Add auto-complete suggestion to input variable

Use the lowest-level name of the last attribute. There was already logic for
doing auto-insertion when the user enters a <, so this works as John requested.

Author: garfieldnate

src/main/java/edu/umich/soar/visualsoar/ruleeditor/RuleEditor.java

@@ -1587,18 +1587,15 @@ public void actionPerformed(ActionEvent e) {
         }
     }
 
-	/**
-     * A simplified version of the TabCompleteAction that only displays
-     * the next possible attribute in the feedback window following the user
-     * typing a dot/period.
-     * Unlike the TabCompleteAction, this action does not ever insert anything
-     * into the rule editor, it only displays the attribute options in the feedback window.
-     * It also runs auto-justification.
-     */
-    class AutoSoarCompleteAction extends AbstractAction {
-        private static final long serialVersionUID = 20221225L;
-		private final EditorPane editorPane;
-		private final Toolkit toolkit;
+  /**
+   * Similar to TabCompleteAction, but it never auto-inserts text, and it auto-justifies the text.
+   * This is run automatically when the user types a dot or left angle bracket. It also runs
+   * auto-justification.
+   */
+  class AutoSoarCompleteAction extends AbstractAction {
+    private static final long serialVersionUID = 20221225L;
+    private final EditorPane editorPane;
+    private final Toolkit toolkit;
 
     public AutoSoarCompleteAction(EditorPane editorPane, Toolkit toolkit) {
       super("Auto Soar Complete");

src/main/java/edu/umich/soar/visualsoar/ruleeditor/SoarAutocomplete.java

@@ -13,11 +13,13 @@
 import org.jetbrains.annotations.Nullable;
 
 import java.io.StringReader;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 
+// TODO: Next: Write some tests. For variables, be sure to test "^ " (empty attribute name).
 public class SoarAutocomplete {
 
   /**
@@ -87,7 +89,8 @@ else if (!periodMustBeMostSignificant
   private static AutocompleteContext valueComplete(
       String userType, String prodSoFar, String fullText, OperatorNode associatedNode)
       throws ParseException {
-    List<String> completeMatches = getValueMatches(prodSoFar, fullText, associatedNode);
+    List<String> completeMatches = getVariableMatches(prodSoFar);
+    completeMatches.addAll(getValueMatches(prodSoFar, fullText, associatedNode));
     return new AutocompleteContext(userType, completeMatches);
   }
 
@@ -132,6 +135,24 @@ private static List<String> getAttributeMatches(
     return completeMatches;
   }
 
+  private static List<String> getVariableMatches(String prodSoFar) {
+    // given logic in caller, we know for a fact that there is a caret and a space, maybe a period
+    int attStart = prodSoFar.lastIndexOf("^");
+    int period = prodSoFar.lastIndexOf(".");
+    if (period > attStart) {
+      attStart = period;
+    }
+    attStart += 1;
+    int attEnd = prodSoFar.lastIndexOf(" <$$>");
+
+    String attName = prodSoFar.substring(attStart, attEnd);
+    List<String> variableMatches = new ArrayList<>();
+    if (!attName.isEmpty()) {
+      variableMatches.add("<" + attName + ">");
+    }
+    return variableMatches;
+  }
+
   /**
    * Retrieves the strings associated with entries in the datamap with values that match the user's
    * current production.