Bug 1163245 - [Battery][Gonk] Implementation of battery discharging remaining time. r=dhylands

hal/gonk/GonkHal.cpp

@@ -632,6 +632,7 @@ GetCurrentBatteryInformation(hal::BatteryInformation* aBatteryInfo)
   if (aBatteryInfo->charging() != previousCharging){
     aBatteryInfo->remainingTime() = dom::battery::kUnknownRemainingTime;
     memset(&lastLevelChange, 0, sizeof(struct timespec));
+    remainingTime = 0.0;
   }
 
   if (aBatteryInfo->charging()) {
@@ -668,7 +669,37 @@ GetCurrentBatteryInformation(hal::BatteryInformation* aBatteryInfo)
     }
 
   } else {
-    aBatteryInfo->remainingTime() = dom::battery::kUnknownRemainingTime;
+    if (aBatteryInfo->level() == 0.0) {
+      aBatteryInfo->remainingTime() = dom::battery::kDefaultRemainingTime;
+    } else if (aBatteryInfo->level() != previousLevel){
+      if (lastLevelChange.tv_sec != 0) {
+        clock_gettime(CLOCK_MONOTONIC, &now);
+        dtime = now.tv_sec - lastLevelChange.tv_sec;
+        dlevel = previousLevel - aBatteryInfo->level();
+
+        if (dlevel <= 0.0) {
+          aBatteryInfo->remainingTime() = dom::battery::kUnknownRemainingTime;
+        } else {
+          remainingTime = (double) round(dtime / dlevel * aBatteryInfo->level());
+          aBatteryInfo->remainingTime() = remainingTime;
+        }
+
+        lastLevelChange = now;
+      } else { // lastLevelChange.tv_sec == 0
+        clock_gettime(CLOCK_MONOTONIC, &lastLevelChange);
+        aBatteryInfo->remainingTime() = dom::battery::kUnknownRemainingTime;
+      }
+
+    } else {
+      clock_gettime(CLOCK_MONOTONIC, &now);
+      dtime = now.tv_sec - lastLevelChange.tv_sec;
+      if (dtime < remainingTime) {
+        aBatteryInfo->remainingTime() = round(remainingTime - dtime);
+      } else {
+        aBatteryInfo->remainingTime() = dom::battery::kUnknownRemainingTime;
+      }
+
+    }
   }
 
   previousCharging = aBatteryInfo->charging();