Start rewrite for thread safety, automatic stale element resolution

This is a huge refactoring motivated by:
- Wanting to move away from unnecessary dynamic proxies
- Needing thread safe access to driver
- Needing to automatically refind elements if they are stale
- Needing to have targeted drivers and elements
- Needing to add locator information to toString (not done yet, but now
  possible)

It works by creating various implementations of WebElement and WebDriver
that accomplish each of those above needs (more or less). This allows
each need to be focused and individually testable. On the downside, the
real driver is heavily nested, something like:

ThreadedWebDriver
  - driver: ForwardingTargetedWebDriver
    - driver: RefindingWebDriver
      - driver: FirefoxDriver -- real impl

Likewise with WebElements:

ThreadedWebElement
  - element: ForwardingTargetedWebElement
    - element: RefindingWebElement
      - element: RemoteWebElement -- real impl

On the plus side, none of those implementations have to know about any
other. Care must be taken in wiring them up the right way, however.

As of now, not everything is completely tested or verified, but the
fundamentals work.

Known issues:
- Lists of elements are not refinding. Not sure if it's possible.
  - Could/should at least create refinding element if list size == 1
  - Could use javascript to associate each element in the list
    with xpath, and use that to relook up individual elements, but this
    is a little scary.

src/main/java/com/redhat/darcy/webdriver/ElementConstructor.java

@@ -35,5 +35,5 @@
  */
 @FunctionalInterface
 public interface ElementConstructor<T extends Element> {
-    T newElement(Supplier<WebElement> source, ElementFactory converter);
+    T newElement(WebElement source, ElementFactory converter);
 }

src/main/java/com/redhat/darcy/webdriver/WebDriverBrowserFactory.java

@@ -29,6 +29,7 @@
 import com.redhat.darcy.webdriver.internal.TargetedWebDriver;
 import com.redhat.darcy.webdriver.internal.TargetedWebDriverFactory;
 import com.redhat.darcy.webdriver.internal.TargetedWebDriverParentContext;
+import com.redhat.darcy.webdriver.internal.ThreadSafeCachingTargetedWebDriverFactory;
 import com.redhat.darcy.webdriver.internal.WebDriverTarget;
 import com.redhat.darcy.webdriver.internal.WebDriverTargets;
 
@@ -63,8 +64,8 @@ public abstract <E extends WebDriverElement> T withElementImplementation(Class<?
     protected static Browser makeBrowser(WebDriver driver, ElementConstructorMap constructorMap) {
         WebDriverTarget target = WebDriverTargets.window(driver.getWindowHandle());
 
-        TargetedWebDriverFactory targetedWdFactory = new CachingTargetedWebDriverFactory(driver,
-                target);
+        TargetedWebDriverFactory targetedWdFactory = new ThreadSafeCachingTargetedWebDriverFactory(
+                driver, target);
         TargetedWebDriver targetedDriver = targetedWdFactory.getTargetedWebDriver(target);
 
         TargetedElementFactoryFactory elementFactoryFactory =

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverButton.java

@@ -24,11 +24,9 @@
 
 import org.openqa.selenium.WebElement;
 
-import java.util.function.Supplier;
-
 public class WebDriverButton extends WebDriverElement implements Button {
 
-    public WebDriverButton(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverButton(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverElement.java

@@ -21,23 +21,19 @@
 
 import com.redhat.darcy.ui.api.ElementContext;
 import com.redhat.darcy.ui.api.elements.Element;
-import com.redhat.darcy.util.Caching;
+import com.redhat.darcy.ui.api.elements.Findable;
 import com.redhat.darcy.webdriver.internal.DefaultWebDriverElementContext;
 import com.redhat.darcy.webdriver.internal.ElementFactory;
 
 import org.openqa.selenium.NotFoundException;
 import org.openqa.selenium.WebElement;
 import org.openqa.selenium.internal.WrapsElement;
 
-import java.util.function.Supplier;
-
-public class WebDriverElement implements Element, Caching, WrapsElement {
-    private final Supplier<WebElement> source;
+public class WebDriverElement implements Element, WrapsElement {
+    private final WebElement source;
     private final ElementFactory elementFactory;
 
-    private WebElement cachedElement;
-
-    public WebDriverElement(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverElement(WebElement source, ElementFactory elementFactory) {
         this.source = source;
         this.elementFactory = elementFactory;
     }
@@ -53,27 +49,12 @@ public boolean isDisplayed() {
 
     @Override
     public boolean isPresent() {
-        try {
-            invalidateCache();
-            getWrappedElement();
-            return true;
-        } catch (NotFoundException e) {
-            return false;
-        }
-    }
-
-    @Override
-    public void invalidateCache() {
-        cachedElement = null;
+        return ((Findable) source).isPresent();
     }
 
     @Override
     public WebElement getWrappedElement() {
-        if (cachedElement == null) {
-            cachedElement = source.get();
-        }
-
-        return cachedElement;
+        return source;
     }
 
     public ElementContext getElementContext() {

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverLabel.java

@@ -24,10 +24,8 @@
 
 import org.openqa.selenium.WebElement;
 
-import java.util.function.Supplier;
-
 public class WebDriverLabel extends WebDriverElement implements Label {
-    public WebDriverLabel(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverLabel(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverLink.java

@@ -24,10 +24,8 @@
 
 import org.openqa.selenium.WebElement;
 
-import java.util.function.Supplier;
-
 public class WebDriverLink extends WebDriverElement implements Link {
-    public WebDriverLink(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverLink(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverSelect.java

@@ -33,7 +33,7 @@
 
 public class WebDriverSelect extends WebDriverElement implements Select {
 
-    public WebDriverSelect(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverSelect(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverSelectOption.java

@@ -28,7 +28,7 @@
 
 public class WebDriverSelectOption extends WebDriverElement implements SelectOption {
 
-    public WebDriverSelectOption(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverSelectOption(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/elements/WebDriverTextInput.java

@@ -27,7 +27,7 @@
 import java.util.function.Supplier;
 
 public class WebDriverTextInput extends WebDriverElement implements TextInput {
-    public WebDriverTextInput(Supplier<WebElement> source, ElementFactory elementFactory) {
+    public WebDriverTextInput(WebElement source, ElementFactory elementFactory) {
         super(source, elementFactory);
     }
 

src/main/java/com/redhat/darcy/webdriver/internal/DefaultWebDriverElementContext.java

@@ -24,6 +24,7 @@
 import com.redhat.darcy.ui.api.Transition;
 import com.redhat.darcy.ui.api.elements.Element;
 import com.redhat.darcy.ui.internal.SimpleTransition;
+import com.redhat.darcy.util.LazyList;
 import com.redhat.darcy.webdriver.WebDriverElementContext;
 import com.redhat.darcy.webdriver.locators.ByPartialVisibleText;
 import com.redhat.darcy.webdriver.locators.ByVisibleText;
@@ -38,6 +39,7 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 public class DefaultWebDriverElementContext implements WebDriverElementContext {
     private final WebElementContext context;
@@ -69,7 +71,7 @@ public <T> List<T> findAllById(Class<T> type, String id) {
 
     @Override
     public <T> T findById(Class<T> type, String id) {
-        return newElement(type, () -> context.findById(WebElement.class, id));
+        return newElement(type, context.findById(WebElement.class, id));
     }
 
     @Override
@@ -79,7 +81,7 @@ public <T> List<T> findAllByName(Class<T> type, String name) {
 
     @Override
     public <T> T findByName(Class<T> type, String name) {
-        return newElement(type, () -> context.findByName(WebElement.class, name));
+        return newElement(type, context.findByName(WebElement.class, name));
     }
 
     @Override
@@ -89,7 +91,7 @@ public <T> List<T> findAllByLinkText(Class<T> type, String linkText) {
 
     @Override
     public <T> T findByLinkText(Class<T> type, String linkText) {
-        return newElement(type, () -> context.findByLinkText(WebElement.class, linkText));
+        return newElement(type, context.findByLinkText(WebElement.class, linkText));
     }
 
     @Override
@@ -100,7 +102,7 @@ public <T> List<T> findAllByTextContent(Class<T> type, String textContent) {
 
     @Override
     public <T> T findByTextContent(Class<T> type, String textContent) {
-        return newElement(type, () -> context.findByTextContent(WebElement.class, textContent));
+        return newElement(type, context.findByTextContent(WebElement.class, textContent));
     }
 
     @Override
@@ -112,7 +114,7 @@ public <T> List<T> findAllByPartialTextContent(Class<T> type, String partialText
     @Override
     public <T> T findByPartialTextContent(Class<T> type, String partialTextContent) {
         return newElement(type,
-                () -> context.findByPartialTextContent(WebElement.class, partialTextContent));
+                context.findByPartialTextContent(WebElement.class, partialTextContent));
     }
 
     @Override
@@ -122,7 +124,7 @@ public <T> List<T> findAllByXPath(Class<T> type, String xpath) {
 
     @Override
     public <T> T findByXPath(Class<T> type, String xpath) {
-        return newElement(type, () -> context.findByXPath(WebElement.class, xpath));
+        return newElement(type, context.findByXPath(WebElement.class, xpath));
     }
 
     @Override
@@ -132,7 +134,7 @@ public <T> List<T> findAllByCss(Class<T> type, String css) {
 
     @Override
     public <T> T findByCss(Class<T> type, String css) {
-        return newElement(type, () -> context.findByCss(WebElement.class, css));
+        return newElement(type, context.findByCss(WebElement.class, css));
     }
 
     @Override
@@ -142,7 +144,7 @@ public <T> List<T> findAllByHtmlTag(Class<T> type, String tag) {
 
     @Override
     public <T> T findByHtmlTag(Class<T> type, String tag) {
-        return newElement(type, () -> context.findByHtmlTag(WebElement.class, tag));
+        return newElement(type, context.findByHtmlTag(WebElement.class, tag));
     }
 
     @Override
@@ -152,7 +154,7 @@ public <T> List<T> findAllByChained(Class<T> type, Locator... locators) {
 
     @Override
     public <T> T findByChained(Class<T> type, Locator... locators) {
-        return newElement(type, () -> context.findByChained(WebElement.class, locators));
+        return newElement(type, context.findByChained(WebElement.class, locators));
     }
 
     @Override
@@ -162,7 +164,7 @@ public <T> List<T> findAllByNested(Class<T> type, Element parent, Locator child)
 
     @Override
     public <T> T findByNested(Class<T> type, Element parent, Locator child) {
-        return newElement(type, () -> context.findByNested(WebElement.class, parent, child));
+        return newElement(type, context.findByNested(WebElement.class, parent, child));
     }
 
     @Override
@@ -178,7 +180,7 @@ public WebDriverElementContext withRootElement(Element root) {
     }
 
     @SuppressWarnings("unchecked")
-    private <T> T newElement(Class<T> type, Supplier<WebElement> source) {
+    private <T> T newElement(Class<T> type, WebElement source) {
         if (!Element.class.isAssignableFrom(type)) {
             throw new DarcyException("An ElementContext can only locate Element types: "
                     + type.toString());
@@ -194,7 +196,10 @@ private <T> List<T> newElementList(Class<T> type, Supplier<List<WebElement>> sou
                     + type.toString());
         }
 
-        return (List<T>) elementFactory.newElementList((Class<Element>) type, source);
+        return new LazyList<>(() -> (List<T>) source.get()
+                .stream()
+                .map(s -> elementFactory.newElement((Class<Element>) type, s))
+                .collect(Collectors.toList()));
     }
 
     /**

src/main/java/com/redhat/darcy/webdriver/internal/ElementFactory.java

@@ -30,7 +30,5 @@
  * Translates from WebElement(s) to Darcy Elements.
  */
 public interface ElementFactory {
-    <T extends Element> T newElement(Class<T> type, Supplier<WebElement> sourceReference);
-    <T extends Element> List<T> newElementList(Class<T> type,
-            Supplier<List<WebElement>> sourceReference);
+    <T extends Element> T newElement(Class<T> type, WebElement sourceReference);
 }

src/main/java/com/redhat/darcy/webdriver/internal/TargetedElementFactory.java

@@ -48,18 +48,8 @@ public TargetedElementFactory(TargetedWebDriver driver, ElementConstructorMap el
     }
 
     @Override
-    public <T extends Element> T newElement(Class<T> type, Supplier<WebElement> sourceReference) {
-        return elementMap.get(type).newElement(
-                new TargetedWebElementSupplier(sourceReference, driver), this);
-    }
-
-    @Override
-    public <T extends Element> List<T> newElementList(Class<T> type,
-            Supplier<List<WebElement>> sourceReference) {
-        return new LazyList<T>(() -> sourceReference.get()
-                .stream()
-                .map(e -> newElement(type, () -> e))
-                .collect(Collectors.toList()));
+    public <T extends Element> T newElement(Class<T> type, WebElement source) {
+        return elementMap.get(type).newElement(source, this);
     }
 
 }

src/main/java/com/redhat/darcy/webdriver/internal/ThreadSafeCachingTargetedWebDriverFactory.java

@@ -0,0 +1,59 @@
+/*
+ Copyright 2014 Red Hat, Inc. and/or its affiliates.
+
+ This file is part of darcy-webdriver.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.redhat.darcy.webdriver.internal;
+
+import com.redhat.darcy.webdriver.internal.webdriver.ForwardingTargetedWebDriver;
+import com.redhat.darcy.webdriver.internal.webdriver.RefindingWebDriver;
+import com.redhat.darcy.webdriver.internal.webdriver.ThreadedTargetedWebDriver;
+
+import org.openqa.selenium.WebDriver;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class ThreadSafeCachingTargetedWebDriverFactory implements TargetedWebDriverFactory {
+    // It's important that all access to driver is gated by same executor
+    private final ExecutorService executor = Executors.newSingleThreadExecutor();
+    private final CachingTargetLocator cachingTargetLocator;
+
+    public ThreadSafeCachingTargetedWebDriverFactory(WebDriver untargetedDriver,
+            WebDriverTarget currentTarget) {
+        cachingTargetLocator = new CachingTargetLocator(currentTarget,
+                new RefindingWebDriver(untargetedDriver));
+    }
+
+    @Override
+    public TargetedWebDriver getTargetedWebDriver(WebDriverTarget target) {
+        // Order is important here: we want atomic operations to be executed in a single threaded
+        // queue, so driver switching needs to happen in the same queued task as the subsequent
+        // action. This means that the outer most driver should queue the operations of the
+        // forwarded driver -- which takes care of the switching.
+
+        // Inner to outer:
+        // 1. Refinding -- finds elements that can refind themselves if stale (these show up because
+        //    CachingTargetLocator is powered by a RefindingDriver).
+        // 2. Targeted -- targets a specific driver before proceeding, creates elements that do same
+        //    (So with refinding, creates elements that target a driver, then can refind themselves
+        //    if stale).
+        // 3. Threaded -- Assures atomic, single threaded interaction with driver from any source
+        return new ThreadedTargetedWebDriver(
+                new ForwardingTargetedWebDriver(cachingTargetLocator, target), executor);
+    }
+}