/*
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.pgm;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Vector;
  
  /**
   * List of all commands known by jgit's command line tools.
   * <p>
   * Commands are implementations of {@link TextBuiltin}, with an optional
   * {@link Command} class annotation to insert additional documentation or
   * override the default command name (which is guessed from the class name).
   * <p>
   * Commands may be registered by adding them to a services file in the same JAR
   * (or classes directory) as the command implementation. The service file name
   * is <code>META-INF/services/org.eclipse.jgit.pgm.TextBuiltin</code> and it
   * contains one concrete implementation class name per line.
   * <p>
   * Command registration is identical to Java 6's services, however the catalog
   * uses a lightweight wrapper to delay creating a command instance as much as
   * possible. This avoids initializing the AWT or SWT GUI toolkits even if the
   * command's constructor might require them.
   */
  public class CommandCatalog {
  	private static final CommandCatalog INSTANCE = new CommandCatalog();
  
  	/**
  	 * Locate a single command by its user friendly name.
  	 *
  	 * @param name
  	 *            name of the command. Typically in dash-lower-case-form, which
  	 *            was derived from the DashLowerCaseForm class name.
  	 * @return the command instance; null if no command exists by that name.
  	 */
  	public static CommandRef get(final String name) {
  		return INSTANCE.commands.get(name);
  	}
  
  	/**
  	 * @return all known commands, sorted by command name.
  	 */
  	public static CommandRef[] all() {
  		return toSortedArray(INSTANCE.commands.values());
  	}
  
  	/**
 	 * @return all common commands, sorted by command name.
 	 */
 	public static CommandRef[] common() {
 		final ArrayList<CommandRef> common = new ArrayList<CommandRef>();
 		for (final CommandRef c : INSTANCE.commands.values())
 			if (c.isCommon())
 				common.add(c);
 		return toSortedArray(common);
 	}
 
 	private static CommandRef[] toSortedArray(final Collection<CommandRef> c) {
 		final CommandRef[] r = c.toArray(new CommandRef[c.size()]);
 		Arrays.sort(r, new Comparator<CommandRef>() {
 			public int compare(final CommandRef o1, final CommandRef o2) {
 				return o1.getName().compareTo(o2.getName());
 			}
 		});
 		return r;
 	}
 
 	private final ClassLoader ldr;
 
 	private final Map<String, CommandRef> commands;
 
 	private CommandCatalog() {
 		ldr = Thread.currentThread().getContextClassLoader();
 		commands = new HashMap<String, CommandRef>();
 
 		final Enumeration<URL> catalogs = catalogs();
 		while (catalogs.hasMoreElements())
 			scan(catalogs.nextElement());
 	}
 
 	private Enumeration<URL> catalogs() {
 		try {
 			final String pfx = "META-INF/services/"; //$NON-NLS-1$
 			return ldr.getResources(pfx + TextBuiltin.class.getName());
 		} catch (IOException err) {
 			return new Vector<URL>().elements();
 		}
 	}
 
 	private void scan(final URL cUrl) {
 		final BufferedReader cIn;
 		try {
 			final InputStream in = cUrl.openStream();
 			cIn = new BufferedReader(new InputStreamReader(in, "UTF-8")); //$NON-NLS-1$
 		} catch (IOException err) {
 			// If we cannot read from the service list, go to the next.
 			//
 			return;
 		}
 
 		try {
 			String line;
 			while ((line = cIn.readLine()) != null) {
 				if (line.length() > 0 && !line.startsWith("#")) //$NON-NLS-1$
 					load(line);
 			}
 		} catch (IOException err) {
 			// If we failed during a read, ignore the error.
 			//
 		} finally {
 			try {
 				cIn.close();
 			} catch (IOException e) {
 				// Ignore the close error; we are only reading.
 			}
 		}
 	}
 
 	private void load(final String cn) {
 		final Class<? extends TextBuiltin> clazz;
 		try {
 			clazz = Class.forName(cn, false, ldr).asSubclass(TextBuiltin.class);
 		} catch (ClassNotFoundException notBuiltin) {
 			// Doesn't exist, even though the service entry is present.
 			//
 			return;
 		} catch (ClassCastException notBuiltin) {
 			// Isn't really a builtin, even though its listed as such.
 			//
 			return;
 		}
 
 		final CommandRef cr;
 		final Command a = clazz.getAnnotation(Command.class);
 		if (a != null)
 			cr = new CommandRef(clazz, a);
 		else
 			cr = new CommandRef(clazz);
 
 		commands.put(cr.getName(), cr);
 	}
 }