// Copyright (C) 2009 The Android Open Source Project
//
// 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 com.google.gerrit.server;

import com.google.gerrit.client.reviewdb.Change;
import com.google.gerrit.client.reviewdb.ReviewDb;
import com.google.gwtorm.client.OrmException;

import org.spearce.jgit.util.Base64;
import org.spearce.jgit.util.NB;

public class ChangeUtil {
  private static int uuidPrefix;
  private static int uuidSeq;

  /**
   * Generate a new unique identifier for change message entities.
   *
   * @param db the database connection, used to increment the change message
   *        allocation sequence.
   * @return the new unique identifier.
   * @throws OrmException the database couldn't be incremented.
   */
  public static String messageUUID(final ReviewDb db) throws OrmException {
    final byte[] raw = new byte[8];
    fill(raw, db);
    return Base64.encodeBytes(raw);
  }

  private static synchronized void fill(byte[] raw, ReviewDb db)
      throws OrmException {
    if (uuidSeq == 0) {
      uuidPrefix = db.nextChangeMessageId();
      uuidSeq = Integer.MAX_VALUE;
    }
    NB.encodeInt32(raw, 0, uuidPrefix);
    NB.encodeInt32(raw, 4, uuidSeq--);
  }

  public static void updated(final Change c) {
    c.resetLastUpdatedOn();
    computeSortKey(c);
  }

  public static void computeSortKey(final Change c) {
    // The encoding uses minutes since Wed Oct 1 00:00:00 2008 UTC.
    // We overrun approximately 4,085 years later, so ~6093.
    //
    final long lastUpdatedOn =
        (c.getLastUpdatedOn().getTime() / 1000L) - 1222819200L;
    final StringBuilder r = new StringBuilder(16);
    r.setLength(16);
    formatHexInt(r, 0, (int) (lastUpdatedOn / 60));
    formatHexInt(r, 8, c.getId().get());
    c.setSortKey(r.toString());
  }

  private static final char[] hexchar =
      {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', //
          'a', 'b', 'c', 'd', 'e', 'f'};

  private static void formatHexInt(final StringBuilder dst, final int p, int w) {
    int o = p + 7;
    while (o >= p && w != 0) {
      dst.setCharAt(o--, hexchar[w & 0xf]);
      w >>>= 4;
    }
    while (o >= p) {
      dst.setCharAt(o--, '0');
    }
  }
}