fix: restore the initial line on key down

Author: javier-godoy

src/main/java/com/flowingcode/vaadin/addons/xterm/TerminalHistory.java

@@ -32,6 +32,8 @@ public class TerminalHistory implements Serializable {
 
   private String lastRet;
 
+  private String initialLine;
+
   private Integer maxSize;
 
   protected <T extends XTermBase & ITerminalConsole> TerminalHistory(T terminal) {
@@ -93,7 +95,14 @@ public boolean isEnabled() {
   }
 
   private void handleArrowUp() {
-    write(previous());
+    if (initialLine == null) {
+      ((ITerminalConsole) terminal).getCurrentLine().thenAccept(currentLine -> {
+        initialLine = currentLine;
+        write(previous());
+      });
+    } else {
+      write(previous());
+    }
   }
 
   private void handleArrowDown() {
@@ -161,6 +170,7 @@ public void add(String line) {
 
   private void setCurrentLine(String currentLine) {
     if (!currentLine.equals(lastRet)) {
+      initialLine = currentLine;
       prefix = currentLine;
       iterator = null;
     }
@@ -181,7 +191,11 @@ private String previous() {
   }
 
   private String next() {
-    return find(forwardIterator(), line -> true).orElse("");
+    return find(forwardIterator(), line -> true).orElseGet(() -> {
+      String result = initialLine;
+      initialLine = null;
+      return result;
+    });
   }
 
   private String findPrevious(String currentLine) {

src/test/java/com/flowingcode/vaadin/addons/xterm/integration/TerminalHistoryIT.java

@@ -40,6 +40,27 @@ public void testArrowKeys() {
     assertThat(currentLine(term), isEmptyString());
   }
 
+  @Test
+  public void testArrowKeysAndRestore() {
+    TestBenchElement term = $("fc-xterm").first();
+
+    WebElement input = (WebElement) waitUntil(driver -> ((HasTestBenchCommandExecutor) driver)
+        .getCommandExecutor().executeScript("return arguments[0].terminal.textarea", term));
+
+    int y = cursorPosition(term).y;
+    input.sendKeys("foo1\nfoo2\n");
+
+    assertThat(cursorPosition(term), is(at(0, y += 2)));
+    assertThat(lineAtOffset(term, 0), isEmptyString());
+
+    input.sendKeys("bar");
+    input.sendKeys(Keys.ARROW_UP);
+    assertThat(currentLine(term), is("foo2"));
+
+    input.sendKeys(Keys.ARROW_DOWN);
+    assertThat(currentLine(term), is("bar"));
+  }
+
   @Test
   public void testPageUpDown() {
     TestBenchElement term = $("fc-xterm").first();