COVIDSafe code from version 2.0 (#37)

CovidSafe/Herald/Sensor/Data/BatteryLog.swift

@@ -0,0 +1,50 @@
+//
+//  BatteryLog.swift
+//
+//  Copyright 2020 VMware, Inc.
+//  SPDX-License-Identifier: MIT
+//
+
+import UIKit
+import NotificationCenter
+import os
+
+/// Battery log for monitoring battery level over time
+class BatteryLog {
+    private let logger = ConcreteSensorLogger(subsystem: "Sensor", category: "BatteryLog")
+    private let textFile: TextFile
+    private let dateFormatter = DateFormatter()
+    private let updateInterval = TimeInterval(30)
+
+    init(filename: String) {
+        textFile = TextFile(filename: filename)
+        if textFile.empty() {
+            textFile.write("time,source,level")
+        }
+        dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
+        UIDevice.current.isBatteryMonitoringEnabled = true
+        NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelDidChange), name: UIDevice.batteryLevelDidChangeNotification, object: nil)
+        NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: UIDevice.batteryStateDidChangeNotification, object: nil)
+        let _ = Timer.scheduledTimer(timeInterval: updateInterval, target: self, selector: #selector(update), userInfo: nil, repeats: true)
+    }
+    
+    private func timestamp() -> String {
+        let timestamp = dateFormatter.string(from: Date())
+        return timestamp
+    }
+
+    @objc func update() {
+        let powerSource = (UIDevice.current.batteryState == .unplugged ? "battery" : "external")
+        let batteryLevel = Float(UIDevice.current.batteryLevel * 100).description
+        textFile.write(timestamp() + "," + powerSource + "," + batteryLevel)
+        logger.debug("update (powerSource=\(powerSource),batteryLevel=\(batteryLevel))");
+    }
+    
+    @objc func batteryLevelDidChange(_ sender: NotificationCenter) {
+        update()
+    }
+    
+    @objc func batteryStateDidChange(_ sender: NotificationCenter) {
+        update()
+    }
+}