/**
 *
 * Copyright 2003-2007 Jive Software.
 *
 * 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 org.jivesoftware.smack.packet;

import org.jivesoftware.smack.util.PacketUtil;
import org.jivesoftware.smack.util.StringUtils;
import org.jivesoftware.smack.util.XmlStringBuilder;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Locale;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Base class for XMPP packets. Every packet has a unique ID (which is automatically
 * generated, but can be overridden). Optionally, the "to" and "from" fields can be set.
 *
 * @author Matt Tucker
 */
public abstract class Packet extends TopLevelStreamElement {

    public static final String TEXT = "text";
    public static final String ITEM = "item";

    protected static final String DEFAULT_LANGUAGE =
            java.util.Locale.getDefault().getLanguage().toLowerCase(Locale.US);

    /**
     * A prefix helps to make sure that ID's are unique across multiple instances.
     */
    private static String prefix = StringUtils.randomString(5) + "-";

    /**
     * Keeps track of the current increment, which is appended to the prefix to
     * forum a unique ID.
     */
    private static AtomicLong id = new AtomicLong();

    private String packetID = null;
    private String to = null;
    private String from = null;
    private final List<PacketExtension> packetExtensions
            = new CopyOnWriteArrayList<PacketExtension>();

    private XMPPError error = null;

    /**
     * Optional value of the 'xml:lang' attribute of the outermost element of
     * the stanza.
     * <p>
     * Such an attribute is defined for all stanza types. For IQ, see for
     * example XEP-50 3.7:
     * "The requester SHOULD provide its locale information using the "xml:lang
     * " attribute on either the <iq/> (RECOMMENDED) or <command/> element."
     * </p>
     */
    protected String language;

    public Packet() {
        this(prefix + Long.toString(id.incrementAndGet()));
    }

    public Packet(String packetID) {
        setPacketID(packetID);
    }

    public Packet(Packet p) {
        packetID = p.getPacketID();
        to = p.getTo();
        from = p.getFrom();
        error = p.error;

        // Copy extensions
        for (PacketExtension pe : p.getExtensions()) {
            addExtension(pe);
        }
    }

    /**
     * Returns the unique ID of the packet. The returned value could be <tt>null</tt> when
     * ID_NOT_AVAILABLE was set as the packet's id.
     *
     * @return the packet's unique ID or <tt>null</tt> if the packet's id is not available.
     */
    public String getPacketID() {
        return packetID;
    }

    /**
     * Sets the unique ID of the packet. To indicate that a packet has no id
     * pass the constant ID_NOT_AVAILABLE as the packet's id value.
     *
     * @param packetID the unique ID for the packet.
     */
    public void setPacketID(String packetID) {
        this.packetID = packetID;
    }

    /**
     * Returns who the packet is being sent "to", or <tt>null</tt> if
     * the value is not set. The XMPP protocol often makes the "to"
     * attribute optional, so it does not always need to be set.<p>
     *
     * @return who the packet is being sent to, or <tt>null</tt> if the
     *      value has not been set.
     */
    public String getTo() {
        return to;
    }

    /**
     * Sets who the packet is being sent "to". The XMPP protocol often makes
     * the "to" attribute optional, so it does not always need to be set.
     *
     * @param to who the packet is being sent to.
     */
    public void setTo(String to) {
        this.to = to;
    }

    /**
     * Returns who the packet is being sent "from" or <tt>null</tt> if
     * the value is not set. The XMPP protocol often makes the "from"
     * attribute optional, so it does not always need to be set.<p>
     *
     * @return who the packet is being sent from, or <tt>null</tt> if the
     *      value has not been set.
     */
    public String getFrom() {
        return from;
    }

    /**
     * Sets who the packet is being sent "from". The XMPP protocol often
     * makes the "from" attribute optional, so it does not always need to
     * be set.
     *
     * @param from who the packet is being sent to.
     */
    public void setFrom(String from) {
        this.from = from;
    }

    /**
     * Returns the error associated with this packet, or <tt>null</tt> if there are
     * no errors.
     *
     * @return the error sub-packet or <tt>null</tt> if there isn't an error.
     */
    public XMPPError getError() {
        return error;
    }

    /**
     * Sets the error for this packet.
     *
     * @param error the error to associate with this packet.
     */
    public void setError(XMPPError error) {
        this.error = error;
    }

    /**
     * Returns the xml:lang of this Stanza, or null if one has not been set.
     *
     * @return the xml:lang of this Stanza, or null.
     */
    public String getLanguage() {
        return language;
    }

    /**
     * Sets the xml:lang of this Stanza.
     *
     * @param language the xml:lang of this Stanza.
     */
    public void setLanguage(String language) {
        this.language = language;
    }

    /**
     * Returns an unmodifiable collection of the packet extensions attached to the packet.
     *
     * @return the packet extensions.
     */
    public synchronized Collection<PacketExtension> getExtensions() {
        if (packetExtensions == null) {
            return Collections.emptyList();
        }
        return Collections.unmodifiableList(new ArrayList<PacketExtension>(packetExtensions));
    }

    /**
     * Returns the first extension of this packet that has the given namespace.
     *
     * @param namespace the namespace of the extension that is desired.
     * @return the packet extension with the given namespace.
     */
    public PacketExtension getExtension(String namespace) {
        return getExtension(null, namespace);
    }

    /**
     * Returns the first packet extension that matches the specified element name and
     * namespace, or <tt>null</tt> if it doesn't exist. If the provided elementName is null,
     * only the namespace is matched. Packet extensions are
     * are arbitrary XML sub-documents in standard XMPP packets. By default, a 
     * DefaultPacketExtension instance will be returned for each extension. However, 
     * PacketExtensionProvider instances can be registered with the 
     * {@link org.jivesoftware.smack.provider.ProviderManager ProviderManager}
     * class to handle custom parsing. In that case, the type of the Object
     * will be determined by the provider.
     *
     * @param elementName the XML element name of the packet extension. (May be null)
     * @param namespace the XML element namespace of the packet extension.
     * @return the extension, or <tt>null</tt> if it doesn't exist.
     */
    public <PE extends PacketExtension> PE getExtension(String elementName, String namespace) {
        if (namespace == null) {
            return null;
        }
        return PacketUtil.packetExtensionfromCollection(packetExtensions, elementName, namespace);
    }

    /**
     * Adds a packet extension to the packet. Does nothing if extension is null.
     *
     * @param extension a packet extension.
     */
    public void addExtension(PacketExtension extension) {
        if (extension == null) return;
        packetExtensions.add(extension);
    }

    /**
     * Adds a collection of packet extensions to the packet. Does nothing if extensions is null.
     * 
     * @param extensions a collection of packet extensions
     */
    public void addExtensions(Collection<PacketExtension> extensions) {
        if (extensions == null) return;
        packetExtensions.addAll(extensions);
    }

    /**
     * Removes a packet extension from the packet.
     *
     * @param extension the packet extension to remove.
     */
    public void removeExtension(PacketExtension extension)  {
        packetExtensions.remove(extension);
    }

    /**
     * Returns the extension sub-packets (including properties data) as an XML
     * String, or the Empty String if there are no packet extensions.
     *
     * @return the extension sub-packets as XML or the Empty String if there
     * are no packet extensions.
     */
    protected synchronized CharSequence getExtensionsXML() {
        XmlStringBuilder xml = new XmlStringBuilder();
        // Add in all standard extension sub-packets.
        for (PacketExtension extension : getExtensions()) {
            xml.append(extension.toXML());
        }
        return xml;
    }

    /**
     * Returns the default language used for all messages containing localized content.
     * 
     * @return the default language
     */
    public static String getDefaultLanguage() {
        return DEFAULT_LANGUAGE;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Packet packet = (Packet) o;

        if (error != null ? !error.equals(packet.error) : packet.error != null) { return false; }
        if (from != null ? !from.equals(packet.from) : packet.from != null) { return false; }
        if (!packetExtensions.equals(packet.packetExtensions)) { return false; }
        if (packetID != null ? !packetID.equals(packet.packetID) : packet.packetID != null) {
            return false;
        }
        if (to != null ? !to.equals(packet.to) : packet.to != null)  { return false; }
        return true;
    }

    @Override
    public int hashCode() {
        int result = 1;
        result = 31 * result + (packetID != null ? packetID.hashCode() : 0);
        result = 31 * result + (to != null ? to.hashCode() : 0);
        result = 31 * result + (from != null ? from.hashCode() : 0);
        result = 31 * result + packetExtensions.hashCode();
        result = 31 * result + (error != null ? error.hashCode() : 0);
        return result;
    }

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

    /**
     * Add to, from, id and 'xml:lang' attributes
     *
     * @param xml
     */
    protected void addCommonAttributes(XmlStringBuilder xml) {
        xml.optAttribute("id", getPacketID());
        xml.optAttribute("to", getTo());
        xml.optAttribute("from", getFrom());
        xml.xmllangAttribute(getLanguage());
    }
}