package org.eclipse.jst.jsp.core.internal.taglib;


import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IProject;
import org.eclipse.jdt.core.ElementChangedEvent;
import org.eclipse.jdt.core.IElementChangedListener;
import org.eclipse.jdt.core.IJavaElement;
import org.eclipse.jdt.core.IJavaElementDelta;

/**
 * Manages creation and caching (ordered MRU) of TaglibHelpers.
 * Removes helpers when their classpath changes (so they are rebuilt).
 * There is one helper per project (with a specific classpath entry).
 * 
 * @author pavery
 */
public class TaglibHelperManager implements IElementChangedListener {
   

    private static TaglibHelperManager instance = null;
    // using a cache of just 3 loaders
    private TaglibHelperCache fCache = new TaglibHelperCache(3);

    private TaglibHelperManager() {
        // use instance
    }
    public static synchronized TaglibHelperManager getInstance() {
        if(instance == null)
            instance = new TaglibHelperManager();
        return instance;
    }
    
    public TaglibHelper getTaglibHelper(IFile f) {
        IProject p = f.getProject();
        return getHelperFromCache(p);
    }
    
    /**
     * @param projectPath
     */
    private TaglibHelper getHelperFromCache(IProject project) {
        return fCache.getHelper(project);
    }
    
    /**
     * Update classpath for appropriate loader.
     * @see org.eclipse.jdt.core.IElementChangedListener#elementChanged(org.eclipse.jdt.core.ElementChangedEvent)
     */
    public void elementChanged(ElementChangedEvent event) {

        // handle classpath changes
        IJavaElementDelta delta = event.getDelta();
        if(delta.getElement().getElementType() == IJavaElement.JAVA_MODEL) {
            IJavaElementDelta[] changed = delta.getChangedChildren();
            for (int i = 0; i < changed.length; i++) {
                if((changed[i].getFlags() & IJavaElementDelta.F_CLASSPATH_CHANGED) != 0) {
                    IJavaElement proj = changed[i].getElement();
                    handleClasspathChange(changed, i, proj);
                }
            }
        }
    }
    
    /**
     * @param changed
     * @param i
     * @param proj
     */
    private void handleClasspathChange(IJavaElementDelta[] changed, int i, IJavaElement proj) {

        if(proj.getElementType() == IJavaElement.JAVA_PROJECT) {
            String projectPath = proj.getPath().toString().replace('\\', '/');
            fCache.removeHelper(projectPath);
        }
    }
}