package crisp.wbwiki.client;
   
   import com.google.gwt.user.client.rpc.AsyncCallback;
   
   public class ClientStateManager {
   	/** The last page version loaded from the server */
   	private Page lastLoadedPage = null;
   	private final WikiServiceAsync wikiService;
   	private static boolean loggingEnabled = true;
  	
  	
  	public ClientStateManager(final WikiServiceAsync wikiService) {
  		this.wikiService = wikiService;
  	}
  
  	public void synchronizeWithServer(final WikiGui gui) {
  		String currentContent = gui.getCurrentContent();
  		
  		final Integer lastLoadedVersion;
  		final String contentToSendToServer;
  		if (lastLoadedPage == null) {
  			lastLoadedVersion = null;
  			contentToSendToServer = null;
  		} else {
  			lastLoadedVersion = new Integer(lastLoadedPage.getVersion());
  			if (lastLoadedPage.getContent().equals(currentContent)) {
  				contentToSendToServer = null;
  			} else {
  				log(gui, "Content has changed!\nold: '" + lastLoadedPage.getContent() + "'\nnew: '" + currentContent + "'");
  				contentToSendToServer = currentContent;
  			}
  		}
  		log(gui, "Calling synchronize(" + lastLoadedVersion + ", " + contentToSendToServer + ")");
  		wikiService.synchronize(
  				lastLoadedVersion, 
  				contentToSendToServer, 
  				new AsyncCallback() {
  					public void onFailure(Throwable err) {
  						//TODO error handling
  						err.printStackTrace();
  					}
  					public void onSuccess(Object response) {
  						Page updatedPage = (Page) response;
  						log(gui, "Received response: " + updatedPage);
  						if (updatedPage == null) {
  							//The server didn't feel any need to give me an updated page							
  							if (contentToSendToServer == null) {
  								//I didn't send any content to the server,
  								//so nothing has changed by me or anybody else.
  								//So we do nothing.
  							} else {
  								//Nothing has changed on the server side,
  								//but I sent new content so the version number was updated.
  								lastLoadedPage = new Page(
  										lastLoadedPage.getVersion() + 1,
  										contentToSendToServer
  										);
  							}	
  						} else {
  							//I received an updated page from the server,
  							//so someone else has been changing the page!
  							//Need to update my state.
  							lastLoadedPage = updatedPage;
  							gui.setCurrentContent(updatedPage.getContent());
  						}
  					}			
  				}
  		);
  	}
  
  	void log(WikiGui gui, String logEntry) {
  		if (loggingEnabled) {
  			gui.log(logEntry);
  		}
  	}
  
  }