feat: Improve KV data caching and deserialization (#903)

**Requirements**

- [X] I have added test coverage for new or changed functionality
- [X] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [X] I have validated my changes against all supported platform
versions

**Describe the solution you've provided**
Improve KV data caching and deserialization

Author: abarker-launchdarkly

packages/sdk/fastly/src/api/EdgeFeatureStore.ts

@@ -14,7 +14,7 @@ export interface EdgeProvider {
 
 export class EdgeFeatureStore implements LDFeatureStore {
   private readonly _rootKey: string;
-  private _kvData: string | null = null;
+  private _deserializedPromise: Promise<LDFeatureStoreDataStorage | null> | null = null;
 
   constructor(
     private readonly _edgeProvider: EdgeProvider,
@@ -30,11 +30,36 @@ export class EdgeFeatureStore implements LDFeatureStore {
    * has a limit of 32 backend requests (including requests to fetch the KV data).
    * https://docs.fastly.com/products/compute-resource-limits
    */
-  private async _getKVData(): Promise<string | null | undefined> {
-    if (!this._kvData) {
-      this._kvData = await this._edgeProvider.get(this._rootKey);
+  private async _getKVData(): Promise<LDFeatureStoreDataStorage | null> {
+    if (!this._deserializedPromise) {
+      this._deserializedPromise = (async (): Promise<LDFeatureStoreDataStorage | null> => {
+        this._logger.debug('No cached data found, loading from KV store');
+        const kvData = await this._edgeProvider.get(this._rootKey);
+        if (!kvData) {
+          this._logger.debug('No data found in KV store');
+          return null;
+        }
+
+        this._logger.debug('Deserializing KV store data');
+        const deserialized = deserializePoll(kvData);
+        if (!deserialized) {
+          this._logger.debug('Failed to deserialize KV store data');
+          return null;
+        }
+
+        // Convert FlagsAndSegments to LDFeatureStoreDataStorage format
+        const deserializedData: LDFeatureStoreDataStorage = {
+          features: deserialized.flags,
+          segments: deserialized.segments,
+        };
+        this._logger.debug('Successfully cached deserialized data');
+
+        return deserializedData;
+      })();
+    } else {
+      this._logger.debug('Using cached deserialized data');
     }
-    return this._kvData;
+    return this._deserializedPromise;
   }
 
   async get(
@@ -47,23 +72,18 @@ export class EdgeFeatureStore implements LDFeatureStore {
     this._logger.debug(`Requesting ${dataKey} from ${this._rootKey}.${kindKey}`);
 
     try {
-      const i = await this._getKVData();
+      const data = await this._getKVData();
 
-      if (!i) {
+      if (!data) {
         throw new Error(`${this._rootKey}.${kindKey} is not found in KV.`);
       }
 
-      const item = deserializePoll(i);
-      if (!item) {
-        throw new Error(`Error deserializing ${kindKey}`);
-      }
-
       switch (namespace) {
         case 'features':
-          callback(item.flags[dataKey]);
+          callback(data.features[dataKey]);
           break;
         case 'segments':
-          callback(item.segments[dataKey]);
+          callback(data.segments[dataKey]);
           break;
         default:
           callback(null);
@@ -79,22 +99,17 @@ export class EdgeFeatureStore implements LDFeatureStore {
     const kindKey = namespace === 'features' ? 'flags' : namespace;
     this._logger.debug(`Requesting all from ${this._rootKey}.${kindKey}`);
     try {
-      const i = await this._getKVData();
-      if (!i) {
+      const data = await this._getKVData();
+      if (!data) {
         throw new Error(`${this._rootKey}.${kindKey} is not found in KV.`);
       }
 
-      const item = deserializePoll(i);
-      if (!item) {
-        throw new Error(`Error deserializing ${kindKey}`);
-      }
-
       switch (namespace) {
         case 'features':
-          callback(item.flags);
+          callback(data.features);
           break;
         case 'segments':
-          callback(item.segments);
+          callback(data.segments);
           break;
         default:
           callback({});
@@ -106,13 +121,22 @@ export class EdgeFeatureStore implements LDFeatureStore {
   }
 
   async initialized(callback: (isInitialized: boolean) => void = noop): Promise<void> {
-    const config = await this._getKVData();
-    const result = config !== null;
-    this._logger.debug(`Is ${this._rootKey} initialized? ${result}`);
-    callback(result);
+    try {
+      const deserialized = await this._getKVData();
+      const result = deserialized !== null;
+      this._logger.debug(`Is ${this._rootKey} initialized? ${result}`);
+      callback(result);
+    } catch (err) {
+      this._logger.error(err);
+      this._logger.debug(`Is ${this._rootKey} initialized? false`);
+      callback(false);
+    }
   }
 
   init(allData: LDFeatureStoreDataStorage, callback: () => void): void {
+    this._getKVData().catch((err) => {
+      this._logger.error(err);
+    });
     callback();
   }