/*
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.pgm;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  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 org.eclipse.jgit.pgm.TextBuiltin},
   * with an optional {@link org.eclipse.jgit.pgm.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(String name) {
  		return INSTANCE.commands.get(name);
  	}
  
  	/**
  	 * Get all commands sorted by their name
  	 *
  	 * @return all known commands, sorted by command name.
  	 */
  	public static CommandRef[] all() {
  		return toSortedArray(INSTANCE.commands.values());
  	}
  
  	/**
  	 * Get all common commands sorted by their name
  	 *
  	 * @return all common commands, sorted by command name.
  	 */
  	public static CommandRef[] common() {
  		final ArrayList<CommandRef> common = new ArrayList<>();
  		for (CommandRef c : INSTANCE.commands.values())
  			if (c.isCommon())
  				common.add(c);
  		return toSortedArray(common);
  	}
  
  	private static CommandRef[] toSortedArray(Collection<CommandRef> c) {
  		final CommandRef[] r = c.toArray(new CommandRef[0]);
  		Arrays.sort(r, (CommandRef o1, CommandRef o2) -> 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<>();
  
  		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(URL cUrl) {
 		try (BufferedReader cIn = new BufferedReader(
 				new InputStreamReader(cUrl.openStream(), UTF_8))) {
 			String line;
 			while ((line = cIn.readLine()) != null) {
 				if (line.length() > 0 && !line.startsWith("#")) //$NON-NLS-1$
 					load(line);
 			}
 		} catch (IOException e) {
 			// Ignore errors
 		}
 	}
 
 	private void load(String cn) {
 		final Class<? extends TextBuiltin> clazz;
 		try {
 			clazz = Class.forName(cn, false, ldr).asSubclass(TextBuiltin.class);
 		} catch (ClassNotFoundException | ClassCastException notBuiltin) {
 			// Doesn't exist, even though the service entry is present.
 			// 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);
 	}
 }