Pebble: implement battery display in control center

- extract the millivolts reading from the analytics datalog message and map to percentage
- mapping is manually made and is possibly wrong, but the values are commented
- the values are sent once per hour and are delayed, this might make the reading really inaccurate on pebble time round watches

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/pebble/DatalogSessionAnalytics.java

@@ -0,0 +1,97 @@
+/*  Copyright (C) 2016-2017 Daniele Gobbetti
+
+    This file is part of Gadgetbridge.
+
+    Gadgetbridge is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Gadgetbridge is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
+package nodomain.freeyourgadget.gadgetbridge.service.devices.pebble;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.util.UUID;
+
+import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEvent;
+import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEventBatteryInfo;
+import nodomain.freeyourgadget.gadgetbridge.impl.GBDevice;
+import nodomain.freeyourgadget.gadgetbridge.model.BatteryState;
+import nodomain.freeyourgadget.gadgetbridge.util.GB;
+
+class DatalogSessionAnalytics extends DatalogSession {
+    private static final Logger LOG = LoggerFactory.getLogger(DatalogSessionAnalytics.class);
+    private GBDeviceEventBatteryInfo mGBDeviceEventBatteryInfo = new GBDeviceEventBatteryInfo();
+    private GBDevice mGBDevice;
+
+    DatalogSessionAnalytics(byte id, UUID uuid, int timestamp, int tag, byte itemType, short itemSize, GBDevice device) {
+        super(id, uuid, timestamp, tag, itemType, itemSize);
+        if (mGBDevice == null || !device.equals(mGBDevice)) { //prevent showing information of other pebble watches when switching devices
+            mGBDevice = device;
+            mGBDeviceEventBatteryInfo.state = BatteryState.UNKNOWN;
+        }
+
+        // The default notification should not be too bad (one per hour) but we can override this if needed
+        //mGBDevice.setBatteryThresholdPercent((short) 5);
+
+        taginfo = "(analytics - " + tag + ")";
+    }
+
+    @Override
+    GBDeviceEvent[] handleMessage(ByteBuffer datalogMessage, int length) {
+        LOG.info("DATALOG " + taginfo + GB.hexdump(datalogMessage.array(), datalogMessage.position(), length));
+
+        datalogMessage.position(datalogMessage.position() + 3);
+        int messageTS = datalogMessage.getInt();
+
+        datalogMessage.position(datalogMessage.position() + 12);
+        short reportedMilliVolts = datalogMessage.getShort();
+
+        LOG.info("Battery reading for TS " + messageTS + " is: " + reportedMilliVolts + " milliVolts, mapped to percentage: " + milliVoltstoPercentage(reportedMilliVolts));
+
+        if (messageTS > 0 && reportedMilliVolts < 5000) { //some safety checks
+            mGBDeviceEventBatteryInfo.state = BatteryState.BATTERY_NORMAL;
+            mGBDeviceEventBatteryInfo.level = milliVoltstoPercentage(reportedMilliVolts);
+
+            return new GBDeviceEvent[]{mGBDeviceEventBatteryInfo, null};
+        } else { //invalid data, but we ack nevertheless
+            return new GBDeviceEvent[]{null};
+        }
+
+    }
+
+    private short milliVoltstoPercentage(short batteryMilliVolts) {
+        if (batteryMilliVolts > 4145) {        //(4146 is still 100, next reported value is already 90)
+            return 100;
+        } else if (batteryMilliVolts > 4053) { //(4054 is still 90, next reported value is already 80)
+            return 90;
+        } else if (batteryMilliVolts > 4000) { //guessed
+            return 80;
+        } else if (batteryMilliVolts > 3880) { //confirmed
+            return 70;
+        } else if (batteryMilliVolts > 3855) { //probably
+            return 60;
+        } else if (batteryMilliVolts > 3780) { //3781 is still 50, next reading is 3776 but percentage on pebble unknown
+            return 50;
+        } else if (batteryMilliVolts >= 3750) { //3750 is still 40, next reported value is 3746 and already 30
+            return 40;
+        } else if (batteryMilliVolts > 3720) { //3723 is still 30, next reported value is 3719 and already 20
+            return 30;
+        } else if (batteryMilliVolts > 3680) { //3683 is still 20, next reported value is 3675 and already 10
+            return 20;
+        } else if (batteryMilliVolts > 3650) { //3657 is still 10
+            return 10;
+        } else {
+            return 0; //or -1 for invalid?
+        }
+    }
+}

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/pebble/PebbleProtocol.java

@@ -2263,7 +2263,9 @@ public class PebbleProtocol extends GBDeviceProtocol {
                 short item_size = buf.getShort();
                 LOG.info("DATALOG OPENSESSION. id=" + (id & 0xff) + ", App UUID=" + uuid.toString() + ", log_tag=" + log_tag + ", item_type=" + item_type + ", itemSize=" + item_size);
                 if (!mDatalogSessions.containsKey(id)) {
-                    if (uuid.equals(UUID_ZERO) && log_tag == 81) {
+                    if (uuid.equals(UUID_ZERO) && log_tag == 78) {
+                        mDatalogSessions.put(id, new DatalogSessionAnalytics(id, uuid, timestamp, log_tag, item_type, item_size, getDevice()));
+                    } else if (uuid.equals(UUID_ZERO) && log_tag == 81) {
                         mDatalogSessions.put(id, new DatalogSessionHealthSteps(id, uuid, timestamp, log_tag, item_type, item_size, getDevice()));
                     } else if (uuid.equals(UUID_ZERO) && log_tag == 83) {
                         mDatalogSessions.put(id, new DatalogSessionHealthSleep(id, uuid, timestamp, log_tag, item_type, item_size, getDevice()));