package net.jpountz.xxhash;

import java.util.zip.Checksum;
import java.io.Closeable;

/*
 * Copyright 2020 Adrien Grand and the lz4-java contributors.
 *
 * 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.
 */



/**
 * Streaming interface for {@link XXHash32}.
 * <p>
 * This API is compatible with the {@link XXHash32 block API} and the following
 * code samples are equivalent:
 * <pre class="prettyprint">
 *   int hash(XXHashFactory xxhashFactory, byte[] buf, int off, int len, int seed) {
 *     return xxhashFactory.hash32().hash(buf, off, len, seed);
 *   }
 * </pre>
 * <pre class="prettyprint">
 *   int hash(XXHashFactory xxhashFactory, byte[] buf, int off, int len, int seed) {
 *     StreamingXXHash32 sh32 = xxhashFactory.newStreamingHash32(seed);
 *     sh32.update(buf, off, len);
 *     return sh32.getValue();
 *   }
 * </pre>
 * <p>
 * Instances of this class are <b>not</b> thread-safe.
 */
public abstract class StreamingXXHash32 implements Closeable {

  interface Factory {

    StreamingXXHash32 newStreamingHash(int seed);

  }

  final int seed;

  StreamingXXHash32(int seed) {
    this.seed = seed;
  }

  /**
   * Returns the value of the checksum.
   *
   * @return the checksum
   */
  public abstract int getValue();

  /**
   * Updates the value of the hash with buf[off:off+len].
   *
   * @param buf the input data
   * @param off the start offset in buf
   * @param len the number of bytes to hash
   */
  public abstract void update(byte[] buf, int off, int len);

  /**
   * Resets this instance to the state it had right after instantiation. The
   * seed remains unchanged.
   */
  public abstract void reset();

  /**
   * Releases any system resources associated with this instance.
   * It is not mandatory to call this method after using this instance
   * because the system resources are released anyway when this instance
   * is reclaimed by GC.
   */
  @Override
  public void close() {
  }

  @Override
  public String toString() {
    return getClass().getSimpleName() + "(seed=" + seed + ")";
  }

  /**
   * Returns a {@link Checksum} view of this instance. Modifications to the view
   * will modify this instance too and vice-versa.
   *
   * @return the {@link Checksum} object representing this instance
   */
  public final Checksum asChecksum() {
    return new Checksum() {

      @Override
      public long getValue() {
        return StreamingXXHash32.this.getValue() & 0xFFFFFFFL;
      }

      @Override
      public void reset() {
        StreamingXXHash32.this.reset();
      }

      @Override
      public void update(int b) {
        StreamingXXHash32.this.update(new byte[] {(byte) b}, 0, 1);
      }

      @Override
      public void update(byte[] b, int off, int len) {
        StreamingXXHash32.this.update(b, off, len);
      }

      @Override
      public String toString() {
        return StreamingXXHash32.this.toString();
      }

    };
  }

}
