Removed cache package dependency and implemented one more suitable for React Native

ReactNativeClient/lib/InMemoryCache.ts

@@ -0,0 +1,84 @@
+// There are plenty of packages for in-memory caching but each have their
+// own gotchas and often have extra complexity which makes it work in one
+// platform but not in another (for example, the use of long timeouts would
+// be fine in Node but not in React Native).
+//
+// So this class implements a simple in-memory cache with support for TTL.
+// Checking for expired keys is a bit inefficient since it doesn't rely on
+// timers, so it's checking every time a value is set or retrieved. But it
+// should be fine in most cases, as long as the class is not used at a massive
+// scale.
+
+interface Record {
+	value: any,
+	expiredTime: number,
+}
+
+interface Records {
+	[key:string]: Record;
+}
+
+interface ExpirableKeys {
+	[key:string]: boolean,
+}
+
+export default class Cache {
+
+	private maxRecords_:number;
+	private records_:Records = {};
+	private expirableKeys_:ExpirableKeys = {};
+	private recordKeyHistory_:string[] = [];
+
+	constructor(maxRecords:number = 50) {
+		this.maxRecords_ = maxRecords;
+	}
+
+	private checkExpiredRecords() {
+		const now = Date.now();
+
+		for (let key in this.expirableKeys_) {				
+			if (!this.records_[key]) {
+				delete this.expirableKeys_[key];
+			} else {
+				if (this.records_[key].expiredTime <= now) {
+					delete this.records_[key];
+					delete this.expirableKeys_[key];
+				}
+			}
+		}
+
+		while (this.recordKeyHistory_.length > this.maxRecords_) {
+			const key = this.recordKeyHistory_[0];
+			delete this.records_[key];
+			delete this.expirableKeys_[key];
+			this.recordKeyHistory_.splice(0, 1);
+		}
+	}
+
+	public value(key:string, defaultValue:any = undefined):any {
+		this.checkExpiredRecords();
+		if (key in this.records_) return this.records_[key].value;
+
+		return defaultValue;
+	}
+
+	public setValue(key:string, value:any, ttl:number = 0) {
+		this.checkExpiredRecords();
+
+		this.records_[key] = {
+			value: value,
+			expiredTime: ttl ? Date.now() + ttl : 0,
+		}
+
+		const idx = this.recordKeyHistory_.indexOf(key);
+		if (idx >= 0) this.recordKeyHistory_.splice(idx, 1);
+		this.recordKeyHistory_.push(key);
+
+		if (ttl) {
+			this.expirableKeys_[key] = true;
+		} else {
+			delete this.expirableKeys_[key];
+		}
+	}
+
+}