/*
 * %CopyrightBegin%
 * 
 * Copyright Ericsson AB 2000-2009. All Rights Reserved.
 * 
 * The contents of this file are subject to the Erlang Public License,
 * Version 1.1, (the "License"); you may not use this file except in
 * compliance with the License. You should have received a copy of the
 * Erlang Public License along with this software. If not, it can be
 * retrieved online at http://www.erlang.org/.
 * 
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
 * the License for the specific language governing rights and limitations
 * under the License.
 * 
 * %CopyrightEnd%
 */
package com.ericsson.otp.erlang;

import java.io.Serializable;

/**
 * Provides a Java representation of Erlang refs. There are two styles of Erlang
 * refs, old style (one id value) and new style (array of id values). This class
 * manages both types.
 */
public class OtpErlangRef extends OtpErlangObject implements Serializable,
	Cloneable {
    // don't change this!
    static final long serialVersionUID = -7022666480768586521L;

    private final String node;
    private final int creation;

    // old style refs have one 18-bit id
    // r6 "new" refs have array of ids, first one is only 18 bits however
    private int ids[] = null;

    /**
     * Create a unique Erlang ref belonging to the local node.
     * 
     * @param self
     *                the local node.
     * 
     * @deprecated use OtpLocalNode:createRef() instead
     */
    @Deprecated
    public OtpErlangRef(final OtpLocalNode self) {
	final OtpErlangRef r = self.createRef();

	ids = r.ids;
	creation = r.creation;
	node = r.node;
    }

    /**
     * Create an Erlang ref from a stream containing a ref encoded in Erlang
     * external format.
     * 
     * @param buf
     *                the stream containing the encoded ref.
     * 
     * @exception OtpErlangDecodeException
     *                    if the buffer does not contain a valid external
     *                    representation of an Erlang ref.
     */
    public OtpErlangRef(final OtpInputStream buf)
	    throws OtpErlangDecodeException {
	final OtpErlangRef r = buf.read_ref();

	node = r.node();
	creation = r.creation();

	ids = r.ids();
    }

    /**
     * Create an old style Erlang ref from its components.
     * 
     * @param node
     *                the nodename.
     * 
     * @param id
     *                an arbitrary number. Only the low order 18 bits will be
     *                used.
     * 
     * @param creation
     *                another arbitrary number. Only the low order 2 bits will
     *                be used.
     */
    public OtpErlangRef(final String node, final int id, final int creation) {
	this.node = node;
	ids = new int[1];
	ids[0] = id & 0x3ffff; // 18 bits
	this.creation = creation & 0x03; // 2 bits
    }

    /**
     * Create a new style Erlang ref from its components.
     * 
     * @param node
     *                the nodename.
     * 
     * @param ids
     *                an array of arbitrary numbers. Only the low order 18 bits
     *                of the first number will be used. If the array contains
     *                only one number, an old style ref will be written instead.
     *                At most three numbers will be read from the array.
     * 
     * @param creation
     *                another arbitrary number. Only the low order 2 bits will
     *                be used.
     */
    public OtpErlangRef(final String node, final int[] ids, final int creation) {
	this.node = node;
	this.creation = creation & 0x03; // 2 bits

	// use at most 82 bits (18 + 32 + 32)
	int len = ids.length;
	this.ids = new int[3];
	this.ids[0] = 0;
	this.ids[1] = 0;
	this.ids[2] = 0;

	if (len > 3) {
	    len = 3;
	}
	System.arraycopy(ids, 0, this.ids, 0, len);
	this.ids[0] &= 0x3ffff; // only 18 significant bits in first number
    }

    /**
     * Get the id number from the ref. Old style refs have only one id number.
     * If this is a new style ref, the first id number is returned.
     * 
     * @return the id number from the ref.
     */
    public int id() {
	return ids[0];
    }

    /**
     * Get the array of id numbers from the ref. If this is an old style ref,
     * the array is of length 1. If this is a new style ref, the array has
     * length 3.
     * 
     * @return the array of id numbers from the ref.
     */
    public int[] ids() {
	return ids;
    }

    /**
     * Determine whether this is a new style ref.
     * 
     * @return true if this ref is a new style ref, false otherwise.
     */
    public boolean isNewRef() {
	return ids.length > 1;
    }

    /**
     * Get the creation number from the ref.
     * 
     * @return the creation number from the ref.
     */
    public int creation() {
	return creation;
    }

    /**
     * Get the node name from the ref.
     * 
     * @return the node name from the ref.
     */
    public String node() {
	return node;
    }

    /**
     * Get the string representation of the ref. Erlang refs are printed as
     * #Ref&lt;node.id&gt;
     * 
     * @return the string representation of the ref.
     */
    @Override
    public String toString() {
	String s = "#Ref<" + node;

	for (int i = 0; i < ids.length; i++) {
	    s += "." + ids[i];
	}

	s += ">";

	return s;
    }

    /**
     * Convert this ref to the equivalent Erlang external representation.
     * 
     * @param buf
     *                an output stream to which the encoded ref should be
     *                written.
     */
    @Override
    public void encode(final OtpOutputStream buf) {
	buf.write_ref(node, ids, creation);
    }

    /**
     * Determine if two refs are equal. Refs are equal if their components are
     * equal. New refs and old refs are considered equal if the node, creation
     * and first id numnber are equal.
     * 
     * @param o
     *                the other ref to compare to.
     * 
     * @return true if the refs are equal, false otherwise.
     */
    @Override
    public boolean equals(final Object o) {
	if (!(o instanceof OtpErlangRef)) {
	    return false;
	}

	final OtpErlangRef ref = (OtpErlangRef) o;

	if (!(node.equals(ref.node()) && creation == ref.creation())) {
	    return false;
	}

	if (isNewRef() && ref.isNewRef()) {
	    return ids[0] == ref.ids[0] && ids[1] == ref.ids[1]
		    && ids[2] == ref.ids[2];
	}
	return ids[0] == ref.ids[0];
    }

    /**
     * Compute the hashCode value for a given ref. This function is compatible
     * with equal.
     *
     * @return the hashCode of the node.
     **/

    @Override
    protected int doHashCode() {
	OtpErlangObject.Hash hash = new OtpErlangObject.Hash(7);
	hash.combine(creation, ids[0]);
	if (isNewRef()) {
	    hash.combine(ids[1], ids[2]);
	}
	return hash.valueOf();
    }
    
    @Override
    public Object clone() {
	final OtpErlangRef newRef = (OtpErlangRef) super.clone();
	newRef.ids = ids.clone();
	return newRef;
    }
}
