feat(Implement functionality for a complete USSD request):

Adds in-cache session management handler as plugin.

src/plugins/handler/ussdSession.ts

@@ -0,0 +1,60 @@
+import Redis from 'ioredis';
+import {
+  JsonObject,
+  JsonProperty,
+  JsonSerializer
+} from 'typescript-json-serializer';
+
+import {
+  CacheAccessor
+} from "@utils/helpers/redis";
+
+
+type SessionData = Record<string, string | number> ;
+
+interface UssdSessionObject {
+  actorInput: string;
+  data: SessionData;
+  lastState: string;
+  ussdCode: string;
+  version: number;
+}
+
+@JsonObject()
+export class UssdSession extends CacheAccessor {
+  actorInput: string;
+  @JsonProperty()
+  data: SessionData;
+  @JsonProperty()
+  lastState: string;
+  @JsonProperty()
+  ussdCode: string;
+  @JsonProperty()
+  version: number;
+
+  constructor(cacheClient: Redis, cacheKey: string, serializer: JsonSerializer, UssdSessionObject: UssdSessionObject) {
+    super(cacheClient, cacheKey, serializer);
+    this.actorInput = UssdSessionObject.actorInput;
+    this.data = UssdSessionObject.data;
+    this.lastState = UssdSessionObject.lastState;
+    this.ussdCode = UssdSessionObject.ussdCode;
+    this.version = UssdSessionObject.version;
+  }
+
+  async create(serializer: JsonSerializer, ussdSession: UssdSession, expiration = 180) {
+    await this.cacheJSONData(serializer.serialize(ussdSession), expiration);
+  }
+
+  async get(cache: Redis, cacheKey: string, serializer: JsonSerializer) {
+    const serializedSession = await this.getCacheJSONData();
+    if (serializedSession) {
+      return serializer.deserialize(serializedSession, UssdSession);
+    } else {
+      return serializedSession;
+    }
+  }
+
+  async update(cache: Redis, cacheKey: string, serializer: JsonSerializer, ussdSession: UssdSession) {
+    await this.cacheJSONData(serializer.serialize(ussdSession));
+  }
+}