/*
    * Copyright (C) 2018, Google LLC. 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.internal.transport.parser;
  
  import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;
  
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Set;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.errors.PackProtocolException;
  import org.eclipse.jgit.internal.JGitText;
  
  /**
   * In the pack negotiation phase (protocol v0/v1), the client sends a list of
   * wants. The first "want" line is special, as it (can) have a list of
   * capabilities appended.
   *
   * E.g. "want oid cap1 cap2 cap3"
   *
   * Do not confuse this line with the first one in the reference advertisement,
   * which is sent by the server, looks like
   * "b8f7c471373b8583ced0025cfad8c9916c484b76 HEAD\0 cap1 cap2 cap3" and is
   * parsed by the BasePackConnection.readAdvertisedRefs method.
   *
   * This class parses the input want line and holds the results: the actual want
   * line and the capabilities.
   *
   */
  public class FirstWant {
  	private final String line;
  
  	private final Set<String> capabilities;
  
  	@Nullable
  	private final String agent;
  
  	private static final String AGENT_PREFIX = OPTION_AGENT + '=';
  
  	/**
  	 * Parse the first want line in the protocol v0/v1 pack negotiation.
  	 *
  	 * @param line
  	 *            line from the client.
  	 * @return an instance of FirstWant
  	 * @throws PackProtocolException
  	 *             if the line doesn't follow the protocol format.
  	 */
  	public static FirstWant fromLine(String line) throws PackProtocolException {
  		String wantLine;
  		Set<String> capabilities;
  		String agent = null;
  
  		if (line.length() > 45) {
  			String opt = line.substring(45);
  			if (!opt.startsWith(" ")) { //$NON-NLS-1$
  				throw new PackProtocolException(JGitText.get().wantNoSpaceWithCapabilities);
  			}
  			opt = opt.substring(1);
  
  			HashSet<String> opts = new HashSet<>();
  			for (String clientCapability : opt.split(" ")) { //$NON-NLS-1$
  				if (clientCapability.startsWith(AGENT_PREFIX)) {
  					agent = clientCapability.substring(AGENT_PREFIX.length());
  				} else {
  					opts.add(clientCapability);
  				}
  			}
  			wantLine = line.substring(0, 45);
  			capabilities = Collections.unmodifiableSet(opts);
  		} else {
  			wantLine = line;
  			capabilities = Collections.emptySet();
  		}
  
  		return new FirstWant(wantLine, capabilities, agent);
  	}
  
  	private FirstWant(String line, Set<String> capabilities,
  			@Nullable String agent) {
  		this.line = line;
  		this.capabilities = capabilities;
  		this.agent = agent;
  	}
  
  	/** @return non-capabilities part of the line. */
  	public String getLine() {
  		return line;
  	}
  
  	/**
 	 * @return capabilities parsed from the line as an immutable set (excluding
 	 *         agent).
 	 */
 	public Set<String> getCapabilities() {
 		return capabilities;
 	}
 
 	/** @return client user agent parsed from the line. */
 	@Nullable
 	public String getAgent() {
 		return agent;
 	}
 }