NavigationHistory.java

package nl.siegmann.epublib.browsersupport;

import java.util.ArrayList;
import java.util.List;

import nl.siegmann.epublib.domain.Book;
import nl.siegmann.epublib.domain.Resource;



/**
 * A history of the user's locations with the epub.
 * 
 * @author paul.siegmann
 *
 */
public class NavigationHistory implements NavigationEventListener {

	public static final int DEFAULT_MAX_HISTORY_SIZE = 1000;
	private static final long DEFAULT_HISTORY_WAIT_TIME = 1000;
	
	private static class Location {
		private String href;

		public Location(String href) {
			super();
			this.href = href;
		}

		@SuppressWarnings("unused")
		public void setHref(String href) {
			this.href = href;
		}

		public String getHref() {
			return href;
		}
	}
	
	private long lastUpdateTime = 0;
	private List<Location> locations = new ArrayList<>();
	private Navigator navigator;
	private int currentPos = -1;
	private int currentSize = 0;
	private int maxHistorySize = DEFAULT_MAX_HISTORY_SIZE;
	private long historyWaitTime = DEFAULT_HISTORY_WAIT_TIME;

	public NavigationHistory(Navigator navigator) {
		this.navigator = navigator;
		navigator.addNavigationEventListener(this);
		initBook(navigator.getBook());
	}
	
	public int getCurrentPos() {
		return currentPos;
	}


	public int getCurrentSize() {
		return currentSize;
	}
	
	public void initBook(Book book) {
		if (book == null) {
			return;
		}
		locations = new ArrayList<>();
		currentPos = -1;
		currentSize = 0;
		if (navigator.getCurrentResource() != null) {
			addLocation(navigator.getCurrentResource().getHref());
		}
	}
	
	/**
	 * If the time between a navigation event is less than the historyWaitTime then the new location is not added to the history. 
	 * When a user is rapidly viewing many pages using the slider we do not want all of them to be added to the history.
	 * 
	 * @return
	 */
	public long getHistoryWaitTime() {
		return historyWaitTime;
	}

	public void setHistoryWaitTime(long historyWaitTime) {
		this.historyWaitTime = historyWaitTime;
	}

	public void addLocation(Resource resource) {
		if (resource == null) {
			return;
		}
		addLocation(resource.getHref());
	}
	
	/**
	 * Adds the location after the current position.
	 * If the currentposition is not the end of the list then the elements between the current element and the end of the list will be discarded.
	 * Does nothing if the new location matches the current location.
	 * <br/>
	 * If this nr of locations becomes larger then the historySize then the first item(s) will be removed.
	 * 
	 * @param location
	 * @return
	 */
	public void addLocation(Location location) {
		// do nothing if the new location matches the current location
		if ( !(locations.isEmpty()) && 
				location.getHref().equals(locations.get(currentPos).getHref())) {
			return;
		}
		currentPos++;
		if (currentPos != currentSize) {
			locations.set(currentPos, location);
		} else {
			locations.add(location);
			checkHistorySize();
		}
		currentSize = currentPos + 1;
	}
	
	/**
	 * Removes all elements that are too much for the maxHistorySize out of the history.
	 * 
	 */
	private void checkHistorySize() {
		while(locations.size() > maxHistorySize) {
			locations.remove(0);
			currentSize--;
			currentPos--;
		}
	}

	public void addLocation(String href) {
		addLocation(new Location(href));
	}

	private String getLocationHref(int pos) {
		if (pos < 0 || pos >= locations.size()) {
			return null;
		}
		return locations.get(currentPos).getHref();	
	}

	/**
	 * Moves the current positions delta positions.
	 * 
	 * move(-1) to go one position back in history.<br/>
	 * move(1) to go one position forward.<br/>
	 * 
	 * @param delta
	 * 
	 * @return Whether we actually moved. If the requested value is illegal it will return false, true otherwise.
	 */
	public boolean move(int delta) {
		if (((currentPos + delta) < 0)
		|| ((currentPos + delta) >= currentSize)) {
			return false;
		}
		currentPos += delta;
		navigator.gotoResource(getLocationHref(currentPos), this);
		return true;
	}
	
	
	/**
	 * If this is not the source of the navigationEvent then the addLocation will be called with the href of the currentResource in the navigationEvent.
	 */
	@Override
	public void navigationPerformed(NavigationEvent navigationEvent) {
		if (this == navigationEvent.getSource()) {
			return;
		}
		if (navigationEvent.getCurrentResource() == null) {
			return;
		}
		
		if ((System.currentTimeMillis() - this.lastUpdateTime) > historyWaitTime) {
			// if the user scrolled rapidly through the pages then the last page will not be added to the history. We fix that here:
			addLocation(navigationEvent.getOldResource());

			addLocation(navigationEvent.getCurrentResource().getHref());
		}
		lastUpdateTime = System.currentTimeMillis();
	}

	public String getCurrentHref() {
		if (currentPos < 0 || currentPos >= locations.size()) {
			return null;
		}
		return locations.get(currentPos).getHref();
	}

	public void setMaxHistorySize(int maxHistorySize) {
		this.maxHistorySize = maxHistorySize;
	}

	public int getMaxHistorySize() {
		return maxHistorySize;
	}
}