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Contains common utility code, reusable outside Hudson.
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/**
 * The MIT License
 *
 * Copyright (c) 2010-2011 Sonatype, Inc. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package org.hudsonci.utils.id;

import com.thoughtworks.xstream.annotations.XStreamAlias;
import com.thoughtworks.xstream.annotations.XStreamAsAttribute;

import java.util.Collection;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Provides a general identifier for objects.
 *
 * String representation should follow the default behavior of {@link Object#toString}.
 * {@link #hashCode}/{@link #equals} behavior differs to make the OID unique based on
 * {@link #type} and {@link #hash}.  When constructing from an object the hash is always
 * the {@link System#identityHashCode}.
 *
 * @author Jason Dillon
 * @since 2.1.0
 */
@XStreamAlias("oid")
public class OID
    implements ID
{
    public static final OID NULL = new OID();

    @XStreamAsAttribute
    private final String type;

    @XStreamAsAttribute
    private final int hash;

    private OID(final String type, final int hash) {
        this.type = checkNotNull(type);
        this.hash = hash;
    }

    private OID() {
        type = null;
        hash = System.identityHashCode(this);
    }

    public String getType() {
        return type;
    }

    public int getHash() {
        return hash;
    }

    @Override
    public boolean equals(final Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof OID)) {
            return false;
        }

        OID that = (OID) obj;

        if (hash != that.hash) {
            return false;
        }
        if (type != null ? !type.equals(that.type) : that.type != null) {
            return false;
        }

        return true;
    }

    @Override
    public int hashCode() {
        int result = type != null ? type.hashCode() : 0;
        result = 31 * result + hash;
        return result;
    }

    @Override
    public String toString() {
        if (this == NULL) {
            return null;
        }
        return String.format("%s@%x", type, hash);
    }

    public static OID get(final Object obj) {
        if (obj == null) {
            return NULL;
        }
        return new OID(obj.getClass().getName(), System.identityHashCode(obj));
    }

    /**
     * @see #get
     */
    public static OID oid(final Object obj) {
        return get(obj);
    }

    public static OID parse(final String spec) {
        assert spec != null;
        String[] items = spec.split("@");
        if (items.length != 2) {
            throw new IllegalArgumentException();
        }
        return new OID(items[0], Integer.parseInt(items[1], 16));
    }

    public static String render(final Object obj) {
        assert obj != null;
        return get(obj).toString();
    }

    public static  T find(final Collection items, final String id) {
        assert items != null;
        assert id != null;

        for (T item : items) {
            if (OID.render(item).equals(id)) {
                return item;
            }
        }

        return null;
    }

    public static  T find(final Collection items, final OID id) {
        assert id != null;
        return find(items, id.toString());
    }
}