primary format for a wallet given all of the
+ * wallet's formats and the currency formats (from plugin info).
+ *
+ * The purpose for this algorithm is to deterministically return a single
+ * primary format regardless of the order of the wallet formats given.
+ * The algorithm effectively takes the first format in the formats from plugin
+ * info that matches one of the formats in the given wallet formats.
+ *
+ * If no wallet format matches any of the formats in the plugin info, then
+ * the primary format is the first format in the wallet format after sorting
+ * in ascending order lexicographically.
+ */
+export const getPrimaryFormat = (
+  currencyFormats: CurrencyFormat[],
+  walletFormats: CurrencyFormat[]
+): CurrencyFormat => {
+  return (
+    (currencyFormats.length > 0
+      ? currencyFormats.find(format => walletFormats.includes(format))
+      : undefined) ??
+    walletFormats.sort((a, b) => (a === b ? 0 : a > b ? 1 : -1))[0]
+  )
+}
+
 /**
  * A cleaner that desensitizes the walletInfo object, excluding sensitive
  * keys (seed/mnemonic, sync key, data key, etc). By using this object type
@@ -147,16 +172,10 @@ export const asNumbWalletInfo = (
       if (walletFormats.length === 0) {
         throw new Error('Missing wallet public keys')
       }
-
-      // Search the engineInfo's formats array for the first format that exists
-      // in the publicKey data.
-      // If there are no defined formats in the engineInfo, then fallback to the
-      // first format in the publicKey after sorting alphabetically.
-      const primaryFormat =
-        (engineInfo.formats != null && engineInfo.formats.length > 0
-          ? engineInfo.formats.find(format => walletFormats.includes(format))
-          : undefined) ??
-        walletFormats.sort((a, b) => (a === b ? 0 : a > b ? 1 : -1))[0]
+      const primaryFormat = getPrimaryFormat(
+        engineInfo.formats ?? [],
+        walletFormats
+      )
 
       return {
         id,
@@ -181,6 +200,8 @@ export const asNumbWalletInfo = (
         id,
         type,
         keys: {
+          // Private key format is the primary format because it was determined
+          // during `createPrivateKey` phase.
           primaryFormat: privateKey.format,
           walletFormats,
           publicKey: { publicKeys: publicKey }