/*******************************************************************************
 * Copyright (C) 2016, Thomas Wolf <thomas.wolf@paranor.ch>
 *
 * 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
 *******************************************************************************/
package org.eclipse.egit.ui.internal;

import java.util.LinkedHashMap;

import org.eclipse.egit.ui.Activator;
import org.eclipse.jface.dialogs.IDialogSettings;
import org.eclipse.jgit.annotations.NonNull;

/**
 * Internal cache of known host names read from the plugin's
 * {@link IDialogSettings}. To be accessed only in the UI thread. The plugin
 * should store back the values in its
 * {@link Activator#stop(org.osgi.framework.BundleContext)} method by calling
 * {@link #store()}.
 */
public final class KnownHosts {

	private static final String KNOWN_HOSTS_KEY = "EGit.KnownHosts"; //$NON-NLS-1$

	private static final String[] DEFAULT_HOSTS = { "git.eclipse.org", //$NON-NLS-1$
			"github.com", "bitbucket.org" }; //$NON-NLS-1$ //$NON-NLS-2$

	private static HostStore knownHosts;

	private static boolean modified;

	private KnownHosts() {
		// Utility class shall not be instatiated.
	}

	/**
	 * Determines whether the given host name is known already.
	 *
	 * @param hostName
	 *            to check
	 * @return {@code true} is the host name is known, {@code false} otherwise.
	 */
	public static boolean isKnownHost(String hostName) {
		return hostName != null && getKnownHosts().containsKey(hostName);
	}

	/**
	 * Adds a new host name to the cache on known hosts.
	 *
	 * @param hostName
	 *            to add
	 */
	public static void addKnownHost(@NonNull String hostName) {
		getKnownHosts().put(hostName, null);
		modified = true; // At least the access order has changed
	}

	/**
	 * Stores back the known host names into the plugin's
	 * {@link IDialogSettings} if they were changed.
	 */
	public static void store() {
		if (modified) {
			String[] values = new String[knownHosts.size()];
			Activator.getDefault().getDialogSettings().put(KNOWN_HOSTS_KEY,
					knownHosts.keySet().toArray(values));
			modified = false;
		}
	}

	private static HostStore getKnownHosts() {
		if (knownHosts == null) {
			IDialogSettings settings = Activator.getDefault()
					.getDialogSettings();
			String[] values = settings.getArray(KNOWN_HOSTS_KEY);
			if (values == null) {
				settings.put(KNOWN_HOSTS_KEY, DEFAULT_HOSTS);
				values = DEFAULT_HOSTS;
			}
			knownHosts = new HostStore(values.length);
			for (int i = values.length - 1; i >= 0; i--) {
				String host = values[i];
				if (host != null && !host.isEmpty()) {
					knownHosts.put(host, null);
				}
			}
		}
		return knownHosts;
	}

	@SuppressWarnings("serial")
	private static class HostStore extends LinkedHashMap<String, String> {

		private static final int MAXIMUM_SIZE = 200;

		public HostStore(int size) {
			super(size < 10 ? 10 : size, 0.75f, true);
		}

		@Override
		protected boolean removeEldestEntry(
				java.util.Map.Entry<String, String> eldest) {
			return size() > MAXIMUM_SIZE;
		}
	}

}