/*******************************************************************************
 * Copyright (c) 2000, 2018 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.text.templates;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

import org.osgi.service.prefs.BackingStoreException;

import org.eclipse.core.runtime.Assert;
import org.eclipse.core.runtime.preferences.IEclipsePreferences;
import org.eclipse.core.runtime.preferences.IEclipsePreferences.IPreferenceChangeListener;

import org.eclipse.jface.text.templates.Template;
import org.eclipse.jface.text.templates.TemplateException;

/**
 * A collection of templates. Clients may instantiate this class. In order to
 * load templates contributed using the <code>org.eclipse.ui.editors.templates</code>
 * extension point, use a <code>ContributionTemplateStore</code>.
 *
 * @since 3.7
 */
public class TemplateStoreCore {

	/** The stored templates. */
	private final List<TemplatePersistenceData> fTemplates= new ArrayList<>();
	/** The preference store. */
	private IEclipsePreferences fPreferenceStore;
	/**
	 * The key into <code>fPreferenceStore</code> the value of which holds custom templates
	 * encoded as XML.
	 */
	private String fKey;
	/**
	 * The context type registry, or <code>null</code> if all templates regardless
	 * of context type should be loaded.
	 */
	private ContextTypeRegistry fRegistry;
	/**
	 * Set to <code>true</code> if property change events should be ignored (e.g. during writing
	 * to the preference store).
	 *
	 * @since 3.2
	 */
	private boolean fIgnorePreferenceStoreChanges= false;
	/**
	 * The property listener, if any is registered, <code>null</code> otherwise.
	 *
	 * @since 3.2
	 */
	private IPreferenceChangeListener fPropertyListener;


	/**
	 * Creates a new template store.
	 *
	 * @param store the preference store in which to store custom templates
	 *        under <code>key</code>
	 * @param key the key into <code>store</code> where to store custom
	 *        templates
	 */
	public TemplateStoreCore(IEclipsePreferences store, String key) {
		Assert.isNotNull(key);
		fPreferenceStore= store;
		fKey= key;
	}

	/**
	 * Creates a new template store with a context type registry. Only templates
	 * that specify a context type contained in the registry will be loaded by
	 * this store if the registry is not <code>null</code>.
	 *
	 * @param registry a context type registry, or <code>null</code> if all
	 *        templates should be loaded
	 * @param store the preference store in which to store custom templates
	 *        under <code>key</code>
	 * @param key the key into <code>store</code> where to store custom
	 *        templates
	 */
	public TemplateStoreCore(ContextTypeRegistry registry, IEclipsePreferences store, String key) {
		this(store, key);
		fRegistry= registry;
	}

	/**
	 * Loads the templates from contributions and preferences.
	 *
	 * @throws IOException if loading fails.
	 */
	public void load() throws IOException {
		fTemplates.clear();
		loadContributedTemplates();
		loadCustomTemplates();
	}

	/**
	 * Starts listening for property changes on the preference store. If the configured preference
	 * key changes, the template store is {@link #load() reloaded}. Call
	 * {@link #stopListeningForPreferenceChanges()} to remove any listener and stop the
	 * auto-updating behavior.
	 *
	 * @since 3.2
	 */
	public void startListeningForPreferenceChanges() {
		if (fPropertyListener == null) {
			fPropertyListener= event -> {
				/*
				 * Don't load if we are in the process of saving ourselves. We are in sync anyway after the
				 * save operation, and clients may trigger reloading by listening to preference store
				 * updates.
				 */
				if (!fIgnorePreferenceStoreChanges && fKey.equals(event.getKey()))
					try {
						load();
					} catch (IOException x) {
						handleException(x);
					}
			};
			fPreferenceStore.addPreferenceChangeListener(fPropertyListener);
		}

	}

	/**
	 * Stops the auto-updating behavior started by calling
	 * {@link #startListeningForPreferenceChanges()}.
	 *
	 * @since 3.2
	 */
	public void stopListeningForPreferenceChanges() {
		if (fPropertyListener != null) {
			fPreferenceStore.removePreferenceChangeListener(fPropertyListener);
			fPropertyListener= null;
		}
	}

	/**
	 * Handles an {@link IOException} thrown during reloading the preferences due to a preference
	 * store update. The default is to write to stderr.
	 *
	 * @param x the exception
	 * @since 3.2
	 */
	protected void handleException(IOException x) {
		x.printStackTrace();
	}

	/**
	 * Hook method to load contributed templates. Contributed templates are superseded
	 * by customized versions of user added templates stored in the preferences.
	 * <p>
	 * The default implementation does nothing.</p>
	 *
	 * @throws IOException if loading fails
	 */
	protected void loadContributedTemplates() throws IOException {
	}

	/**
	 * Adds a template to the internal store. The added templates must have
	 * a unique id.
	 *
	 * @param data the template data to add
	 */
	protected void internalAdd(TemplatePersistenceData data) {
		if (!data.isCustom()) {
			// check if the added template is not a duplicate id
			String id= data.getId();
			for (TemplatePersistenceData persistenceData : fTemplates) {
				if (persistenceData.getId() != null && persistenceData.getId().equals(id))
					return;
			}
			fTemplates.add(data);
		}
	}

	/**
	 * Saves the templates to the preferences.
	 *
	 * @throws IOException if the templates cannot be written
	 */
	public void save() throws IOException {
		ArrayList<TemplatePersistenceData> custom= new ArrayList<>();
		for (TemplatePersistenceData data : fTemplates) {
			if (data.isCustom() && !(data.isUserAdded() && data.isDeleted())) // don't save deleted user-added templates
				custom.add(data);
		}

		StringWriter output= new StringWriter();
		TemplateReaderWriter writer= new TemplateReaderWriter();
		writer.save(custom.toArray(new TemplatePersistenceData[custom.size()]), output);

		fIgnorePreferenceStoreChanges= true;
		try {
			fPreferenceStore.put(fKey, output.toString());
			fPreferenceStore.flush();
		} catch (BackingStoreException e) {
		} finally {
			fIgnorePreferenceStoreChanges= false;
		}
	}

	/**
	 * Adds a template encapsulated in its persistent form.
	 *
	 * @param data the template to add
	 */
	public void add(TemplatePersistenceData data) {

		if (!validateTemplate(data.getTemplate()))
			return;

		if (data.isUserAdded()) {
			fTemplates.add(data);
		} else {
			for (TemplatePersistenceData persistenceData : fTemplates) {
				if (persistenceData.getId() != null && persistenceData.getId().equals(data.getId())) {
					persistenceData.setTemplate(data.getTemplate());
					persistenceData.setDeleted(data.isDeleted());
					persistenceData.setEnabled(data.isEnabled());
					return;
				}
			}

			// add an id which is not contributed as add-on
			if (data.getTemplate() != null) {
				TemplatePersistenceData newData= new TemplatePersistenceData(data.getTemplate(), data.isEnabled(), data.getId());
				fTemplates.add(newData);
			}
		}
	}

	/**
	 * Removes a template from the store.
	 *
	 * @param data the template to remove
	 */
	public void delete(TemplatePersistenceData data) {
		if (data.isUserAdded())
			fTemplates.remove(data);
		else
			data.setDeleted(true);
	}

	/**
	 * Restores all contributed templates that have been deleted.
	 */
	public void restoreDeleted() {
		for (TemplatePersistenceData data : fTemplates) {
			if (data.isDeleted())
				data.setDeleted(false);
		}
	}

	/**
	 * Deletes all user-added templates and reverts all contributed templates.
	 *
	 * @param doSave <code>true</code> if the store should be saved after restoring
	 * @since 3.5
	 */
	public void restoreDefaults(boolean doSave) {
		String oldValue= null;
		if (!doSave)
			oldValue= fPreferenceStore.get(fKey, null);

		try {
			fIgnorePreferenceStoreChanges= true;
			// See IPreferenceStore for default String value
			fPreferenceStore.put(fKey, ""); //$NON-NLS-1$
		} finally {
			fIgnorePreferenceStoreChanges= false;
		}

		try {
			load();
		} catch (IOException x) {
			// can't log from jface-text
			handleException(x);
		}

		if (oldValue != null) {
			try {
				fIgnorePreferenceStoreChanges= true;
				fPreferenceStore.put(fKey, oldValue);
			} finally {
				fIgnorePreferenceStoreChanges= false;
			}
		}
	}

	/**
	 * Deletes all user-added templates and reverts all contributed templates.
	 * <p>
	 * <strong>Note:</strong> the store will be saved after restoring.
	 * </p>
	 */
	public void restoreDefaults() {
		restoreDefaults(true);
	}

	/**
	 * Returns all enabled templates.
	 *
	 * @return all enabled templates
	 */
	public Template[] getTemplates() {
		return getTemplates(null);
	}

	/**
	 * Returns all enabled templates for the given context type.
	 *
	 * @param contextTypeId the id of the context type of the requested templates, or <code>null</code> if all templates should be returned
	 * @return all enabled templates for the given context type
	 */
	public Template[] getTemplates(String contextTypeId) {
		List<Template> templates= new ArrayList<>();
		for (TemplatePersistenceData data : fTemplates) {
			if (data.isEnabled() && !data.isDeleted() && (contextTypeId == null || contextTypeId.equals(data.getTemplate().getContextTypeId())))
				templates.add(data.getTemplate());
		}

		return templates.toArray(new Template[templates.size()]);
	}

	/**
	 * Returns the first enabled template that matches the name.
	 *
	 * @param name the name of the template searched for
	 * @return the first enabled template that matches both name and context type id, or <code>null</code> if none is found
	 */
	public Template findTemplate(String name) {
		return findTemplate(name, null);
	}

	/**
	 * Returns the first enabled template that matches both name and context type id.
	 *
	 * @param name the name of the template searched for
	 * @param contextTypeId the context type id to clip unwanted templates, or <code>null</code> if any context type is OK
	 * @return the first enabled template that matches both name and context type id, or <code>null</code> if none is found
	 */
	public Template findTemplate(String name, String contextTypeId) {
		Assert.isNotNull(name);

		for (TemplatePersistenceData data : fTemplates) {
			Template template= data.getTemplate();
			if (data.isEnabled() && !data.isDeleted()
					&& (contextTypeId == null || contextTypeId.equals(template.getContextTypeId()))
					&& name.equals(template.getName()))
				return template;
		}

		return null;
	}

	/**
	 * Returns the first enabled template that matches the given template id.
	 *
	 * @param id the id of the template searched for
	 * @return the first enabled template that matches id, or <code>null</code> if none is found
	 * @since 3.1
	 */
	public Template findTemplateById(String id) {
		TemplatePersistenceData data= getTemplateData(id);
		if (data != null && !data.isDeleted())
			return data.getTemplate();

		return null;
	}

	/**
	 * Returns all template data.
	 *
	 * @param includeDeleted whether to include deleted data
	 * @return all template data, whether enabled or not
	 */
	public TemplatePersistenceData[] getTemplateData(boolean includeDeleted) {
		List<TemplatePersistenceData> datas= new ArrayList<>();
		for (TemplatePersistenceData data : fTemplates) {
			if (includeDeleted || !data.isDeleted())
				datas.add(data);
		}

		return datas.toArray(new TemplatePersistenceData[datas.size()]);
	}

	/**
	 * Returns the template data of the template with id <code>id</code> or
	 * <code>null</code> if no such template can be found.
	 *
	 * @param id the id of the template data
	 * @return the template data of the template with id <code>id</code> or <code>null</code>
	 * @since 3.1
	 */
	public TemplatePersistenceData getTemplateData(String id) {
		Assert.isNotNull(id);
		for (TemplatePersistenceData data : fTemplates) {
			if (id.equals(data.getId()))
				return data;
		}

		return null;
	}

	private void loadCustomTemplates() throws IOException {
		String pref= fPreferenceStore.get(fKey, null);
		if (pref != null && !pref.trim().isEmpty()) {
			Reader input= new StringReader(pref);
			TemplateReaderWriter reader= new TemplateReaderWriter();
			TemplatePersistenceData[] datas= reader.read(input);
			for (TemplatePersistenceData data : datas) {
				add(data);
			}
		}
	}

	/**
	 * Validates a template against the context type registered in the context
	 * type registry. Returns always <code>true</code> if no registry is
	 * present.
	 *
	 * @param template the template to validate
	 * @return <code>true</code> if validation is successful or no context
	 *         type registry is specified, <code>false</code> if validation
	 *         fails
	 */
	private boolean validateTemplate(Template template) {
		String contextTypeId= template.getContextTypeId();
		if (contextExists(contextTypeId)) {
			if (fRegistry != null)
				try {
					fRegistry.getContextType(contextTypeId).validate(template.getPattern());
				} catch (TemplateException e) {
					return false;
				}
			return true;
		}

		return false;
	}

	/**
	 * Returns <code>true</code> if a context type id specifies a valid context type
	 * or if no context type registry is present.
	 *
	 * @param contextTypeId the context type id to look for
	 * @return <code>true</code> if the context type specified by the id
	 *         is present in the context type registry, or if no registry is
	 *         specified
	 */
	private boolean contextExists(String contextTypeId) {
		return contextTypeId != null && (fRegistry == null || fRegistry.getContextType(contextTypeId) != null);
	}

	/**
	 * Returns the registry.
	 *
	 * @return Returns the registry
	 */
	protected ContextTypeRegistry getRegistry() {
		return fRegistry;
	}

	/**
	 * Return the key into the Preference Store whose value contains
	 * the custom templates encoded as XML.
	 *
	 * @return the key in the Preference Store
	 */
	protected final String getKey () {
		return fKey;
	}

	/**
	 * Return the stored templates
	 * @return the stored templates
	 */
	protected final List<TemplatePersistenceData> internalGetTemplates () {
		return fTemplates;
	}

}

