/*
 * PacketBuilder.java February 2007
 *
 * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>
 *
 * 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.simpleframework.transport;

import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * The <code>PacketBuilder</code> object is used to accumulate octets from
 * provided byte buffers. This will create <code>Packet</code> objects which
 * encapsulate all of the information associated with the byte buffer, and can
 * tell the transport how the buffer should be written. Packets can be either
 * references or copies.
 * 
 * @author Niall Gallagher
 */
class PacketBuilder {

    /**
     * This is packet allocator that is used to create packets.
     */
    private PacketAllocator allocator;

    /**
     * This is the packet within the packet builder being built.
     */
    private Packet packet;

    /**
     * This is the size of the packets that will be created.
     */
    private int size;

    /**
     * Constructor for the <code>PacketBuilder</code> object. This is used to
     * create a builder that can be used to aggregate multiple byte buffers in
     * to a single packet object. This will limit the number of packets that can
     * be created by this builder.
     */
    public PacketBuilder() {
        this(3);
    }

    /**
     * Constructor for the <code>PacketBuilder</code> object. This is used to
     * create a builder that can be used to aggregate multiple byte buffers in
     * to a single packet object. This will limit the number of packets that can
     * be created by this builder.
     * 
     * @param queue
     *            this is a limit to the number of packets built
     */
    public PacketBuilder(int queue) {
        this(queue, 4096);
    }

    /**
     * Constructor for the <code>PacketBuilder</code> object. This is used to
     * create a builder that can be used to aggregate multiple byte buffers in
     * to a single packet object. This will limit the number of packets that can
     * be created by this builder.
     * 
     * @param queue
     *            this is a limit to the number of packets built
     * @param size
     *            this is the size of the packets to be built
     */
    public PacketBuilder(int queue, int size) {
        this.allocator = new PacketAllocator(queue, size);
        this.size = size;
    }

    /**
     * This is used to acquire the current packet that has been built within the
     * builder. When the packet is returned from this method another packet is
     * allocated for the next build.
     * 
     * @return this returns the current packet within the builder
     */
    public Packet build() throws IOException {
        Packet local = null;

        if (this.packet != null) {
            int length = this.packet.length();

            if (length <= 0) {
                this.packet.close();
            } else {
                local = this.packet;
            }
            this.packet = null;
        }
        return local;
    }

    /**
     * This is used to build the a <code>Packet</code> within the builder using
     * the provided buffer. The returned packet will contain the accumulated
     * bytes from calls to the build method. If the previous packets are not
     * closed this method will block until such time as the packet is closed.
     * 
     * @param buffer
     *            this is the buffer to be added to the packet
     * 
     * @return this returns the packet containing the bytes
     */
    public Packet build(ByteBuffer buffer) throws IOException {
        int ready = buffer.remaining();

        if (this.packet != null) return this.build(buffer, this.packet);
        if (ready > this.size) return this.allocator.allocate(buffer);
        if (ready > 0) {
            if (this.packet == null) {
                this.packet = this.allocator.allocate();
            }
            return this.build(buffer, this.packet);
        }
        return null;
    }

    /**
     * This is used to build the a <code>Packet</code> within the builder using
     * the provided buffer. The returned packet will contain the accumulated
     * bytes from calls to the build method. If the previous packets are not
     * closed this method will block until such time as the packet is closed.
     * 
     * @param buffer
     *            this is the buffer to be added to the packet
     * @param packet
     *            this is the packet to add the buffer to
     * 
     * @return this returns the packet containing the bytes
     */
    private Packet build(ByteBuffer buffer, Packet packet) throws IOException {
        int ready = buffer.remaining();
        int length = packet.length();
        int space = packet.space();

        if (ready <= space) {
            packet.append(buffer);
        } else {
            int capacity = buffer.capacity();

            if (length == 0) return this.allocator.allocate(buffer);
            if (space < capacity) {
                if (space > 0) {
                    packet.append(buffer);
                }
                return this.build();
            }
            return this.allocator.allocate(buffer);
        }
        if (space == ready) return this.build();
        return null;
    }
}