TrendArrow calculation

app/src/main/java/info/nightscout/androidaps/plugins/general/overview/OverviewFragment.kt

@@ -109,6 +109,7 @@ class OverviewFragment : DaggerFragment(), View.OnClickListener, OnLongClickList
     @Inject lateinit var fabricPrivacy: FabricPrivacy
     @Inject lateinit var overviewMenus: OverviewMenus
     @Inject lateinit var skinProvider: SkinProvider
+    @Inject lateinit var trendCalculator: TrendCalculator
     @Inject lateinit var config: Config
     @Inject lateinit var dateUtil: DateUtil
     @Inject lateinit var databaseHelper: DatabaseHelperInterface
@@ -584,7 +585,7 @@ class OverviewFragment : DaggerFragment(), View.OnClickListener, OnLongClickList
 
             binding.infoLayout.bg.text = lastBG.valueToUnitsString(units)
             binding.infoLayout.bg.setTextColor(color)
-            binding.infoLayout.arrow.setImageResource(lastBG.trendArrow.directionToIcon())
+            binding.infoLayout.arrow.setImageResource(trendCalculator.getTrendArrow(lastBG).directionToIcon())
             binding.infoLayout.arrow.setColorFilter(color)
 
             val glucoseStatus = GlucoseStatus(injector).glucoseStatusData

app/src/main/java/info/nightscout/androidaps/utils/TrendCalculator.kt

@@ -0,0 +1,45 @@
+package info.nightscout.androidaps.utils
+
+import info.nightscout.androidaps.database.AppRepository
+import info.nightscout.androidaps.database.entities.GlucoseValue
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+class TrendCalculator @Inject constructor(
+    private val repository: AppRepository
+) {
+
+    fun getTrendArrow(glucoseValue: GlucoseValue): GlucoseValue.TrendArrow =
+        if (glucoseValue.trendArrow != GlucoseValue.TrendArrow.NONE) glucoseValue.trendArrow
+        else calculateDirection(glucoseValue)
+
+    private fun calculateDirection(glucoseValue: GlucoseValue): GlucoseValue.TrendArrow {
+
+        val toTime = glucoseValue.timestamp
+        val readings = repository.compatGetBgReadingsDataFromTime(toTime - T.mins(10).msecs(), toTime, false).blockingGet()
+
+        if (readings.size < 2)
+            return GlucoseValue.TrendArrow.NONE
+        val current = readings[0]
+        val previous = readings[1]
+
+        // Avoid division by 0
+        val slope =
+            if (current.timestamp == previous.timestamp) 0.0
+            else (previous.value - current.value) / (previous.timestamp - current.timestamp)
+
+        val slopeByMinute = slope * 60000
+
+        return when {
+            slopeByMinute <= -3.5 -> GlucoseValue.TrendArrow.DOUBLE_DOWN
+            slopeByMinute <= -2   -> GlucoseValue.TrendArrow.SINGLE_DOWN
+            slopeByMinute <= -1   -> GlucoseValue.TrendArrow.FORTY_FIVE_DOWN
+            slopeByMinute <= 1    -> GlucoseValue.TrendArrow.FLAT
+            slopeByMinute <= 2    -> GlucoseValue.TrendArrow.FORTY_FIVE_UP
+            slopeByMinute <= 3.5  -> GlucoseValue.TrendArrow.SINGLE_UP
+            slopeByMinute <= 40   -> GlucoseValue.TrendArrow.DOUBLE_UP
+            else                  -> GlucoseValue.TrendArrow.NONE
+        }
+    }
+}