Fix all par index bug

richtextfx/src/integrationTest/java/org/fxmisc/richtext/TextBuildingUtils.java

@@ -0,0 +1,22 @@
+package org.fxmisc.richtext;
+
+import java.util.function.Function;
+
+public class TextBuildingUtils {
+
+    private TextBuildingUtils() {
+        throw new IllegalStateException("Cannot construct an instance of TextBuildingUtils");
+    }
+
+    /** Builds {@code totalNumber} of lines that each have the index of the line as their text */
+    public static String buildLines(int totalNumber) { return buildLines(totalNumber, String::valueOf); }
+
+    public static String buildLines(int totalNumber, Function<Integer, String> textOnEachLine) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < totalNumber - 1; i++) {
+            sb.append(textOnEachLine.apply(i)).append("\n");
+        }
+        sb.append(textOnEachLine.apply(totalNumber));
+        return sb.toString();
+    }
+}

richtextfx/src/integrationTest/java/org/fxmisc/richtext/api/ParagraphIndexMappingTests.java

@@ -0,0 +1,42 @@
+package org.fxmisc.richtext.api;
+
+import javafx.stage.Stage;
+import org.fxmisc.richtext.InlineCssTextAreaAppTest;
+import org.fxmisc.richtext.TextBuildingUtils;
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+
+public class ParagraphIndexMappingTests extends InlineCssTextAreaAppTest {
+
+    private static final int TOTAL_NUMBER_OF_LINES = 80;
+    private static final int LAST_PAR_INDEX = TOTAL_NUMBER_OF_LINES - 1;
+    private static final String CONTENT = TextBuildingUtils.buildLines(TOTAL_NUMBER_OF_LINES);
+
+    @Override
+    public void start(Stage stage) throws Exception {
+        super.start(stage);
+        area.replaceText(CONTENT);
+    }
+
+    @Test
+    public void all_par_to_visible_par_index_is_correct() {
+        interact(() -> area.showParagraphAtTop(0));
+        assertEquals(Optional.of(0), area.allParToVisibleParIndex(0));
+
+        interact(() -> area.showParagraphAtBottom(LAST_PAR_INDEX));
+        assertEquals(Optional.of(area.getVisibleParagraphs().size() - 1), area.allParToVisibleParIndex(LAST_PAR_INDEX));
+    }
+
+    @Test
+    public void visible_par_to_all_par_index_is_correct() {
+        interact(() -> area.showParagraphAtTop(0));
+        assertEquals(0, area.visibleParToAllParIndex(0));
+
+        interact(() -> area.showParagraphAtBottom(LAST_PAR_INDEX));
+        assertEquals(LAST_PAR_INDEX, area.visibleParToAllParIndex(area.getVisibleParagraphs().size() - 1));
+
+    }
+}

richtextfx/src/integrationTest/java/org/fxmisc/richtext/keyboard/PageUpDownTests.java

@@ -3,6 +3,7 @@
 import javafx.geometry.Bounds;
 import javafx.stage.Stage;
 import org.fxmisc.richtext.InlineCssTextAreaAppTest;
+import org.fxmisc.richtext.TextBuildingUtils;
 import org.junit.Test;
 
 import static javafx.scene.input.KeyCode.PAGE_DOWN;
@@ -13,17 +14,7 @@
 
 public class PageUpDownTests extends InlineCssTextAreaAppTest {
 
-    private static final String EIGHT_LINES;
-
-    static {
-        StringBuilder sb = new StringBuilder();
-        int totalLines = 8;
-        for (int i = 0; i < totalLines - 1; i++) {
-            sb.append(i).append("\n");
-        }
-        sb.append(totalLines);
-        EIGHT_LINES = sb.toString();
-    }
+    private static final String EIGHT_LINES = TextBuildingUtils.buildLines(8);
 
     @Override
     public void start(Stage stage) throws Exception {

richtextfx/src/main/java/org/fxmisc/richtext/GenericStyledArea.java

@@ -792,9 +792,9 @@ public final double getViewportHeight() {
     @Override
     public final Optional<Integer> allParToVisibleParIndex(int allParIndex) {
         if (allParIndex < 0) {
-            throw new IllegalArgumentException("Visible paragraph index cannot be negative but was " + allParIndex);
+            throw new IllegalArgumentException("The given paragraph index (allParIndex) cannot be negative but was " + allParIndex);
         }
-        if (allParIndex >= getVisibleParagraphs().size()) {
+        if (allParIndex >= getParagraphs().size()) {
             throw new IllegalArgumentException(String.format(
                     "Paragraphs' last index is [%s] but allParIndex was [%s]",
                     getParagraphs().size() - 1, allParIndex)