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/*
 * Copyright (c) CQSE GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.conqat.engine.index.shared;

import java.util.regex.Pattern;

/**
 * Utility methods for working with Git refs.
 */
public class GitRefUtils {

	/**
	 * The Git ref name for the HEAD ref. Note that it's very important to distinguish the meaning of
	 * this ref for different kinds of Git repositories when determining the default branch (i.e. branch
	 * checked out upon cloning the repository).

	 * 

	 * For a regular local Git clone, which doesn't use the {@code --bare} or {@code --mirror} command
	 * line flags, the HEAD ref points to the revision of the currently checked out branch, tag or
	 * specific revision.

	 * 

	 * For a Git checkout with the command line flags {@code --bare} or {@code --mirror} the HEAD points
	 * to the revision of the default branch. 

	 * 

	 * If refs are loaded from a remote Git using the JGit LsRemoteCommand the (remote) HEAD points to
	 * the revision of the default branch.

	 * 

	 * However, for any of the different kinds of Git repositories there may be multiple branch head
	 * refs, pointing to the same revision as the HEAD ref. Hence the ref for the default branch isn't
	 * always uniquely defined and there may be multiple options for choosing it for a Git
	 * repository.

	 * 

	 * There exists a Git capability (see
	 * StackOverFlow,
	 * Official
	 * Github Release Notes) for determining the branch head ref to which the remote HEAD also
	 * points. However JGit doesn't support this capability and we're currently limited to guessing the
	 * default branch names.
	 */
	public static final String HEAD_REF_NAME = "HEAD";

	/** Prefix for the ref name for Git branch heads. */
	public static final String BRANCH_HEAD_REF_PREFIX = "refs/heads/";

	/** Prefix for refs to remote branches */
	public static final String REFERENCE_REMOTES_PREFIX = "refs/remotes/origin/";

	/** Name of the master branch. */
	public static final String MASTER_BRANCH = "master";

	/** Pattern for a SHA-1 hash which identifies a Git commit uniquely. */
	private static final Pattern COMMIT_HASH_PATTERN = Pattern.compile("^[\\da-f]{40}$");

	/** Base name for anonymous branches. */
	private static final String ANONYMOUS_BRANCH_NAME = "_anonymous_";

	/**
	 * Returns whether the given revision is a valid commit hash or the HEAD ref.
	 *
	 * @see #HEAD_REF_NAME
	 */
	public static boolean isCommitHashOrHeadRef(String revision) {
		return revision.equals(HEAD_REF_NAME) || COMMIT_HASH_PATTERN.matcher(revision).matches();
	}

	/**
	 * Returns true, if and only if the branch name starts with the {@link #ANONYMOUS_BRANCH_NAME}.
	 */
	public static boolean isAnonymousBranchName(String branchName) {
		return branchName != null && branchName.startsWith(ANONYMOUS_BRANCH_NAME);
	}

	/** Creates the name of a ref for a branch name. */
	public static String createBranchHeadRefName(String branchName) {
		return BRANCH_HEAD_REF_PREFIX + branchName;
	}

	/** Creates an anonymous branch name based on the given commit hash. */
	public static String createAnonymousBranchName(String commitHash) {
		return ANONYMOUS_BRANCH_NAME + commitHash;
	}
}