/*
    * Copyright (C) 2008-2009, Google Inc.
    * 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
    *
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  package org.eclipse.jgit.lib;
  
  import java.io.Serializable;
  import java.text.MessageFormat;
  
  import org.eclipse.jgit.errors.InvalidObjectIdException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.util.NB;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * A prefix abbreviation of an {@link ObjectId}.
   * <p>
   * Sometimes Git produces abbreviated SHA-1 strings, using sufficient leading
   * digits from the ObjectId name to still be unique within the repository the
   * string was generated from. These ids are likely to be unique for a useful
   * period of time, especially if they contain at least 6-10 hex digits.
   * <p>
   * This class converts the hex string into a binary form, to make it more
   * efficient for matching against an object.
   */
  public final class AbbreviatedObjectId implements Serializable {
  	private static final long serialVersionUID = 1L;
  
  	/**
  	 * Test a string of characters to verify it is a hex format.
  	 * <p>
  	 * If true the string can be parsed with {@link #fromString(String)}.
  	 *
  	 * @param id
  	 *            the string to test.
  	 * @return true if the string can converted into an AbbreviatedObjectId.
  	 */
  	public static final boolean isId(final String id) {
  		if (id.length() < 2 || Constants.OBJECT_ID_STRING_LENGTH < id.length())
  			return false;
  		try {
  			for (int i = 0; i < id.length(); i++)
  				RawParseUtils.parseHexInt4((byte) id.charAt(i));
  			return true;
  		} catch (ArrayIndexOutOfBoundsException e) {
  			return false;
  		}
  	}
  
  	/**
  	 * Convert an AbbreviatedObjectId from hex characters (US-ASCII).
  	 *
  	 * @param buf
  	 *            the US-ASCII buffer to read from.
  	 * @param offset
  	 *            position to read the first character from.
  	 * @param end
  	 *            one past the last position to read (<code>end-offset</code> is
  	 *            the length of the string).
  	 * @return the converted object id.
 	 */
 	public static final AbbreviatedObjectId fromString(final byte[] buf,
 			final int offset, final int end) {
 		if (end - offset > Constants.OBJECT_ID_STRING_LENGTH)
 			throw new IllegalArgumentException(MessageFormat.format(
 					JGitText.get().invalidIdLength,
 					Integer.valueOf(end - offset),
 					Integer.valueOf(Constants.OBJECT_ID_STRING_LENGTH)));
 		return fromHexString(buf, offset, end);
 	}
 
 	/**
 	 * Convert an AbbreviatedObjectId from an {@link AnyObjectId}.
 	 * <p>
 	 * This method copies over all bits of the Id, and is therefore complete
 	 * (see {@link #isComplete()}).
 	 *
 	 * @param id
 	 *            the {@link ObjectId} to convert from.
 	 * @return the converted object id.
 	 */
 	public static final AbbreviatedObjectId fromObjectId(AnyObjectId id) {
 		return new AbbreviatedObjectId(Constants.OBJECT_ID_STRING_LENGTH,
 				id.w1, id.w2, id.w3, id.w4, id.w5);
 	}
 
 	/**
 	 * Convert an AbbreviatedObjectId from hex characters.
 	 *
 	 * @param str
 	 *            the string to read from. Must be &lt;= 40 characters.
 	 * @return the converted object id.
 	 */
 	public static final AbbreviatedObjectId fromString(final String str) {
 		if (str.length() > Constants.OBJECT_ID_STRING_LENGTH)
 			throw new IllegalArgumentException(MessageFormat.format(JGitText.get().invalidId, str));
 		final byte[] b = Constants.encodeASCII(str);
 		return fromHexString(b, 0, b.length);
 	}
 
 	private static final AbbreviatedObjectId fromHexString(final byte[] bs,
 			int ptr, final int end) {
 		try {
 			final int a = hexUInt32(bs, ptr, end);
 			final int b = hexUInt32(bs, ptr + 8, end);
 			final int c = hexUInt32(bs, ptr + 16, end);
 			final int d = hexUInt32(bs, ptr + 24, end);
 			final int e = hexUInt32(bs, ptr + 32, end);
 			return new AbbreviatedObjectId(end - ptr, a, b, c, d, e);
 		} catch (ArrayIndexOutOfBoundsException e1) {
 			throw new InvalidObjectIdException(bs, ptr, end - ptr);
 		}
 	}
 
 	private static final int hexUInt32(final byte[] bs, int p, final int end) {
 		if (8 <= end - p)
 			return RawParseUtils.parseHexInt32(bs, p);
 
 		int r = 0, n = 0;
 		while (n < 8 && p < end) {
 			r <<= 4;
 			r |= RawParseUtils.parseHexInt4(bs[p++]);
 			n++;
 		}
 		return r << (8 - n) * 4;
 	}
 
 	static int mask(final int nibbles, final int word, final int v) {
 		final int b = (word - 1) * 8;
 		if (b + 8 <= nibbles) {
 			// We have all of the bits required for this word.
 			//
 			return v;
 		}
 
 		if (nibbles <= b) {
 			// We have none of the bits required for this word.
 			//
 			return 0;
 		}
 
 		final int s = 32 - (nibbles - b) * 4;
 		return (v >>> s) << s;
 	}
 
 	/** Number of half-bytes used by this id. */
 	final int nibbles;
 
 	final int w1;
 
 	final int w2;
 
 	final int w3;
 
 	final int w4;
 
 	final int w5;
 
 	AbbreviatedObjectId(final int n, final int new_1, final int new_2,
 			final int new_3, final int new_4, final int new_5) {
 		nibbles = n;
 		w1 = new_1;
 		w2 = new_2;
 		w3 = new_3;
 		w4 = new_4;
 		w5 = new_5;
 	}
 
 	/** @return number of hex digits appearing in this id */
 	public int length() {
 		return nibbles;
 	}
 
 	/** @return true if this ObjectId is actually a complete id. */
 	public boolean isComplete() {
 		return length() == Constants.OBJECT_ID_STRING_LENGTH;
 	}
 
 	/** @return a complete ObjectId; null if {@link #isComplete()} is false */
 	public ObjectId toObjectId() {
 		return isComplete() ? new ObjectId(w1, w2, w3, w4, w5) : null;
 	}
 
 	/**
 	 * Compares this abbreviation to a full object id.
 	 *
 	 * @param other
 	 *            the other object id.
 	 * @return &lt;0 if this abbreviation names an object that is less than
 	 *         <code>other</code>; 0 if this abbreviation exactly matches the
 	 *         first {@link #length()} digits of <code>other.name()</code>;
 	 *         &gt;0 if this abbreviation names an object that is after
 	 *         <code>other</code>.
 	 */
 	public final int prefixCompare(final AnyObjectId other) {
 		int cmp;
 
 		cmp = NB.compareUInt32(w1, mask(1, other.w1));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w2, mask(2, other.w2));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w3, mask(3, other.w3));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w4, mask(4, other.w4));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt32(w5, mask(5, other.w5));
 	}
 
 	/**
 	 * Compare this abbreviation to a network-byte-order ObjectId.
 	 *
 	 * @param bs
 	 *            array containing the other ObjectId in network byte order.
 	 * @param p
 	 *            position within {@code bs} to start the compare at. At least
 	 *            20 bytes, starting at this position are required.
 	 * @return &lt;0 if this abbreviation names an object that is less than
 	 *         <code>other</code>; 0 if this abbreviation exactly matches the
 	 *         first {@link #length()} digits of <code>other.name()</code>;
 	 *         &gt;0 if this abbreviation names an object that is after
 	 *         <code>other</code>.
 	 */
 	public final int prefixCompare(final byte[] bs, final int p) {
 		int cmp;
 
 		cmp = NB.compareUInt32(w1, mask(1, NB.decodeInt32(bs, p)));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w2, mask(2, NB.decodeInt32(bs, p + 4)));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w3, mask(3, NB.decodeInt32(bs, p + 8)));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w4, mask(4, NB.decodeInt32(bs, p + 12)));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt32(w5, mask(5, NB.decodeInt32(bs, p + 16)));
 	}
 
 	/**
 	 * Compare this abbreviation to a network-byte-order ObjectId.
 	 *
 	 * @param bs
 	 *            array containing the other ObjectId in network byte order.
 	 * @param p
 	 *            position within {@code bs} to start the compare at. At least 5
 	 *            ints, starting at this position are required.
 	 * @return &lt;0 if this abbreviation names an object that is less than
 	 *         <code>other</code>; 0 if this abbreviation exactly matches the
 	 *         first {@link #length()} digits of <code>other.name()</code>;
 	 *         &gt;0 if this abbreviation names an object that is after
 	 *         <code>other</code>.
 	 */
 	public final int prefixCompare(final int[] bs, final int p) {
 		int cmp;
 
 		cmp = NB.compareUInt32(w1, mask(1, bs[p]));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w2, mask(2, bs[p + 1]));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w3, mask(3, bs[p + 2]));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt32(w4, mask(4, bs[p + 3]));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt32(w5, mask(5, bs[p + 4]));
 	}
 
 	/** @return value for a fan-out style map, only valid of length &gt;= 2. */
 	public final int getFirstByte() {
 		return w1 >>> 24;
 	}
 
 	private int mask(final int word, final int v) {
 		return mask(nibbles, word, v);
 	}
 
 	@Override
 	public int hashCode() {
 		return w1;
 	}
 
 	@Override
 	public boolean equals(final Object o) {
 		if (o instanceof AbbreviatedObjectId) {
 			final AbbreviatedObjectId b = (AbbreviatedObjectId) o;
 			return nibbles == b.nibbles && w1 == b.w1 && w2 == b.w2
 					&& w3 == b.w3 && w4 == b.w4 && w5 == b.w5;
 		}
 		return false;
 	}
 
 	/**
 	 * @return string form of the abbreviation, in lower case hexadecimal.
 	 */
 	public final String name() {
 		final char[] b = new char[Constants.OBJECT_ID_STRING_LENGTH];
 
 		AnyObjectId.formatHexChar(b, 0, w1);
 		if (nibbles <= 8)
 			return new String(b, 0, nibbles);
 
 		AnyObjectId.formatHexChar(b, 8, w2);
 		if (nibbles <= 16)
 			return new String(b, 0, nibbles);
 
 		AnyObjectId.formatHexChar(b, 16, w3);
 		if (nibbles <= 24)
 			return new String(b, 0, nibbles);
 
 		AnyObjectId.formatHexChar(b, 24, w4);
 		if (nibbles <= 32)
 			return new String(b, 0, nibbles);
 
 		AnyObjectId.formatHexChar(b, 32, w5);
 		return new String(b, 0, nibbles);
 	}
 
 	@SuppressWarnings("nls")
 	@Override
 	public String toString() {
 		return "AbbreviatedObjectId[" + name() + "]"; //$NON-NLS-1$
 	}
 }