package com.atlassian.webdriver.visualcomparison;
   
   import com.atlassian.selenium.visualcomparison.ScreenElement;
   import com.atlassian.selenium.visualcomparison.v2.BrowserEngine;
   import com.atlassian.selenium.visualcomparison.v2.settings.Resolution;
   import com.atlassian.webdriver.debug.WebDriverDebug;
   import org.openqa.selenium.*;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
  
  import javax.annotation.Nonnull;
  import javax.annotation.Nullable;
  import javax.inject.Inject;
  import java.io.File;
  import java.util.Collections;
  import java.util.List;
  
  import static com.atlassian.webdriver.utils.JavaScriptUtils.execute;
  import static com.google.common.base.Preconditions.checkNotNull;
  import static java.lang.String.format;
  
  /**
   * @since 2.3
   */
  public final class WebDriverBrowserEngine implements BrowserEngine
  {
      private static final Logger log = LoggerFactory.getLogger(WebDriverBrowserEngine.class);
  
      private final WebDriver webDriver;
  
      @Inject
      public WebDriverBrowserEngine(@Nonnull WebDriver webDriver)
      {
          this.webDriver = checkNotNull(webDriver, "webDriver");
      }
  
      @SuppressWarnings("ConstantConditions")
      @Nonnull
      @Override
      public ScreenElement getElementAt(int x, int y)
      {
          try
          {
              ElementByPoint elementByPoint = new ElementByPoint(x, y).calculate();
              // scroll to put the element in viewport
              executeScript(Object.class, format("window.scrollTo(%d,%d)",
                      elementByPoint.scrollTo.getX(), elementByPoint.scrollTo.getY()));
              final WebElement element = webDriver.findElement(byPoint(elementByPoint.elementCoordinates));
              return new SimpleScreenElement(executeScript(String.class,
                      "var d = document.createElement('div'); d.appendChild(arguments[0].cloneNode(true)); return d.innerHTML;",
                      element));
          }
          catch (Exception e)
          {
              log.error(format("Error while getting screen element at %d,%d", x, y), e);
              return new SimpleScreenElement("");
          }
      }
  
      @Nonnull
      @Override
      public BrowserEngine resizeTo(@Nonnull Resolution resolution)
      {
          setSize(resolution);
          // NOT a mistake... WebDriver sometimes needs an extra kick in butt
          setSize(resolution);
          return this;
      }
  
      @Nonnull
      @Override
      public BrowserEngine captureScreenshotTo(@Nonnull File file)
      {
          new WebDriverDebug(webDriver).takeScreenshotTo(file);
          return this;
      }
  
      @Nonnull
      @Override
      public BrowserEngine reloadPage()
      {
          webDriver.navigate().refresh();
          return this;
      }
  
      @Nullable
      @Override
      public <T> T executeScript(@Nonnull Class<T> returnType, @Nonnull String script, @Nonnull Object... args)
      {
          return execute(returnType, script, webDriver, args);
      }
  
      private By byPoint(final Point coordinates)
      {
          return new By()
          {
              @Override
              public List<WebElement> findElements(SearchContext context)
              {
                 final String findByPoint = format("return document.elementFromPoint(%d,%d);", coordinates.getX(),
                         coordinates.getY());
                 final WebElement element = execute(WebElement.class, findByPoint, webDriver);
                 return element != null ? Collections.singletonList(element) : Collections.<WebElement>emptyList();
             }
 
             @Override
             public String toString()
             {
                 return format("By point in viewport %d,%d", coordinates.getX(), coordinates.getY());
             }
         };
     }
 
     @SuppressWarnings("ConstantConditions")
     private Dimension getDimensionFor(String selector)
     {
         long x = executeScript(Long.class, "return jQuery(" + selector + ").width();");
         long y = executeScript(Long.class, "return jQuery(" + selector + ").height();");
         return new Dimension((int) x, (int) y);
     }
 
     private void setSize(Resolution resolution)
     {
         webDriver.manage().window().setSize(new Dimension(resolution.getWidth(), resolution.getHeight()));
     }
 
     private final class ElementByPoint
     {
         private final int x;
         private final int y;
 
         private Dimension viewport;
         private Dimension document;
 
         Point scrollTo;
         Point elementCoordinates;
 
         private ElementByPoint(int x, int y)
         {
             this.x = x;
             this.y = y;
         }
 
         ElementByPoint calculate()
         {
             this.document = getDimensionFor("document");
             this.viewport = getDimensionFor("window");
             calculateScroll();
             calculateCoordinates();
             return this;
         }
 
         private void calculateScroll()
         {
             int deltaX = Math.max(0, document.getWidth() - viewport.getWidth());
             int scrollX = Math.min(x, deltaX);
             int deltaY = Math.max(0, document.getHeight() - viewport.getHeight());
             int scrollY = Math.min(y, deltaY);
             scrollTo = new Point(scrollX, scrollY);
         }
 
         private void calculateCoordinates()
         {
             int relativeX = x - scrollTo.getX();
             int relativeY = y - scrollTo.getY();
             elementCoordinates = new Point(relativeX, relativeY);
         }
     }
 
     private static final class SimpleScreenElement implements ScreenElement
     {
 
         private final String html;
 
         private SimpleScreenElement(@Nonnull String html)
         {
             this.html = html;
         }
 
         @Override
         @Nonnull
         public String getHtml()
         {
             return html;
         }
     }
 
 }