From 9b0fd8892907a596f208d5b72aa1df7adb77bd66 Mon Sep 17 00:00:00 2001
From: Luisav1 <luisa.vargassuarez@ucalgary.ca>
Date: Tue, 1 Aug 2023 09:23:37 -0600
Subject: [PATCH] Create function to extract particle closest to atom center.
 See https://github.com/phetsims/build-a-nucleus/issues/97.

---
 js/model/ParticleAtom.ts | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/js/model/ParticleAtom.ts b/js/model/ParticleAtom.ts
index 2ba7ad8..987b889 100644
--- a/js/model/ParticleAtom.ts
+++ b/js/model/ParticleAtom.ts
@@ -437,6 +437,41 @@ class ParticleAtom extends PhetioObject {
     return particle as unknown as Particle;
   }
 
+  public extractParticleClosestToCenter( particleType: ParticleTypeString ): Particle {
+    let particle = null;
+    switch( particleType ) {
+      case 'proton':
+        if ( this.protons.length > 0 ) {
+          particle = _.sortBy( [ ...this.protons ], proton =>
+            proton.positionProperty.value.distance( this.positionProperty.value ) )[ 0 ];
+        }
+        break;
+
+      case 'neutron':
+        if ( this.neutrons.length > 0 ) {
+          particle = _.sortBy( [ ...this.neutrons ], neutron =>
+            neutron.positionProperty.value.distance( this.positionProperty.value ) )[ 0 ];
+        }
+        break;
+
+      case 'electron':
+        if ( this.electrons.length > 0 ) {
+          particle = _.sortBy( [ ...this.electrons ], electron =>
+            electron.positionProperty.value.distance( this.positionProperty.value ) )[ 0 ];
+        }
+        break;
+
+      default:
+        throw new Error( 'Attempt to remove unknown particle type.' );
+    }
+
+    if ( particle !== null ) {
+      this.removeParticle( particle );
+    }
+
+    return particle as unknown as Particle;
+  }
+
   /**
    * Remove all the particles but don't reconfigure the nucleus as they go. This makes it a quicker operation.
    */