/*
    * Copyright (C) 2015, Matthias Sohn <matthias.sohn@sap.com>
    * 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,
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   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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  package org.eclipse.jgit.lfs.lib;
  
  import java.io.Serializable;
  import java.text.MessageFormat;
  
  import org.eclipse.jgit.lfs.errors.InvalidLongObjectIdException;
  import org.eclipse.jgit.lfs.internal.LfsText;
  import org.eclipse.jgit.lib.AbbreviatedObjectId;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.util.NB;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * A prefix abbreviation of an {@link LongObjectId}.
   * <p>
   * Enable abbreviating SHA-256 strings used by Git LFS, using sufficient leading
   * digits from the LongObjectId 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.
   *
   * Ported to SHA-256 from {@link AbbreviatedObjectId}
   *
   * @since 4.3
   */
  public final class AbbreviatedLongObjectId 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.LONG_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 AbbreviatedLongObjectId fromString(final byte[] buf,
 			final int offset, final int end) {
 		if (end - offset > Constants.LONG_OBJECT_ID_STRING_LENGTH)
 			throw new IllegalArgumentException(MessageFormat.format(
 							LfsText.get().invalidLongIdLength,
 					Integer.valueOf(end - offset),
 					Integer.valueOf(Constants.LONG_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 AbbreviatedLongObjectId fromLongObjectId(
 			AnyLongObjectId id) {
 		return new AbbreviatedLongObjectId(
 				Constants.LONG_OBJECT_ID_STRING_LENGTH, id.w1, id.w2, id.w3,
 				id.w4);
 	}
 
 	/**
 	 * Convert an AbbreviatedLongObjectId from hex characters.
 	 *
 	 * @param str
 	 *            the string to read from. Must be &lt;= 64 characters.
 	 * @return the converted object id.
 	 */
 	public static final AbbreviatedLongObjectId fromString(final String str) {
 		if (str.length() > Constants.LONG_OBJECT_ID_STRING_LENGTH)
 			throw new IllegalArgumentException(
 					MessageFormat.format(LfsText.get().invalidLongId, str));
 		final byte[] b = org.eclipse.jgit.lib.Constants.encodeASCII(str);
 		return fromHexString(b, 0, b.length);
 	}
 
 	private static final AbbreviatedLongObjectId fromHexString(final byte[] bs,
 			int ptr, final int end) {
 		try {
 			final long a = hexUInt64(bs, ptr, end);
 			final long b = hexUInt64(bs, ptr + 16, end);
 			final long c = hexUInt64(bs, ptr + 32, end);
 			final long d = hexUInt64(bs, ptr + 48, end);
 			return new AbbreviatedLongObjectId(end - ptr, a, b, c, d);
 		} catch (ArrayIndexOutOfBoundsException e1) {
 			throw new InvalidLongObjectIdException(bs, ptr, end - ptr);
 		}
 	}
 
 	private static final long hexUInt64(final byte[] bs, int p, final int end) {
 		if (16 <= end - p)
 			return RawParseUtils.parseHexInt64(bs, p);
 
 		long r = 0;
 		int n = 0;
 		while (n < 16 && p < end) {
 			r <<= 4;
 			r |= RawParseUtils.parseHexInt4(bs[p++]);
 			n++;
 		}
 		return r << (16 - n) * 4;
 	}
 
 	static long mask(final int nibbles, final long word, final long v) {
 		final long b = (word - 1) * 16;
 		if (b + 16 <= 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 long s = 64 - (nibbles - b) * 4;
 		return (v >>> s) << s;
 	}
 
 	/** Number of half-bytes used by this id. */
 	final int nibbles;
 
 	final long w1;
 
 	final long w2;
 
 	final long w3;
 
 	final long w4;
 
 	AbbreviatedLongObjectId(final int n, final long new_1, final long new_2,
 			final long new_3, final long new_4) {
 		nibbles = n;
 		w1 = new_1;
 		w2 = new_2;
 		w3 = new_3;
 		w4 = new_4;
 	}
 
 	/** @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.LONG_OBJECT_ID_STRING_LENGTH;
 	}
 
 	/** @return a complete ObjectId; null if {@link #isComplete()} is false */
 	public LongObjectId toLongObjectId() {
 		return isComplete() ? new LongObjectId(w1, w2, w3, w4) : 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 AnyLongObjectId other) {
 		int cmp;
 
 		cmp = NB.compareUInt64(w1, mask(1, other.w1));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w2, mask(2, other.w2));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w3, mask(3, other.w3));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt64(w4, mask(4, other.w4));
 	}
 
 	/**
 	 * Compare this abbreviation to a network-byte-order LongObjectId.
 	 *
 	 * @param bs
 	 *            array containing the other LongObjectId in network byte order.
 	 * @param p
 	 *            position within {@code bs} to start the compare at. At least
 	 *            32 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.compareUInt64(w1, mask(1, NB.decodeInt64(bs, p)));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w2, mask(2, NB.decodeInt64(bs, p + 8)));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w3, mask(3, NB.decodeInt64(bs, p + 16)));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt64(w4, mask(4, NB.decodeInt64(bs, p + 24)));
 	}
 
 	/**
 	 * Compare this abbreviation to a network-byte-order LongObjectId.
 	 *
 	 * @param bs
 	 *            array containing the other LongObjectId in network byte order.
 	 * @param p
 	 *            position within {@code bs} to start the compare at. At least 4
 	 *            longs, 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 long[] bs, final int p) {
 		int cmp;
 
 		cmp = NB.compareUInt64(w1, mask(1, bs[p]));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w2, mask(2, bs[p + 1]));
 		if (cmp != 0)
 			return cmp;
 
 		cmp = NB.compareUInt64(w3, mask(3, bs[p + 2]));
 		if (cmp != 0)
 			return cmp;
 
 		return NB.compareUInt64(w4, mask(4, bs[p + 3]));
 	}
 
 	/** @return value for a fan-out style map, only valid of length &gt;= 2. */
 	public final int getFirstByte() {
 		return (int) (w1 >>> 56);
 	}
 
 	private long mask(final long word, final long v) {
 		return mask(nibbles, word, v);
 	}
 
 	@Override
 	public int hashCode() {
 		return (int) (w1 >> 32);
 	}
 
 	@Override
 	public boolean equals(final Object o) {
 		if (o instanceof AbbreviatedLongObjectId) {
 			final AbbreviatedLongObjectId b = (AbbreviatedLongObjectId) o;
 			return nibbles == b.nibbles && w1 == b.w1 && w2 == b.w2
 					&& w3 == b.w3 && w4 == b.w4;
 		}
 		return false;
 	}
 
 	/**
 	 * @return string form of the abbreviation, in lower case hexadecimal.
 	 */
 	public final String name() {
 		final char[] b = new char[Constants.LONG_OBJECT_ID_STRING_LENGTH];
 
 		AnyLongObjectId.formatHexChar(b, 0, w1);
 		if (nibbles <= 16)
 			return new String(b, 0, nibbles);
 
 		AnyLongObjectId.formatHexChar(b, 16, w2);
 		if (nibbles <= 32)
 			return new String(b, 0, nibbles);
 
 		AnyLongObjectId.formatHexChar(b, 32, w3);
 		if (nibbles <= 48)
 			return new String(b, 0, nibbles);
 
 		AnyLongObjectId.formatHexChar(b, 48, w4);
 		return new String(b, 0, nibbles);
 	}
 
 	@SuppressWarnings("nls")
 	@Override
 	public String toString() {
 		return "AbbreviatedLongObjectId[" + name() + "]"; //$NON-NLS-1$
 	}
 }