/*******************************************************************************
 * Copyright (c) 2010 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.wst.sse.ui.internal.contentassist;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.eclipse.core.runtime.Assert;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.InvalidRegistryObjectException;
import org.eclipse.core.runtime.Platform;
import org.eclipse.core.runtime.Status;
import org.eclipse.core.runtime.content.IContentType;
import org.eclipse.jface.preference.IPreferenceStore;
import org.eclipse.wst.sse.ui.internal.Logger;
import org.eclipse.wst.sse.ui.internal.SSEUIPlugin;


/**
 * <p>A registry for all extensions to the
 * <code>org.eclipse.wst.sse.ui.completionProposal</code>
 * extension point.</p>
 */
public final class CompletionProposalComputerRegistry {

	/** The extension schema name of the extension point */
	private static final String EXTENSION_POINT = "completionProposal"; //$NON-NLS-1$
	
	/** The extension schema name of proposal category child elements. */
	private static final String ELEM_PROPOSAL_CATEGORY = "proposalCategory"; //$NON-NLS-1$
	
	/** The extension schema name of proposal computer child elements. */
	private static final String ELEM_PROPOSAL_COMPUTER = "proposalComputer"; //$NON-NLS-1$
	
	/** The extension schema name of proposal computer activation child elements. */
	private static final String ELEM_PROPOSAL_COMPUTER_EXTENDED_ACTIVATION = "proposalComputerExtendedActivation"; //$NON-NLS-1$
	
	/** The extension schema name for element ID attributes */
	private static final String ATTR_ID= "id"; //$NON-NLS-1$
	
	/** preference key to keep track of the last known number of content assist computers */
	private static final String NUM_COMPUTERS_PREF_KEY = "content_assist_number_of_computers"; //$NON-NLS-1$
	
	/**
	 * A fake partition type ID stating used to say a {@link CompletionProposalComputerDescriptor} should
	 * be associated with all partition types in a given content type.
	 */
	private static final String ALL_PARTITION_TYPES_ID = "all_partition_types_fake_ID"; //$NON-NLS-1$
	
	/** State where in the registry has not yet been loaded */
	private static final byte NONE = 0;

	/** State where the registry is being initialized */
	private static final byte INITIALIZING = 1;
	
	/** State where in the registry is currently being loaded */
	private static final byte LOADING = 2;
	
	/** State where in the registry has been loaded */
	private static final byte LOADED = 3;

	/** The singleton instance. */
	private static CompletionProposalComputerRegistry fgSingleton= null;

	/**
	 * @return the singleton instance of the registry
	 */
	public static synchronized CompletionProposalComputerRegistry getDefault() {
		if (fgSingleton == null) {
			fgSingleton= new CompletionProposalComputerRegistry();
		}

		return fgSingleton;
	}

	/**
	 * <code>{@link Map}&lt{@link String}, {@link CompletionProposalContentTypeContext}&gt</code>
	 * <ul>
	 * <li><b>key:</b> content type ID</li>
	 * <li><b>value:</b> the context for the associated content type ID</li>
	 * <ul>
	 */
	private final Map fActivationContexts;
	
	/**
	 * <code>{@link Map}&lt{@link String}, {@link CompletionProposalComputerDescriptor}&gt</code>
	 * <ul>
	 * <li><b>key:</b> descriptor ID</li>
	 * <li><b>value:</b> descriptor</li>
	 * <ul>
	 */
	private final Map fDescriptors = new HashMap();

	/** The {@link CompletionProposalCategory}s tracked by this registry */
	private final List fCategories = new ArrayList();
	
	/** Unmodifiable public list of the {@link CompletionProposalCategory}s tracked by this registry */
	private final List fPublicCategories = Collections.unmodifiableList(fCategories);
	
	/**
	 * <p>The current state of the registry</p>
	 * 
	 * @see #NONE
	 * @see #LOADING
	 * @see #LOADED
	 */
	private byte fState;
	
	/**
	 * Lock that is held while loading, operations waiting for
	 * load to finish can lock on this as well
	 */
	private final Object fLoadingLock;

	/** <code>true</code> if computers have been uninstalled since last load */
	private boolean fHasUninstalledComputers= false;

	/**
	 * Creates a new instance.
	 */
	private CompletionProposalComputerRegistry() {
		this.fActivationContexts = new HashMap();
		this.fState = CompletionProposalComputerRegistry.NONE;
		this.fLoadingLock = new Object();
	}
	
	/**
	 * <p>Calling this when the registry has not yet been loaded will start a
	 * {@link Thread} to start loading the registry.  All other operations on
	 * the registry will be blocked until the loading has completed.  If
	 * the registry has already been loaded or is loading then this
	 * method does nothing.</p>
	 */
	public synchronized void initialize() {
		if(fState == CompletionProposalComputerRegistry.NONE) {
			fState = CompletionProposalComputerRegistry.INITIALIZING;
			new Thread() {
				public void run() {
					CompletionProposalComputerRegistry.this.load();
				}
			}.start();
		}
	}
	
	/**
	 * <p><b>NOTE: </b>The returned list is read-only and is sorted in the order that the
	 * extensions were read in. There are no duplicate elements in the returned list.
	 * The returned list may change if plug-ins are loaded or unloaded while the
	 * application is running.</p>
	 *
	 * @return the list of proposal categories contributed to the
	 * <code>org.eclipse.wst.sse.ui.completionProposal</code> extension point (element type:
	 *         {@link CompletionProposalCategory})
	 */
	public List getProposalCategories() {
		internalEnsureLoaded();
		return fPublicCategories;
	}
	
	/**
	 * <p><b>NOTE: </b>The returned list is read-only and is sorted in the order that the
	 * extensions were read in. There are no duplicate elements in the returned list.
	 * The returned list may change if plug-ins are loaded or unloaded while the
	 * application is running.</p>
	 * 
	 * @param contentTypeID get the {@link CompletionProposalCategory}s associated with this ID
	 * @return the {@link CompletionProposalCategory}s associated with the given content type ID
	 */
	public List getProposalCategories(String contentTypeID) {
		internalEnsureLoaded();
		List result = new ArrayList();
		for(int i = 0; i < fCategories.size(); ++i) {
			CompletionProposalCategory category = ((CompletionProposalCategory)fCategories.get(i));
			if(category.hasComputers(contentTypeID)) {
				result.add(category);
			}
		}
		
		return Collections.unmodifiableList(result);
	}
	
	/**
	 * @return <code>true</code> if the registry detected that computers got uninstalled since the last run
	 * 			<code>false</code> otherwise or if {@link #resetUnistalledComputers()} has been called
	 */
	public boolean hasUninstalledComputers() {
		return fHasUninstalledComputers;
	}
	
	/**
	 * <p>Clears the setting that uninstalled computers have been detected.
	 * This setting is used to decide weather a helpful message should be
	 * displayed to the user</p>
	 */
	public void resetUnistalledComputers() {
		fHasUninstalledComputers = false;
	}
	
	/**
	 * <p>Adds the given {@link CompletionProposalComputerDescriptor} to the registry.</p>
	 * 
	 * @param contentTypeID the ID of the content type to associated the descriptor with
	 * @param partitionTypeID the ID of the partition type in the content type to associate
	 * the descriptor with, or <code>null</code> to associate with all partition types in
	 * the content type.
	 * @param descriptor the {@link CompletionProposalComputerDescriptor} to associate with
	 * the given content type and partition type
	 */
	void putDescription(String contentTypeID, String partitionTypeID,
			CompletionProposalComputerDescriptor descriptor) {
		
		if(partitionTypeID == null) {
			partitionTypeID = ALL_PARTITION_TYPES_ID;
		}
		
		CompletionProposalContentTypeContext context = getContext(contentTypeID);
		context.putDescriptor(partitionTypeID, descriptor);
	}

	/**
	 * @param contentTypeID get only descriptors associated with this content type
	 * @param partitionTypeID get only descriptors associated with this partition type as well
	 * as describers associated with any partition type in the given content type
	 * @return all of the {@link CompletionProposalComputerDescriptor}s associated with the
	 * given content type and partition type (including any describers associated with all
	 * partition types in the given content type)
	 */
	List getProposalComputerDescriptors(String contentTypeID, String partitionTypeID) {
		internalEnsureLoaded();
		
		Set descriptorsSet = new HashSet();
		List contexts = this.getContexts(contentTypeID);
		for(int i = 0; i < contexts.size(); ++i) {
			CompletionProposalContentTypeContext contentSpecificContext =
				(CompletionProposalContentTypeContext)contexts.get(i);
			
			//add all descriptors specific to the given content type and the given partition type
			descriptorsSet.addAll(contentSpecificContext.getDescriptors(partitionTypeID));
			
			//add all descriptors specific to the given content type but not specific to a partition type
			descriptorsSet.addAll(contentSpecificContext.getDescriptors(ALL_PARTITION_TYPES_ID));
		}
		
		List descriptors = new ArrayList(descriptorsSet);
		return descriptors != null ? Collections.unmodifiableList(descriptors) : Collections.EMPTY_LIST;
	}
	
	/**
	 * @param contentTypeID get only descriptors associated with this content type
	 * @return all of the {@link CompletionProposalComputerDescriptor}s associated with the
	 * given content type
	 */
	List getProposalComputerDescriptors(String contentTypeID) {
		internalEnsureLoaded();
		
		Set descriptorsSet = new HashSet();
		
		List contexts = this.getContexts(contentTypeID);
		for(int i = 0; i < contexts.size(); ++i) {
			CompletionProposalContentTypeContext contentSpecificContext =
				(CompletionProposalContentTypeContext)contexts.get(i);
			
			//add all descriptors specific to the given content type
			descriptorsSet.addAll(contentSpecificContext.getDescriptors());
		}
		
		List descriptors = new ArrayList(descriptorsSet);
		return descriptors != null ? Collections.unmodifiableList(descriptors) : Collections.EMPTY_LIST;
	}

	/**
	 * @return Unmodifiable list of all of the {@link CompletionProposalComputerDescriptor}s associated with
	 * this registry
	 */
	List getProposalComputerDescriptors() {
		internalEnsureLoaded();
		return Collections.unmodifiableList( new ArrayList(fDescriptors.values()));
	}

	/**
	 * <p>This method performs differently depending on the state of the registry</p>
	 * <ul>
	 * <li>{@link #NONE} - forces the registry to load now on the current thread</li>
	 * <li>{@link #LOADING} - blocks until the registry has finished loading on
	 * whichever thread it is being loaded on</li>
	 * <li>{@link #LOADED} - immediately returns</li>
	 * </ul>
	 */
	private void internalEnsureLoaded() {
		switch (fState) {
			case CompletionProposalComputerRegistry.NONE:
			case CompletionProposalComputerRegistry.INITIALIZING: {
				load();
				break;
			}
			case CompletionProposalComputerRegistry.LOADING: {
				//as soon as this lock is released the loading process is done
				synchronized (fLoadingLock) {
					//sanity check
					Assert.isTrue(fState == CompletionProposalComputerRegistry.LOADED,
							"The state of the registry should be guaranteed to be LOADED " + //$NON-NLS-1$
							" once the loading lock has been released."); //$NON-NLS-1$
				}
				break;
			}
		}
	}
	
	/**
	 * <p>Loads the completion proposal extension points if they
	 * have not been loaded already</p>
	 */
	private void load() {
		/* hold this lock while loading, others waiting for load to
		 * finish can synchronize on this lock to be guaranteed the load
		 * will be done when the lock is released
		 */
		synchronized (fLoadingLock) {
			if(fState == CompletionProposalComputerRegistry.NONE || fState == CompletionProposalComputerRegistry.INITIALIZING) {
				//update the state
				fState = CompletionProposalComputerRegistry.LOADING;
				
				IExtensionRegistry registry= Platform.getExtensionRegistry();
				List extensionElements= new ArrayList(Arrays.asList(registry.getConfigurationElementsFor(SSEUIPlugin.ID, EXTENSION_POINT)));
		
				Map loadedDescriptors = new HashMap();
				List extendedComputerActivations = new ArrayList();
		
				//get the categories and remove them from the extension elements
				List categories= getCategories(extensionElements);
				
				//deal with the proposal computers and set aside the proposal computer activation extensions
				for (Iterator iter= extensionElements.iterator(); iter.hasNext();) {
					IConfigurationElement element= (IConfigurationElement) iter.next();
					try {
						if (element.getName().equals(ELEM_PROPOSAL_COMPUTER)) {
							//create the descriptor and add it to the registry
							CompletionProposalComputerDescriptor desc = new CompletionProposalComputerDescriptor(element, categories);
							desc.addToRegistry();
							loadedDescriptors.put(desc.getId(), desc);
						} else if(element.getName().equals(ELEM_PROPOSAL_COMPUTER_EXTENDED_ACTIVATION)) {
							extendedComputerActivations.add(element);
						}
		
					} catch (InvalidRegistryObjectException x) {
						/*
						 * Element is not valid any longer as the contributing plug-in was unloaded or for
						 * some other reason. Do not include the extension in the list and log it
						 */
						String message = "The extension ''" + element.toString() + "'' is invalid."; //$NON-NLS-1$ //$NON-NLS-2$
						IStatus status= new Status(IStatus.WARNING, SSEUIPlugin.ID, IStatus.OK, message, x);
						Logger.log(status);
					} catch (CoreException x) {
						Logger.log(x.getStatus());
					}
				}
				
				//deal with extended computer activations
				for(int i = 0; i < extendedComputerActivations.size(); ++i) {
					IConfigurationElement element = (IConfigurationElement)extendedComputerActivations.get(i);
					String proposalComputerID = element.getAttribute(ATTR_ID);
					CompletionProposalComputerDescriptor descriptor =
						(CompletionProposalComputerDescriptor)loadedDescriptors.get(proposalComputerID);
					if(descriptor != null) {
						try {
							//add the extra activation contexts to the registry
							CompletionProposalComputerDescriptor.parseActivationAndAddToRegistry(element, descriptor);
						} catch (InvalidRegistryObjectException x) {
							/*
							 * Element is not valid any longer as the contributing plug-in was unloaded or for
							 * some other reason. Do not include the extension in the list and log it
							 */
							String message = "The extension ''" + element.toString() + "'' is invalid."; //$NON-NLS-1$ //$NON-NLS-2$
							IStatus status= new Status(IStatus.WARNING, SSEUIPlugin.ID, IStatus.OK, message, x);
							Logger.log(status);
						} catch (CoreException x) {
							Logger.log(x.getStatus());
						}
						
					} else {
						//activation extension has invalid computer ID
						Logger.log(Logger.WARNING, "Configuration element " + element + //$NON-NLS-1$
								" intented to extend an existing completion proposal computer" + //$NON-NLS-1$
								" specified an invalid completion proposal computer ID " + //$NON-NLS-1$
								proposalComputerID);
					}
				}
		
				fCategories.clear();
				fCategories.addAll(categories);
		
				fDescriptors.clear();
				fDescriptors.putAll(loadedDescriptors);
				
				updateUninstalledComputerCount();
				
				//update the state
				fState = CompletionProposalComputerRegistry.LOADED;
			}
		}
	}

	/**
	 * <p>Updates the uninstalled computer count</p>
	 */
	private void updateUninstalledComputerCount() {
		IPreferenceStore preferenceStore = SSEUIPlugin.getDefault().getPreferenceStore();
		int lastNumberOfComputers= preferenceStore.getInt(NUM_COMPUTERS_PREF_KEY);
		int currNumber= fDescriptors.size();
		fHasUninstalledComputers= lastNumberOfComputers > currNumber;
		preferenceStore.putValue(NUM_COMPUTERS_PREF_KEY, Integer.toString(currNumber));
	}

	/**
	 * <p>Configures the categories found in the given {@link IConfigurationElement}s
	 * and removes them from the given list.</p>
	 * 
	 * @param extensionElements {@link IConfigurationElement}s that include proposal
	 * category extensions
	 * @return {@link CompletionProposalCategory}s created from the given
	 * {@link IConfigurationElement}s that defined new proposal categories.
	 */
	private List getCategories(List extensionElements) {
		List categories= new ArrayList();
		for (Iterator iter= extensionElements.iterator(); iter.hasNext();) {
			IConfigurationElement element= (IConfigurationElement) iter.next();
			try {
				if (element.getName().equals(ELEM_PROPOSAL_CATEGORY)) {
					iter.remove(); // remove from list to leave only computers

					CompletionProposalCategory category= new CompletionProposalCategory(element);
					categories.add(category);
				}
			} catch (InvalidRegistryObjectException x) {
				/* Element is not valid any longer as the contributing plug-in was unloaded or for
				 * some other reason. Do not include the extension in the list and log it
				 */
				String message = "The extension ''" + element.toString() + "'' has become invalid."; //$NON-NLS-1$ //$NON-NLS-2$
				IStatus status= new Status(IStatus.WARNING, SSEUIPlugin.ID, IStatus.OK, message, x);
				Logger.log(status);
			} catch (CoreException x) {
				Logger.log(x.getStatus());
			}
		}
		
		return categories;
	}
	
	/**
	 * <p>Gets the {@link CompletionProposalContentTypeContext} associated with the given content type,
	 * if one does not already exist then one is created</p>
	 * 
	 * @param contentTypeID get the {@link CompletionProposalContentTypeContext} associated with this content type
	 * @return the existing or new {@link CompletionProposalContentTypeContext} associated with the given content type
	 */
	private CompletionProposalContentTypeContext getContext(String contentTypeID) {
		CompletionProposalContentTypeContext context = (CompletionProposalContentTypeContext)this.fActivationContexts.get(contentTypeID);
		if(context == null) {
			context = new CompletionProposalContentTypeContext(contentTypeID);
			this.fActivationContexts.put(contentTypeID, context);
		}
		
		return context;
	}
	
	/**
	 * <p>Gets all of the {@link CompletionProposalContentTypeContext}s associated with
	 * the given content type ID.  A context is considered associated if its associated content type ID
	 * is either the given content type ID or is a base content type ID of the given content type ID.</p>
	 * 
	 * @param contentTypeID get the contexts for this content type ID
	 * @return {@link List} of {@link CompletionProposalContentTypeContext}s associated with the given
	 * content type ID
	 */
	private List getContexts(String contentTypeID) {
		List contexts = new ArrayList();
		IContentType contentType = Platform.getContentTypeManager().getContentType(contentTypeID);
		
		while(contentType != null) {
			Object context = this.fActivationContexts.get(contentType.getId());
			if(context != null) {
				contexts.add(context);
			}
			
			contentType = contentType.getBaseType();
		}
		
		return contexts;
	}
}