/*
 * Copyright (C) 2008, Google Inc.
 * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2006-2008, 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.lib;

import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.util.MutableInteger;

/** Misc. constants used throughout JGit. */
public final class Constants {
	/** Hash function used natively by Git for all objects. */
	private static final String HASH_FUNCTION = "SHA-1";

	/**
	 * A Git object hash is 160 bits, i.e. 20 bytes.
	 * <p>
	 * Changing this assumption is not going to be as easy as changing this
	 * declaration.
	 */
	public static final int OBJECT_ID_LENGTH = 20;

	/**
	 * A Git object can be expressed as a 40 character string of hexadecimal
	 * digits.
	 *
	 * @see #OBJECT_ID_LENGTH
	 */
	public static final int OBJECT_ID_STRING_LENGTH = OBJECT_ID_LENGTH * 2;

	/** Special name for the "HEAD" symbolic-ref. */
	public static final String HEAD = "HEAD";

	/**
	 * Text string that identifies an object as a commit.
	 * <p>
	 * Commits connect trees into a string of project histories, where each
	 * commit is an assertion that the best way to continue is to use this other
	 * tree (set of files).
	 */
	public static final String TYPE_COMMIT = "commit";

	/**
	 * Text string that identifies an object as a blob.
	 * <p>
	 * Blobs store whole file revisions. They are used for any user file, as
	 * well as for symlinks. Blobs form the bulk of any project's storage space.
	 */
	public static final String TYPE_BLOB = "blob";

	/**
	 * Text string that identifies an object as a tree.
	 * <p>
	 * Trees attach object ids (hashes) to names and file modes. The normal use
	 * for a tree is to store a version of a directory and its contents.
	 */
	public static final String TYPE_TREE = "tree";

	/**
	 * Text string that identifies an object as an annotated tag.
	 * <p>
	 * Annotated tags store a pointer to any other object, and an additional
	 * message. It is most commonly used to record a stable release of the
	 * project.
	 */
	public static final String TYPE_TAG = "tag";

	private static final byte[] ENCODED_TYPE_COMMIT = encodeASCII(TYPE_COMMIT);

	private static final byte[] ENCODED_TYPE_BLOB = encodeASCII(TYPE_BLOB);

	private static final byte[] ENCODED_TYPE_TREE = encodeASCII(TYPE_TREE);

	private static final byte[] ENCODED_TYPE_TAG = encodeASCII(TYPE_TAG);

	/** An unknown or invalid object type code. */
	public static final int OBJ_BAD = -1;

	/**
	 * In-pack object type: extended types.
	 * <p>
	 * This header code is reserved for future expansion. It is currently
	 * undefined/unsupported.
	 */
	public static final int OBJ_EXT = 0;

	/**
	 * In-pack object type: commit.
	 * <p>
	 * Indicates the associated object is a commit.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 *
	 * @see #TYPE_COMMIT
	 */
	public static final int OBJ_COMMIT = 1;

	/**
	 * In-pack object type: tree.
	 * <p>
	 * Indicates the associated object is a tree.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 *
	 * @see #TYPE_BLOB
	 */
	public static final int OBJ_TREE = 2;

	/**
	 * In-pack object type: blob.
	 * <p>
	 * Indicates the associated object is a blob.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 *
	 * @see #TYPE_BLOB
	 */
	public static final int OBJ_BLOB = 3;

	/**
	 * In-pack object type: annotated tag.
	 * <p>
	 * Indicates the associated object is an annotated tag.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 *
	 * @see #TYPE_TAG
	 */
	public static final int OBJ_TAG = 4;

	/** In-pack object type: reserved for future use. */
	public static final int OBJ_TYPE_5 = 5;

	/**
	 * In-pack object type: offset delta
	 * <p>
	 * Objects stored with this type actually have a different type which must
	 * be obtained from their delta base object. Delta objects store only the
	 * changes needed to apply to the base object in order to recover the
	 * original object.
	 * <p>
	 * An offset delta uses a negative offset from the start of this object to
	 * refer to its delta base. The base object must exist in this packfile
	 * (even in the case of a thin pack).
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 */
	public static final int OBJ_OFS_DELTA = 6;

	/**
	 * In-pack object type: reference delta
	 * <p>
	 * Objects stored with this type actually have a different type which must
	 * be obtained from their delta base object. Delta objects store only the
	 * changes needed to apply to the base object in order to recover the
	 * original object.
	 * <p>
	 * A reference delta uses a full object id (hash) to reference the delta
	 * base. The base object is allowed to be omitted from the packfile, but
	 * only in the case of a thin pack being transferred over the network.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 */
	public static final int OBJ_REF_DELTA = 7;

	/**
	 * Pack file signature that occurs at file header - identifies file as Git
	 * packfile formatted.
	 * <p>
	 * <b>This constant is fixed and is defined by the Git packfile format.</b>
	 */
	public static final byte[] PACK_SIGNATURE = { 'P', 'A', 'C', 'K' };

	/** Native character encoding for commit messages, file names... */
	public static final String CHARACTER_ENCODING = "UTF-8";

	/** Native character encoding for commit messages, file names... */
	public static final Charset CHARSET;

	/** Default main branch name */
	public static final String MASTER = "master";

	/** Prefix for branch refs */
	public static final String R_HEADS = "refs/heads/";

	/** Prefix for remotes refs */
	public static final String R_REMOTES = "refs/remotes/";

	/** Prefix for tag refs */
	public static final String R_TAGS = "refs/tags/";

	/** Prefix for any ref */
	public static final String R_REFS = "refs/";

	/** Logs folder name */
	public static final String LOGS = "logs";

	/** Info refs folder */
	public static final String INFO_REFS = "info/refs";

	/** Packed refs file */
	public static final String PACKED_REFS = "packed-refs";

	/** The environment variable that contains the system user name */
	public static final String OS_USER_NAME_KEY = "user.name";

	/** The environment variable that contains the author's name */
	public static final String GIT_AUTHOR_NAME_KEY = "GIT_AUTHOR_NAME";

	/** The environment variable that contains the author's email */
	public static final String GIT_AUTHOR_EMAIL_KEY = "GIT_AUTHOR_EMAIL";

	/** The environment variable that contains the commiter's name */
	public static final String GIT_COMMITTER_NAME_KEY = "GIT_COMMITTER_NAME";

	/** The environment variable that contains the commiter's email */
	public static final String GIT_COMMITTER_EMAIL_KEY = "GIT_COMMITTER_EMAIL";

	/**
	 * The environment variable that limits how close to the root of the file
	 * systems JGit will traverse when looking for a repository root.
	 */
	public static final String GIT_CEILING_DIRECTORIES_KEY = "GIT_CEILING_DIRECTORIES";

	/**
	 * The environment variable that tells us which directory is the ".git"
	 * directory
	 */
	public static final String GIT_DIR_KEY = "GIT_DIR";

	/**
	 * The environment variable that tells us which directory is the working
	 * directory.
	 */
	public static final String GIT_WORK_TREE_KEY = "GIT_WORK_TREE";

	/**
	 * The environment variable that tells us which file holds the Git index.
	 */
	public static final String GIT_INDEX_KEY = "GIT_INDEX";

	/**
	 * The environment variable that tells us where objects are stored
	 */
	public static final String GIT_OBJECT_DIRECTORY_KEY = "GIT_OBJECT_DIRECTORY";

	/**
	 * The environment variable that tells us where to look for objects, besides
	 * the default objects directory.
	 */
	public static final String GIT_ALTERNATE_OBJECT_DIRECTORIES_KEY = "GIT_ALTERNATE_OBJECT_DIRECTORIES";

	/** Default value for the user name if no other information is available */
	public static final String UNKNOWN_USER_DEFAULT = "unknown-user";

	/** Beginning of the common "Signed-off-by: " commit message line */
	public static final String SIGNED_OFF_BY_TAG = "Signed-off-by: ";

	/** A gitignore file name */
	public static final String GITIGNORE_FILENAME = ".gitignore";

	/** Default remote name used by clone, push and fetch operations */
	public static final String DEFAULT_REMOTE_NAME = "origin";

	/** Default name for the Git repository directory */
	public static final String DOT_GIT = ".git";

	/** A bare repository typically ends with this string */
	public static final String DOT_GIT_EXT = ".git";

	/**
	 * Create a new digest function for objects.
	 *
	 * @return a new digest object.
	 * @throws RuntimeException
	 *             this Java virtual machine does not support the required hash
	 *             function. Very unlikely given that JGit uses a hash function
	 *             that is in the Java reference specification.
	 */
	public static MessageDigest newMessageDigest() {
		try {
			return MessageDigest.getInstance(HASH_FUNCTION);
		} catch (NoSuchAlgorithmException nsae) {
			throw new RuntimeException("Required hash function "
					+ HASH_FUNCTION + " not available.", nsae);
		}
	}

	/**
	 * Convert an OBJ_* type constant to a TYPE_* type constant.
	 *
	 * @param typeCode the type code, from a pack representation.
	 * @return the canonical string name of this type.
	 */
	public static String typeString(final int typeCode) {
		switch (typeCode) {
		case OBJ_COMMIT:
			return TYPE_COMMIT;
		case OBJ_TREE:
			return TYPE_TREE;
		case OBJ_BLOB:
			return TYPE_BLOB;
		case OBJ_TAG:
			return TYPE_TAG;
		default:
			throw new IllegalArgumentException("Bad object type: " + typeCode);
		}
	}

	/**
	 * Convert an OBJ_* type constant to an ASCII encoded string constant.
	 * <p>
	 * The ASCII encoded string is often the canonical representation of
	 * the type within a loose object header, or within a tag header.
	 *
	 * @param typeCode the type code, from a pack representation.
	 * @return the canonical ASCII encoded name of this type.
	 */
	public static byte[] encodedTypeString(final int typeCode) {
		switch (typeCode) {
		case OBJ_COMMIT:
			return ENCODED_TYPE_COMMIT;
		case OBJ_TREE:
			return ENCODED_TYPE_TREE;
		case OBJ_BLOB:
			return ENCODED_TYPE_BLOB;
		case OBJ_TAG:
			return ENCODED_TYPE_TAG;
		default:
			throw new IllegalArgumentException("Bad object type: " + typeCode);
		}
	}

	/**
	 * Parse an encoded type string into a type constant.
	 *
	 * @param id
	 *            object id this type string came from; may be null if that is
	 *            not known at the time the parse is occurring.
	 * @param typeString
	 *            string version of the type code.
	 * @param endMark
	 *            character immediately following the type string. Usually ' '
	 *            (space) or '\n' (line feed).
	 * @param offset
	 *            position within <code>typeString</code> where the parse
	 *            should start. Updated with the new position (just past
	 *            <code>endMark</code> when the parse is successful.
	 * @return a type code constant (one of {@link #OBJ_BLOB},
	 *         {@link #OBJ_COMMIT}, {@link #OBJ_TAG}, {@link #OBJ_TREE}.
	 * @throws CorruptObjectException
	 *             there is no valid type identified by <code>typeString</code>.
	 */
	public static int decodeTypeString(final AnyObjectId id,
			final byte[] typeString, final byte endMark,
			final MutableInteger offset) throws CorruptObjectException {
		try {
			int position = offset.value;
			switch (typeString[position]) {
			case 'b':
				if (typeString[position + 1] != 'l'
						|| typeString[position + 2] != 'o'
						|| typeString[position + 3] != 'b'
						|| typeString[position + 4] != endMark)
					throw new CorruptObjectException(id, "invalid type");
				offset.value = position + 5;
				return Constants.OBJ_BLOB;

			case 'c':
				if (typeString[position + 1] != 'o'
						|| typeString[position + 2] != 'm'
						|| typeString[position + 3] != 'm'
						|| typeString[position + 4] != 'i'
						|| typeString[position + 5] != 't'
						|| typeString[position + 6] != endMark)
					throw new CorruptObjectException(id, "invalid type");
				offset.value = position + 7;
				return Constants.OBJ_COMMIT;

			case 't':
				switch (typeString[position + 1]) {
				case 'a':
					if (typeString[position + 2] != 'g'
							|| typeString[position + 3] != endMark)
						throw new CorruptObjectException(id, "invalid type");
					offset.value = position + 4;
					return Constants.OBJ_TAG;

				case 'r':
					if (typeString[position + 2] != 'e'
							|| typeString[position + 3] != 'e'
							|| typeString[position + 4] != endMark)
						throw new CorruptObjectException(id, "invalid type");
					offset.value = position + 5;
					return Constants.OBJ_TREE;

				default:
					throw new CorruptObjectException(id, "invalid type");
				}

			default:
				throw new CorruptObjectException(id, "invalid type");
			}
		} catch (ArrayIndexOutOfBoundsException bad) {
			throw new CorruptObjectException(id, "invalid type");
		}
	}

	/**
	 * Convert an integer into its decimal representation.
	 *
	 * @param s
	 *            the integer to convert.
	 * @return a decimal representation of the input integer. The returned array
	 *         is the smallest array that will hold the value.
	 */
	public static byte[] encodeASCII(final long s) {
		return encodeASCII(Long.toString(s));
	}

	/**
	 * Convert a string to US-ASCII encoding.
	 *
	 * @param s
	 *            the string to convert. Must not contain any characters over
	 *            127 (outside of 7-bit ASCII).
	 * @return a byte array of the same length as the input string, holding the
	 *         same characters, in the same order.
	 * @throws IllegalArgumentException
	 *             the input string contains one or more characters outside of
	 *             the 7-bit ASCII character space.
	 */
	public static byte[] encodeASCII(final String s) {
		final byte[] r = new byte[s.length()];
		for (int k = r.length - 1; k >= 0; k--) {
			final char c = s.charAt(k);
			if (c > 127)
				throw new IllegalArgumentException("Not ASCII string: " + s);
			r[k] = (byte) c;
		}
		return r;
	}

	/**
	 * Convert a string to a byte array in the standard character encoding.
	 *
	 * @param str
	 *            the string to convert. May contain any Unicode characters.
	 * @return a byte array representing the requested string, encoded using the
	 *         default character encoding (UTF-8).
	 * @see #CHARACTER_ENCODING
	 */
	public static byte[] encode(final String str) {
		final ByteBuffer bb = Constants.CHARSET.encode(str);
		final int len = bb.limit();
		if (bb.hasArray() && bb.arrayOffset() == 0) {
			final byte[] arr = bb.array();
			if (arr.length == len)
				return arr;
		}

		final byte[] arr = new byte[len];
		bb.get(arr);
		return arr;
	}

	static {
		if (OBJECT_ID_LENGTH != newMessageDigest().getDigestLength())
			throw new LinkageError("Incorrect OBJECT_ID_LENGTH.");
		CHARSET = Charset.forName(CHARACTER_ENCODING);
	}

	private Constants() {
		// Hide the default constructor
	}
}