From b730aa26200d169c4c9d544b50cd785d7f7bc33f Mon Sep 17 00:00:00 2001
From: Michael Barlow <m.barlow12@gmail.com>
Date: Tue, 11 Dec 2018 20:27:45 -0700
Subject: [PATCH] move createAriaValueText implementation to screenView, mirror
 implementation from GFL see commits in phetsims/gravity-force-lab#124

---
 .../view/GravityForceLabBasicsMassNode.js     | 14 ++--
 .../view/GravityForceLabBasicsScreenView.js   | 79 ++++++++++++++++++-
 2 files changed, 83 insertions(+), 10 deletions(-)

diff --git a/js/gravity-force-lab-basics/view/GravityForceLabBasicsMassNode.js b/js/gravity-force-lab-basics/view/GravityForceLabBasicsMassNode.js
index 45e4c55..3d3356f 100644
--- a/js/gravity-force-lab-basics/view/GravityForceLabBasicsMassNode.js
+++ b/js/gravity-force-lab-basics/view/GravityForceLabBasicsMassNode.js
@@ -46,12 +46,7 @@ define( function( require ) {
       y: MASS_NODE_Y_POSITION,
       snapToNearest: model.snapObjectsToNearest, // in meters, charges will snap to the nearest 0.1 meters in model coordinates
 
-      tandem: Tandem.required,
-
-      // a11y
-      createAriaValueText: function( formattedValue, previousValue ) {
-        return stringManager.getSpherePositionAriaValueText( formattedValue, self );
-      }
+      tandem: Tandem.required
     }, options );
 
     // @private
@@ -84,8 +79,11 @@ define( function( require ) {
     },
 
     resetAriaValueText: function() {
-      var position = this.objectModel.positionProperty.get();
-      this.ariaValueText = this.stringManager.getSpherePositionAndRegionText( position, this.enum );
+      if ( this.objectModel.isAtEdgeOfRange() ) {
+        this.ariaValueText = this.stringManager.getLastStopDistanceFromOtherObjectText( this.enum );
+        return;
+      }
+      this.ariaValueText = this.stringManager.getPositionAndDistanceFromOtherObjectText( this.enum );
       // position = Util.toFixedNumber( ( position + 4800 ) / 1e3, 1 );
       // this.ariaValueText = GFLBStringManager.getPositionMeterMarkText( `${position} kilometer reset` );
     }
diff --git a/js/gravity-force-lab-basics/view/GravityForceLabBasicsScreenView.js b/js/gravity-force-lab-basics/view/GravityForceLabBasicsScreenView.js
index 3d02a7d..727b53f 100644
--- a/js/gravity-force-lab-basics/view/GravityForceLabBasicsScreenView.js
+++ b/js/gravity-force-lab-basics/view/GravityForceLabBasicsScreenView.js
@@ -35,9 +35,11 @@ define( function( require ) {
   var MassPDOMNode = require( 'GRAVITY_FORCE_LAB/gravity-force-lab/view/MassPDOMNode' );
   var ModelViewTransform2 = require( 'PHETCOMMON/view/ModelViewTransform2' );
   var Node = require( 'SCENERY/nodes/Node' );
+  var Property = require( 'AXON/Property' );
   var PlayAreaNode = require( 'SCENERY_PHET/accessibility/nodes/PlayAreaNode' );
   var ResetAllButton = require( 'SCENERY_PHET/buttons/ResetAllButton' );
   var ScreenView = require( 'JOIST/ScreenView' );
+  var Util = require( 'DOT/Util' );
   var Vector2 = require( 'DOT/Vector2' );
 
   // constants
@@ -106,6 +108,36 @@ define( function( require ) {
       .05
     );
 
+    // position state variables
+    var lastMoveCloser = false;
+    var movedCloser = false;
+    var distanceBetween = Math.abs( model.object2.positionProperty.get() - model.object1.positionProperty.get() );
+
+    function ariaValueTextCreator( objectEnum ) {
+      return function( formattedValue, oldValue ) {
+        var thisObjectEnum = objectEnum;
+        var thisObject = thisObjectEnum === OBJECT_ONE ? model.object1 : model.object2;
+        var newDistanceBetween = Math.abs( model.object1.positionProperty.get() - model.object2.positionProperty.get() );
+        newDistanceBetween = Util.toFixedNumber( newDistanceBetween, 1 );
+        var newAriaValueText = stringManager.getDistanceFromOtherObjectText( thisObjectEnum, newDistanceBetween );
+
+        movedCloser = newDistanceBetween < distanceBetween;
+
+        if ( lastMoveCloser !== movedCloser ) {
+          newAriaValueText = stringManager.getProgressPositionAndDistanceFromOtherObjectText( thisObjectEnum, movedCloser, newDistanceBetween );
+        }
+
+        if ( thisObject.isAtEdgeOfRange() ) {
+          // last stop
+          newAriaValueText = stringManager.getLastStopDistanceFromOtherObjectText( thisObjectEnum, newDistanceBetween );
+        }
+
+        lastMoveCloser = movedCloser;
+        distanceBetween = newDistanceBetween;
+        return newAriaValueText;
+      };
+    }
+
     // add the mass nodes to the view
     var mass1Node = new GravityForceLabBasicsMassNode( model, model.object1, this.layoutBounds, stringManager, modelViewTransform, {
       label: mass1LabelString,
@@ -113,7 +145,8 @@ define( function( require ) {
       defaultDirection: 'left',
       arrowColor: '#66F',
       forceArrowHeight: 125,
-      tandem: tandem.createTandem( 'mass1Node' )
+      tandem: tandem.createTandem( 'mass1Node' ),
+      createAriaValueText: ariaValueTextCreator( OBJECT_ONE )
     } );
 
     var mass2Node = new GravityForceLabBasicsMassNode( model, model.object2, this.layoutBounds, stringManager, modelViewTransform, {
@@ -122,7 +155,8 @@ define( function( require ) {
       defaultDirection: 'right',
       arrowColor: '#F66',
       forceArrowHeight: 175,
-      tandem: tandem.createTandem( 'mass2Node' )
+      tandem: tandem.createTandem( 'mass2Node' ),
+      createAriaValueText: ariaValueTextCreator( OBJECT_TWO )
     } );
 
     playAreaNode.addChild( new MassPDOMNode( model, OBJECT_ONE, stringManager, {
@@ -243,6 +277,47 @@ define( function( require ) {
     // a11y - specify the order of focus for things in the ScreenView
     // this.accessibleOrder = [ mass1Node, mass2Node, massControlBox, parameterControlPanel, resetAllButton ];
 
+    Property.multilink(
+      [ model.object1.positionProperty, model.object2.positionProperty ],
+      function( x1, x2 ) {
+        var focusedMassNode;
+        var otherMassNode;
+        var distance = Util.toFixedNumber( Math.abs( x1 - x2 ), 1 );
+
+        if ( mass1Node.isFocused() ) {
+          focusedMassNode = mass1Node;
+          otherMassNode = mass2Node;
+        }
+        else if ( mass2Node.isFocused() ) {
+          focusedMassNode = mass2Node;
+          otherMassNode = mass1Node;
+        }
+        else {
+          // this case is possible if the radius of a mass pushes the other mass
+          mass1Node.ariaValueText = stringManager.getPositionAndDistanceFromOtherObjectText( OBJECT_ONE, distance );
+          mass2Node.ariaValueText = stringManager.getPositionAndDistanceFromOtherObjectText( OBJECT_TWO, distance );
+          return;
+        }
+
+        var newAriaValueText = stringManager.getPositionAndDistanceFromOtherObjectText( otherMassNode.enum, distance );
+
+        if ( focusedMassNode.objectModel.isAtEdgeOfRange() ) {
+          newAriaValueText = stringManager.getLastStopDistanceFromOtherObjectText( otherMassNode.enum, distance );
+        }
+        otherMassNode.ariaValueText = newAriaValueText;
+      }
+    );
+
+    function focusListenerCreator( objectNode ) {
+      return function( event ) {
+        lastMoveCloser = null;
+        objectNode.resetAriaValueText();
+      };
+    }
+
+    mass1Node.addInputListener( { focus: focusListenerCreator( mass1Node ) } );
+    mass2Node.addInputListener( { focus: focusListenerCreator( mass2Node ) } );
+
     //------------------------------------------------
     // debugging
     //------------------------------------------------