Add a versioned wallet UI-state cache file and Redux seeding action

Add walletCache.json (name, fiat code, enabled token IDs, last-known
balances) with a versioned cleaner, plus a CURRENCY_WALLET_CACHE_LOADED
action that seeds the wallet's Redux slice. Cached balances never
overwrite live engine data, and the later authoritative file loads
replace the cached values exactly as they replace initial state today.

Author: j0ntz

src/core/actions.ts

@@ -1,4 +1,5 @@
 import {
+  EdgeBalanceMap,
   EdgeCorePlugin,
   EdgeCorePluginsInit,
   EdgeCurrencyTools,
@@ -271,6 +272,18 @@ export type RootAction =
         tools: Promise<EdgeCurrencyTools>
       }
     }
+  | {
+      // Called when the wallet's UI-state cache file loads from disk,
+      // seeding Redux before the engine exists.
+      type: 'CURRENCY_WALLET_CACHE_LOADED'
+      payload: {
+        balanceMap: EdgeBalanceMap
+        enabledTokenIds: string[]
+        fiatCurrencyCode: string
+        name: string | null
+        walletId: string
+      }
+    }
   | {
       type: 'CURRENCY_WALLET_CHANGED_PAUSED'
       payload: {

src/core/currency/wallet/currency-wallet-cleaners.ts

@@ -402,6 +402,30 @@ export const asPublicKeyFile = asObject({
   })
 })
 
+/**
+ * Cached wallet UI state, stored in the wallet's local storage.
+ * This is everything the GUI needs to render a wallet in the wallet list
+ * before its engine exists. Balances are last-known values,
+ * and are explicitly allowed to be stale.
+ */
+export interface WalletCacheFile {
+  version: 1
+  name: string | null
+  fiatCurrencyCode: string
+  enabledTokenIds: string[]
+
+  /** Integer strings. The `null` tokenId is spelled '' here. */
+  balances: { [tokenId: string]: string }
+}
+
+export const asWalletCacheFile: Cleaner<WalletCacheFile> = asObject({
+  version: asValue(1),
+  name: asEither(asString, asNull),
+  fiatCurrencyCode: asString,
+  enabledTokenIds: asArray(asString),
+  balances: asObject(asIntegerString)
+})
+
 /**
  * The wallet's local storage file for the last seen "checkpoint". The core
  * does not know the contents of the checkpoint, so it just as an arbitrary

src/core/currency/wallet/currency-wallet-reducer.ts

@@ -197,6 +197,8 @@ const currencyWalletInner = buildReducer<
         return action.payload.enabledTokenIds
       } else if (action.type === 'CURRENCY_WALLET_ENABLED_TOKENS_CHANGED') {
         return action.payload.enabledTokenIds
+      } else if (action.type === 'CURRENCY_WALLET_CACHE_LOADED') {
+        return action.payload.enabledTokenIds
       } else if (action.type === 'CURRENCY_ENGINE_DETECTED_TOKENS') {
         const { enablingTokenIds } = action.payload
         return uniqueStrings([...state, ...enablingTokenIds])
@@ -282,13 +284,17 @@ const currencyWalletInner = buildReducer<
   },
 
   fiat(state = '', action): string {
-    return action.type === 'CURRENCY_WALLET_FIAT_CHANGED'
+    return action.type === 'CURRENCY_WALLET_FIAT_CHANGED' ||
+      action.type === 'CURRENCY_WALLET_CACHE_LOADED'
       ? action.payload.fiatCurrencyCode
       : state
   },
 
   fiatLoaded(state = false, action): boolean {
-    return action.type === 'CURRENCY_WALLET_FIAT_CHANGED' ? true : state
+    return action.type === 'CURRENCY_WALLET_FIAT_CHANGED' ||
+      action.type === 'CURRENCY_WALLET_CACHE_LOADED'
+      ? true
+      : state
   },
 
   files(state = {}, action): TxFileJsons {
@@ -352,6 +358,14 @@ const currencyWalletInner = buildReducer<
       out.set(tokenId, balance)
       return out
     }
+    if (action.type === 'CURRENCY_WALLET_CACHE_LOADED') {
+      // Seed cached balances, but never overwrite live engine data:
+      const out = new Map(state)
+      for (const [tokenId, balance] of action.payload.balanceMap) {
+        if (!out.has(tokenId)) out.set(tokenId, balance)
+      }
+      return out
+    }
     return state
   },
 
@@ -379,13 +393,17 @@ const currencyWalletInner = buildReducer<
   },
 
   name(state = null, action): string | null {
-    return action.type === 'CURRENCY_WALLET_NAME_CHANGED'
+    return action.type === 'CURRENCY_WALLET_NAME_CHANGED' ||
+      action.type === 'CURRENCY_WALLET_CACHE_LOADED'
       ? action.payload.name
       : state
   },
 
   nameLoaded(state = false, action): boolean {
-    return action.type === 'CURRENCY_WALLET_NAME_CHANGED' ? true : state
+    return action.type === 'CURRENCY_WALLET_NAME_CHANGED' ||
+      action.type === 'CURRENCY_WALLET_CACHE_LOADED'
+      ? true
+      : state
   },
 
   seenTxCheckpoint(state = null, action) {

src/core/currency/wallet/wallet-cache-file.ts

@@ -0,0 +1,17 @@
+import { makeJsonFile } from '../../../util/file-helpers'
+import { asWalletCacheFile } from './currency-wallet-cleaners'
+
+/**
+ * Cached wallet UI state, stored on the wallet's local disklet
+ * alongside `publicKey.json`. See `asWalletCacheFile` for the schema.
+ */
+export const WALLET_CACHE_FILE = 'walletCache.json'
+export const walletCacheFile = makeJsonFile(asWalletCacheFile)
+
+/**
+ * Tuning for the wallet UI-state cache saver.
+ * Tests override the throttle to run quickly.
+ */
+export const walletCacheSaverConfig = {
+  throttleMs: 5000
+}