Added Kotlin implementation of the PI extraction simulation (#112)

snippets/formulae/pi-extraction.kt

@@ -0,0 +1,39 @@
+import java.time.Duration
+import kotlin.math.*
+
+private const val SEC = 10000000L
+
+/**
+ * @param baseValue This is the "qty_per_cycle" value as returned by ESI
+ * @param cycleDuration Cycle duration, e.g. 2 hours
+ * @param length The number of cycles in this extraction
+ */
+fun calculateExtractorValues(baseValue: Int, cycleDuration: Duration, length: Int): List<Long> {
+    return buildList {
+        val startTime = 0L
+        val cycleTime = cycleDuration.toSeconds() * SEC
+        for (i in 0 until length) {
+            val currentTime = (i + 1) * cycleTime
+            add(calculateExtractorValue(baseValue, startTime, currentTime, cycleTime))
+        }
+    }
+}
+
+private fun calculateExtractorValue(baseValue: Int, startTime: Long, currentTime: Long, cycleTime: Long): Long {
+    val decayFactor = 0.012
+    val noiseFactor = 0.8
+    val cycleNum = max((currentTime - startTime + SEC) / cycleTime - 1, 0)
+    val barWidth = cycleTime / SEC / 900.0
+    val t = (cycleNum + 0.5) * barWidth
+    val decayValue = baseValue / (1 + t * decayFactor)
+    val phaseShift = baseValue.toDouble().pow(0.7)
+    val sinA = cos(phaseShift + t * (1.0 / 12.0))
+    val sinB = cos(phaseShift / 2.0 + t * (1.0 / 5.0))
+    val sinC = cos(t * (1.0 / 2.0))
+    val sinStuff = max(0.0, (sinA + sinB + sinC) / 3.0)
+    val barHeight = decayValue * (1 + noiseFactor * sinStuff)
+
+    val output = barWidth * barHeight
+    // Round down, with integers also rounded down (123.0 -> 122)
+    return if (output - output.toLong() == 0.0) output.toLong() - 1 else output.toLong()
+}