Token.java

/*
 * Copyright (c) 2013-2017 Cinchapi Inc.
 * 
 * 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.cinchapi.concourse.server.concurrent;

import java.nio.ByteBuffer;

import com.cinchapi.concourse.annotate.PackagePrivate;
import com.cinchapi.concourse.server.io.Byteable;
import com.cinchapi.concourse.server.storage.cache.LazyCache;
import com.cinchapi.concourse.util.ByteBuffers;
import com.cinchapi.concourse.util.TArrays;
import com.google.common.io.BaseEncoding;

/**
 * A {@link Token} wraps multiple other objects.
 * 
 * @author Jeff Nelson
 */
public class Token implements Byteable {

    /**
     * Return the Token encoded in {@code bytes} so long as those bytes adhere
     * to the format specified by the {@link #getBytes()} method. This method
     * assumes that all the bytes in the {@code bytes} belong to the Token. In
     * general, it is necessary to get the appropriate Token slice from the
     * parent ByteBuffer using {@link ByteBuffers#slice(ByteBuffer, int, int)}.
     * 
     * @param bytes
     * @return the Token
     */
    public static Token fromByteBuffer(ByteBuffer bytes) {
        return new Token(bytes);
    }

    /**
     * Return a {@link Token} that wraps the specified {@code objects}.
     * 
     * @param objects
     * @return the Token
     */
    public static Token wrap(Object... objects) {
        Token token = new Token(TArrays.hash(objects));
        token.cardinality = objects.length;
        return token;
    }

    /**
     * Return a {@link Token} that wraps the specified {@code key}. This method
     * takes advantage of caching since the keys are often to be reused
     * frequently.
     * 
     * @param key
     * @return the Token
     */
    public static Token wrap(String key) {
        Token token = cache.get(key);
        if(token == null) {
            token = new Token(TArrays.hash(key));
            token.cardinality = 1;
            cache.put(key, token);
        }
        return token;
    }

    /**
     * The cache of string tokens that represent record keys.
     */
    private static final LazyCache<String, Token> cache = LazyCache
            .withExpectedSize(5000);

    /**
     * The sequence of bytes is a 128-bit (16 byte) hash.
     */
    private final ByteBuffer bytes;

    /**
     * The number of objects that are embedded within the token. This is only
     * used by {@link TokenReadWriteLock} to determine lock granularity.
     */
    @PackagePrivate
    int cardinality = 1;

    /**
     * Construct a new instance.
     * 
     * @param bytes
     */
    protected Token(ByteBuffer bytes) {
        this.bytes = bytes;
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof Token) {
            return getBytes().equals(((Token) obj).getBytes());
        }
        return false;
    }

    @Override
    public ByteBuffer getBytes() {
        return ByteBuffers.asReadOnlyBuffer(bytes);
    }

    @Override
    public int hashCode() {
        return getBytes().hashCode();
    }

    /**
     * "Upgrade" this token by ensuring that the cardinality is greater than 1.
     */
    public void upgrade() {
        this.cardinality += 1;
    }

    @Override
    public int size() {
        return bytes.capacity();
    }

    @Override
    public String toString() {
        return BaseEncoding.base16()
                .encode(ByteBuffers.toByteArray(getBytes())).toLowerCase();
    }

    @Override
    public void copyTo(ByteBuffer buffer) {
        ByteBuffers.copyAndRewindSource(bytes, buffer);
    }

}