fix LastTimeRingBuffer

client/app/src/main/java/com/birdthedeveloper/prometheus/android/prometheus/android/exporter/worker/RemoteWriteSender.kt

@@ -22,33 +22,41 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.withContext
+import java.lang.IndexOutOfBoundsException
+import kotlin.math.abs
 
 private const val TAG: String = "REMOTE_WRITE_SENDER"
 
 // This class stores information about scrapes to PROM_SERVER and PUSHPROX
 // for purposes of scraping metrics on device and back-filling them later using remote write
 //
-// Only timestamps of succesfull scrapes are stored
+// Only timestamps of successful scrapes are stored
 internal class LastTimeRingBuffer(private val scrapeIntervalMs: Int) {
     private val buffer: Array<Long> = Array(hysteresisThreshold) { 0 }
-    private var firstIndex: Int = 0
+    private var firstIndex: Int = -1
 
     companion object {
         private const val hysteresisThreshold: Int = 3
     }
 
     fun setLastTime(timestamp: Long) {
-        firstIndex = firstIndex++ % hysteresisThreshold
+        firstIndex = (++firstIndex) % hysteresisThreshold
         buffer[firstIndex] = timestamp
+        System.out.println("${buffer[0]} ${buffer[1]} ${buffer[2]}")
+        System.out.flush()
     }
 
     fun getTimeByIndex(index: Int): Long {
         if (index > hysteresisThreshold - 1) {
-            throw IllegalArgumentException("index cannot be bigger than hysteresisThreshold")
+            throw IndexOutOfBoundsException("index cannot be bigger than hysteresisThreshold")
         }
 
-        val bufferIndex: Int = firstIndex + index % hysteresisThreshold
-        return buffer[bufferIndex]
+        val bufferIndex: Int = (firstIndex - index)
+        return if (bufferIndex < 0){
+            buffer[hysteresisThreshold + bufferIndex]
+        }else{
+            buffer[bufferIndex]
+        }
     }
 
     fun checkScrapeDidNotHappenInTime(): Boolean {
@@ -64,7 +72,6 @@ internal class LastTimeRingBuffer(private val scrapeIntervalMs: Int) {
         }
         return false
     }
-
 }
 
 data class RemoteWriteConfiguration(

client/app/src/test/java/com/birdthedeveloper/prometheus/android/prometheus/android/exporter/ExampleUnitTest.kt

@@ -1,17 +0,0 @@
-package com.birdthedeveloper.prometheus.android.prometheus.android.exporter
-
-import org.junit.Test
-
-import org.junit.Assert.*
-
-/**
- * Example local unit test, which will execute on the development machine (host).
- *
- * See [testing documentation](http://d.android.com/tools/testing).
- */
-class ExampleUnitTest {
-    @Test
-    fun addition_isCorrect() {
-        assertEquals(4, 2 + 2)
-    }
-}

client/app/src/test/java/com/birdthedeveloper/prometheus/android/prometheus/android/exporter/worker/LastTimeRingBufferTest.kt

@@ -9,13 +9,33 @@ class LastTimeRingBufferTest {
 
     @Test
     fun `basic test of LastTimeRingBuffer`() {
-        val lastTimeBuffer = LastTimeRingBuffer(10)
-        assertEquals(0, lastTimeBuffer.getTimeByIndex(0))
+        val lastTimeRingBuffer = LastTimeRingBuffer(10)
+        assertEquals(0, lastTimeRingBuffer.getTimeByIndex(0))
 
-        lastTimeBuffer.setLastTime(2L)
-        lastTimeBuffer.setLastTime(5L)
+        lastTimeRingBuffer.setLastTime(2L)
+        lastTimeRingBuffer.setLastTime(5L)
 
-        //assertEquals(5, lastTimeBuffer.getTimeByIndex(0))
-        //assertEquals(2, lastTimeBuffer.getTimeByIndex(1))
+        assertEquals(5, lastTimeRingBuffer.getTimeByIndex(0))
     }
-}
+
+    @Test
+    fun `ring buffer test`() {
+        val lastTimeRingBuffer = LastTimeRingBuffer(10)
+
+        for (i in 1..4){
+            lastTimeRingBuffer.setLastTime(i.toLong())
+        }
+
+        assertEquals(4, lastTimeRingBuffer.getTimeByIndex(0))
+        assertEquals(3, lastTimeRingBuffer.getTimeByIndex(1))
+        assertEquals(2, lastTimeRingBuffer.getTimeByIndex(2))
+    }
+
+    @Test
+    fun `getTimeByIndex throws exception on out-of-bounds index`(){
+        val lastTimeRingBuffer = LastTimeRingBuffer(10)
+        assertThrows(IndexOutOfBoundsException::class.java){
+            lastTimeRingBuffer.getTimeByIndex(Int.MAX_VALUE / 3)
+        }
+    }
+}