From e9212c0c11b40de0ddf31b3e84ff000f825895b4 Mon Sep 17 00:00:00 2001
From: zepumph <michael.kauzmann@colorado.edu>
Date: Mon, 11 Nov 2019 12:39:34 -0900
Subject: [PATCH] GravityForceLabRulerDescriber to extend ISLCDescriber, add
 hotkey alerts, https://github.com/phetsims/gravity-force-lab/issues/138

---
 .../GravityForceLabA11yStrings.js             |  3 ++
 .../view/GravityForceLabScreenView.js         |  4 +--
 .../GravityForceLabRulerDescriber.js          | 36 ++++++++++++++++---
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/js/gravity-force-lab/GravityForceLabA11yStrings.js b/js/gravity-force-lab/GravityForceLabA11yStrings.js
index 4650648c..ac5a6a2c 100644
--- a/js/gravity-force-lab/GravityForceLabA11yStrings.js
+++ b/js/gravity-force-lab/GravityForceLabA11yStrings.js
@@ -276,6 +276,9 @@ define( require => {
     centersApartPattern: {
       value: 'Centers of spheres {{distanceAndUnits}} apart.'
     },
+    jumpCenterMassAlert: {
+      value: 'Ruler zero mark at center of {{object1}}. {{centersApart}}'
+    },
 
     // vertical ruler positions
     coveringM2: {
diff --git a/js/gravity-force-lab/view/GravityForceLabScreenView.js b/js/gravity-force-lab/view/GravityForceLabScreenView.js
index a14ed193..60e84bb6 100644
--- a/js/gravity-force-lab/view/GravityForceLabScreenView.js
+++ b/js/gravity-force-lab/view/GravityForceLabScreenView.js
@@ -263,8 +263,8 @@ define( require => {
       this.layoutBounds.bottom
     ];
 
-    const rulerDescriber = new GravityForceLabRulerDescriber( model.rulerPositionProperty, modelViewTransform,
-      rulerRegionPositions, positionDescriber );
+    const rulerDescriber = new GravityForceLabRulerDescriber( model, mass1AbbreviatedString, mass2AbbreviatedString,
+      modelViewTransform, rulerRegionPositions, positionDescriber );
 
     // @private - added to object for animation stepping
     const gravityForceLabRuler = new ISLCRulerNode(
diff --git a/js/gravity-force-lab/view/describers/GravityForceLabRulerDescriber.js b/js/gravity-force-lab/view/describers/GravityForceLabRulerDescriber.js
index 4de65578..6a134d3c 100644
--- a/js/gravity-force-lab/view/describers/GravityForceLabRulerDescriber.js
+++ b/js/gravity-force-lab/view/describers/GravityForceLabRulerDescriber.js
@@ -11,6 +11,8 @@ define( require => {
   // modules
   const gravityForceLab = require( 'GRAVITY_FORCE_LAB/gravityForceLab' );
   const GravityForceLabA11yStrings = require( 'GRAVITY_FORCE_LAB/gravity-force-lab/GravityForceLabA11yStrings' );
+  const ISLCDescriber = require( 'INVERSE_SQUARE_LAW_COMMON/view/describers/ISLCDescriber' );
+  const ISLCObjectEnum = require( 'INVERSE_SQUARE_LAW_COMMON/view/ISLCObjectEnum' );
   const ISLCQueryParameters = require( 'INVERSE_SQUARE_LAW_COMMON/ISLCQueryParameters' );
   const Range = require( 'DOT/Range' );
   const StringUtils = require( 'PHETCOMMON/util/StringUtils' );
@@ -23,6 +25,7 @@ define( require => {
   const moveKeyboardHintString = GravityForceLabA11yStrings.moveKeyboardHint.value;
   const gestureHintString = GravityForceLabA11yStrings.gestureHint.value;
   const keyboardReleaseHintString = GravityForceLabA11yStrings.keyboardReleaseHint.value;
+  const jumpCenterMassAlertString = GravityForceLabA11yStrings.jumpCenterMassAlert.value;
 
   const coveringM2String = GravityForceLabA11yStrings.coveringM2.value;
   const coveringM1String = GravityForceLabA11yStrings.coveringM1.value;
@@ -47,20 +50,24 @@ define( require => {
     RULER_VERTICAL_REGIONS.indexOf( justBelowCentersString ) );
   const SHOW_RULER_REGIONS = ISLCQueryParameters.showRulerRegions;
 
-  class GravityForceLabRulerDescriber {
+  class GravityForceLabRulerDescriber extends ISLCDescriber {
 
     /**
-     * @param {Property.<number>} rulerPositionProperty
+     * @param {GravityForceLabModel} model
+     * @param {string} object1Label
+     * @param {string} object2Label
      * @param {ModelViewTransform2} modelViewTransform
      * @param {Array.<number>} viewYPositions - a list of Y positions, least (top) to greatest (bottom)
      * @param {PositionDescriber} positionDescriber
      */
-    constructor( rulerPositionProperty, modelViewTransform, viewYPositions, positionDescriber ) {
+    constructor( model, object1Label, object2Label, modelViewTransform, viewYPositions, positionDescriber ) {
 
       assert && assert( RULER_VERTICAL_REGIONS.length === viewYPositions.length, 'Unexpected number of y positions' );
 
+      super( model, object1Label, object2Label );
+
       // @private
-      this.rulerPositionProperty = rulerPositionProperty;
+      this.rulerPositionProperty = model.rulerPositionProperty;
       this.modelViewTransform = modelViewTransform;
       this.positionDescriber = positionDescriber;
       this.viewYPositions = viewYPositions;
@@ -143,6 +150,27 @@ define( require => {
       return RULER_VERTICAL_REGIONS[ this.getVerticalRegionIndex() ];
     }
 
+    /**
+     * Get current vertical position when in home position. Should only be called when the ruler is currently in home
+     * position.
+     */
+    getHomePositionString() {
+      const currentRegion = this.getCurrentVerticalRegion();
+      assert && assert( currentRegion === inHomePositionString, 'getHomePositionString called when ruler not in home position' );
+      return currentRegion;
+    }
+
+    /**
+     * @public
+     * @returns {string}
+     */
+    getJumpCenterMassAlert() {
+      return StringUtils.fillIn( jumpCenterMassAlertString, {
+        centersApart: this.getCentersApartDistance(),
+        object1: this.getObjectLabelFromEnum( ISLCObjectEnum.OBJECT_ONE )
+      } );
+    }
+
     /**
      * @public
      */