From ae16f62a313f4558e5fdae86f118e06cb7f0cc14 Mon Sep 17 00:00:00 2001
From: jbphet <jpblanco@yahoo.com>
Date: Fri, 21 Jul 2023 14:13:40 -0600
Subject: [PATCH] added common function for detecting energy packets crossing
 an altitude, see https://github.com/phetsims/greenhouse-effect/issues/337

---
 js/common/model/EnergyAbsorbingEmittingLayer.ts |  5 ++---
 js/common/model/FluxSensor.ts                   | 12 ++----------
 js/common/model/energyPacketCrossedAltitude.ts  | 17 +++++++++++++++++
 3 files changed, 21 insertions(+), 13 deletions(-)
 create mode 100644 js/common/model/energyPacketCrossedAltitude.ts

diff --git a/js/common/model/EnergyAbsorbingEmittingLayer.ts b/js/common/model/EnergyAbsorbingEmittingLayer.ts
index 38be442e..598f48cc 100644
--- a/js/common/model/EnergyAbsorbingEmittingLayer.ts
+++ b/js/common/model/EnergyAbsorbingEmittingLayer.ts
@@ -18,6 +18,7 @@ import GreenhouseEffectConstants from '../GreenhouseEffectConstants.js';
 import EMEnergyPacket from './EMEnergyPacket.js';
 import EnergyDirection from './EnergyDirection.js';
 import WithRequired from '../../../../phet-core/js/types/WithRequired.js';
+import energyPacketCrossedAltitude from './energyPacketCrossedAltitude.js';
 
 // constants
 
@@ -173,9 +174,7 @@ class EnergyAbsorbingEmittingLayer extends PhetioObject {
    * Returns true if the provided energy packet crossed over this layer during its latest step.
    */
   protected energyPacketCrossedThisLayer( energyPacket: EMEnergyPacket ): boolean {
-    const altitude = this.altitude;
-    return ( energyPacket.previousAltitude > altitude && energyPacket.altitude <= altitude ) ||
-           ( energyPacket.previousAltitude < altitude && energyPacket.altitude >= altitude );
+    return energyPacketCrossedAltitude( energyPacket, this.altitude );
   }
 
   /**
diff --git a/js/common/model/FluxSensor.ts b/js/common/model/FluxSensor.ts
index f6ebbd69..4ec115a8 100644
--- a/js/common/model/FluxSensor.ts
+++ b/js/common/model/FluxSensor.ts
@@ -19,6 +19,7 @@ import optionize from '../../../../phet-core/js/optionize.js';
 import PhetioObject, { PhetioObjectOptions } from '../../../../tandem/js/PhetioObject.js';
 import greenhouseEffect from '../../greenhouseEffect.js';
 import EMEnergyPacket from './EMEnergyPacket.js';
+import energyPacketCrossedAltitude from './energyPacketCrossedAltitude.js';
 import EnergyDirection from './EnergyDirection.js';
 import EnergyRateTracker from './EnergyRateTracker.js';
 import LayersModel from './LayersModel.js';
@@ -129,7 +130,7 @@ class FluxSensor extends PhetioObject {
 
     // Go through each energy packet and determine if it has moved through the sensor and, if so, measure it.
     energyPackets.forEach( energyPacket => {
-      if ( this.energyPacketCrossedAltitude( energyPacket ) ) {
+      if ( energyPacketCrossedAltitude( energyPacket, this.altitudeProperty.value ) ) {
         if ( energyPacket.direction === EnergyDirection.DOWN ) {
           assert && assert( energyPacket.isVisible || energyPacket.isInfrared, 'energy packet must be visible or IR' );
           if ( energyPacket.isVisible ) {
@@ -187,15 +188,6 @@ class FluxSensor extends PhetioObject {
     this.clearEnergyTrackers();
     this.altitudeProperty.reset();
   }
-
-  /**
-   * Returns true if the provided energy packet passed through the altitude at which this sensor resides.
-   */
-  private energyPacketCrossedAltitude( energyPacket: EMEnergyPacket ): boolean {
-    const altitude = this.altitudeProperty.value;
-    return ( energyPacket.previousAltitude > altitude && energyPacket.altitude <= altitude ) ||
-           ( energyPacket.previousAltitude < altitude && energyPacket.altitude >= altitude );
-  }
 }
 
 greenhouseEffect.register( 'FluxSensor', FluxSensor );
diff --git a/js/common/model/energyPacketCrossedAltitude.ts b/js/common/model/energyPacketCrossedAltitude.ts
new file mode 100644
index 00000000..8713887e
--- /dev/null
+++ b/js/common/model/energyPacketCrossedAltitude.ts
@@ -0,0 +1,17 @@
+// Copyright 2023, University of Colorado Boulder
+
+import EMEnergyPacket from './EMEnergyPacket.js';
+
+/**
+ * A utility function for testing whether an energy packet has crossed through the provided altitude in either the
+ * upward or downward moving direction.
+ *
+ * @author John Blanco (PhET Interactive Simulations)
+ */
+
+const energyPacketCrossedAltitude = ( energyPacket: EMEnergyPacket, altitude: number ): boolean => {
+  return ( energyPacket.previousAltitude > altitude && energyPacket.altitude <= altitude ) ||
+         ( energyPacket.previousAltitude < altitude && energyPacket.altitude >= altitude );
+};
+
+export default energyPacketCrossedAltitude;
\ No newline at end of file