Added simple Key-Value store to support temporary data

ReactNativeClient/lib/services/KvStore.js

@@ -0,0 +1,80 @@
+const BaseService = require('lib/services/BaseService.js');
+const Mutex = require('async-mutex').Mutex;
+
+class KvStore extends BaseService {
+
+	static instance() {
+		if (this.instance_) return this.instance_;
+		this.instance_ = new KvStore();
+		return this.instance_;
+	}
+
+	constructor() {
+		super();
+		this.incMutex_ = new Mutex();
+	}
+
+	setDb(v) {
+		this.db_ = v;
+	}
+
+	db() {
+		if (!this.db_) throw new Error('Accessing DB before it has been set!');
+		return this.db_;
+	}
+
+	typeFromValue_(value) {
+		if (typeof value === 'string') return KvStore.TYPE_TEXT;
+		if (typeof value === 'number') return KvStore.TYPE_INT;
+		throw new Error('Unsupported value type: ' + (typeof value));
+	}
+
+	formatValue_(value, type) {
+		if (type === KvStore.TYPE_INT) return Number(value);
+		if (type === KvStore.TYPE_TEXT) return value + '';
+		throw new Error('Unknown type: ' + type);
+	}
+
+	async value(key) {
+		const r = await this.db().selectOne('SELECT `value`, `type` FROM key_values WHERE `key` = ?', [key]);
+		if (!r) return null;
+		return this.formatValue_(r.value, r.type);
+	}
+
+	async setValue(key, value) {
+		const t = Date.now();
+		await this.db().exec('INSERT OR REPLACE INTO key_values (`key`, `value`, `type`, `updated_time`) VALUES (?, ?, ?, ?)', [key, value, this.typeFromValue_(value), t]);
+	}
+
+	async deleteValue(key) {
+		await this.db().exec('DELETE FROM key_values WHERE `key` = ?', [key]);
+	}
+
+	// Note: atomicity is done at application level so two difference instances
+	// accessing the db at the same time could mess up the increment.
+	async incValue(key, inc = 1) {
+		const release = await this.incMutex_.acquire();
+
+		try {
+			const result = await this.db().selectOne('SELECT `value`, `type` FROM key_values WHERE `key` = ?', [key]);
+			const newValue = result ? this.formatValue_(result.value, result.type) + inc : inc;
+			await this.setValue(key, newValue);
+			release();
+			return newValue;
+		} catch (error) {
+			release();
+			throw error;
+		}		
+	}
+
+	async countKeys() {
+		const r = await this.db().selectOne('SELECT count(*) as total FROM key_values');
+		return r.total ? r.total : 0;
+	}
+
+}
+
+KvStore.TYPE_INT = 1;
+KvStore.TYPE_TEXT = 2;
+
+module.exports = KvStore;