Set diagnosis key risk level based on day (#146)

* apply risk level to diagnosis keys based on day from static vector
* day 0 is „today“, which is not available right away from the framework.

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/util/ProtoFormatConverterExtensions.kt

@@ -9,18 +9,44 @@ object ProtoFormatConverterExtensions {
 
     private const val ROLLING_PERIOD = 144
     private const val DEFAULT_TRANSMISSION_RISK_LEVEL = 1
+    private const val TRANSMISSION_RISK_DAY_0 = 5
+    private const val TRANSMISSION_RISK_DAY_1 = 6
+    private const val TRANSMISSION_RISK_DAY_2 = 7
+    private const val TRANSMISSION_RISK_DAY_3 = 8
+    private const val TRANSMISSION_RISK_DAY_4 = 7
+    private const val TRANSMISSION_RISK_DAY_5 = 5
+    private const val TRANSMISSION_RISK_DAY_6 = 3
+    private const val TRANSMISSION_RISK_DAY_7 = 2
+    private val DEFAULT_TRANSMISSION_RISK_VECTOR = intArrayOf(
+        TRANSMISSION_RISK_DAY_0,
+        TRANSMISSION_RISK_DAY_1,
+        TRANSMISSION_RISK_DAY_2,
+        TRANSMISSION_RISK_DAY_3,
+        TRANSMISSION_RISK_DAY_4,
+        TRANSMISSION_RISK_DAY_5,
+        TRANSMISSION_RISK_DAY_6,
+        TRANSMISSION_RISK_DAY_7)
     private const val MAXIMUM_KEYS = 14
 
     fun List<TemporaryExposureKey>.limitKeyCount() =
-        this.sortedWith(compareBy({ it.rollingStartIntervalNumber })).asReversed().take(MAXIMUM_KEYS)
+        this.sortedWith(compareBy { it.rollingStartIntervalNumber }).asReversed().take(MAXIMUM_KEYS)
 
-    fun List<TemporaryExposureKey>.transformKeyHistoryToExternalFormat() = this.map {
-        KeyExportFormat.TemporaryExposureKey.newBuilder()
-            .setKeyData(ByteString.readFrom(it.keyData.inputStream()))
-            .setRollingStartIntervalNumber(it.rollingStartIntervalNumber)
-            .setRollingPeriod(ROLLING_PERIOD)
-            .setTransmissionRiskLevel(DEFAULT_TRANSMISSION_RISK_LEVEL)
-            .build()
+    fun List<TemporaryExposureKey>.transformKeyHistoryToExternalFormat() =
+        this.sortedWith(compareBy { it.rollingStartIntervalNumber })
+            .mapIndexed { index, it ->
+                // The earliest key we receive is from yesterday (i.e. 1 day ago),
+                // thus we need use index+1
+                val riskValue =
+                    if (index + 1 <= DEFAULT_TRANSMISSION_RISK_VECTOR.lastIndex)
+                        DEFAULT_TRANSMISSION_RISK_VECTOR[index + 1]
+                    else
+                        DEFAULT_TRANSMISSION_RISK_LEVEL
+                KeyExportFormat.TemporaryExposureKey.newBuilder()
+                    .setKeyData(ByteString.readFrom(it.keyData.inputStream()))
+                    .setRollingStartIntervalNumber(it.rollingStartIntervalNumber)
+                    .setRollingPeriod(ROLLING_PERIOD)
+                    .setTransmissionRiskLevel(riskValue)
+                    .build()
     }
 
     fun AppleLegacyKeyExchange.Key.convertToGoogleKey(): KeyExportFormat.TemporaryExposureKey =