package rtp;

import org.dreier.bitarray.BitArrayField;

/**
 * RTP packet header.
 * @author Frederic Dreier
 *
 */
public class RtpHeaderBA {
	
	@BitArrayField(offset = 0, length = 2)
	public int version;

	@BitArrayField(offset = 2, length = 1)
	public boolean padding;

	@BitArrayField(offset = 3, length = 1)
	public boolean extension;

	@BitArrayField(offset = 4, length = 4)
	public int ccCsrc;
	
	@BitArrayField(offset = 8, length = 1)
	public boolean marker;

	@BitArrayField(offset = 9, length = 7)
	public int payloadType;

	@BitArrayField(offset = 16, length = 16)
	public int sequenceNbr;

	@BitArrayField(offset = 32, length = 32)
	public long timestamp;

	@BitArrayField(offset = 64, length = 32)
	public long ssrc;

	@BitArrayField(offset = 96, length = 32)
	public long csrc;

}

		byte[] data = ...;

		// prepare empty structure
		RtpHeaderBA header = new RtpHeaderBA();

		// extract it
		BitExtractor b = new BitExtractor();
		b.parse(data, header);
		
		// plenty of place for other code here !! 
		...

/* 
 * (C) Copyright 2007-2008, by Frederic Dreier
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU General Public License 
 * along with this library; if not, write to the Free Software Foundation, 
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 */
package org.dreier.bitarray;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)

/**
 * Annotation used by BitExtractor.
 * @author dreier Frederic Dreier
 */
public @interface BitArrayField {
	int offset();

	int length();

	boolean unsigned() default true;
}

/* 
 * (C) Copyright 2007-2008, by Frederic Dreier
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU General Public License 
 * along with this library; if not, write to the Free Software Foundation, 
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 */
package org.dreier.bitarray;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * Quick and Dirty implementation of a Bit Extractor.
 *  
 * @author Frederic Dreier
 */
public class BitExtractor {
	private static final int[] MASK_A = { 0xFF, 0x7F, 0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01 };

	private static final int[] MASK_P = { 0xFF, 0xFE, 0xFC, 0xF8, 0xF0, 0xE0, 0xC0, 0x80, 0x00 };

	private HashMap mapping = new HashMap();

	public MetaData register(Class clazz) {
		synchronized (mapping) {
			MetaData md = mapping.get(clazz);
			if (md == null) {
				// retieve annotations for this class
				md = new MetaData();
				for (Field fld : clazz.getDeclaredFields()) {
					int cnt = 0;
					for (Annotation ant : fld.getAnnotations()) {
						if (ant instanceof BitArrayField) {
							// check consistency.
							if (cnt > 0) {
								throw new RuntimeException("Field[" + fld.getName() + "] of class [" + clazz
										+ "] should only have one annotation of type 'BitArrayField'.");
							}
							cnt++;
							// update metadata
							BitArrayField bfAnt = (BitArrayField) ant;
							MetaField mf = new MetaField(bfAnt.offset(), bfAnt.length(), bfAnt.unsigned(), fld
									.getType(), fld);
							md.add(mf);
						}
					}
				}
				// cache meta data
				mapping.put(clazz, md);
			}
			return md;
		}
	}

	/**
	 * Parse data hand update header.
	 * 
	 * @param data
	 * @param struct
	 */
	public void parse(byte[] data, Object struct) {
		// get MetaData
		MetaData md = register(struct.getClass());
		for (MetaField f : md.fields) {
			if (f.type.equals(int.class) || f.type.equals(long.class)) {
				// integer field...

				int bByte = f.offset / 8;
				int bMask = MASK_A[f.offset % 8];
				int end = f.offset + f.length;
				int pads = 8 - (f.offset + f.length) % 8;
				int eByte = end / 8;
				// first byte
				long acc = data[bByte] & bMask;
				if (bByte == eByte) {
					acc = acc >> pads;
				} else {
					// loop bytes
					for (int ptr = bByte + 1; ptr < eByte; ptr++) {
						acc = (acc << 8) | (data[ptr] & 0xFF);
					}
					// last byte (could be smaller than 8 bits)
					acc = (data[eByte] & MASK_P[pads] | (acc << 8)) >> pads;
				}
				// set value in struct
				try {
					if (f.type.equals(int.class)) {
						// int
						f.classField.setInt(struct, (int) acc);
					} else {
						// long
						f.classField.setLong(struct, acc);
					}
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				}
			} else if (f.type.equals(boolean.class)) {
				// boolean
				if (f.length != 1) {
					throw new RuntimeException("field [" + f.classField.getName()
							+ "] is a boolean and should have a length of '1'.");
				}
				int bIdx = f.offset / 8;
				int b = f.offset - bIdx * 8;
				int mask = 1 << (7 - b);
				int acc = data[bIdx] & mask;
				// set value in struct
				try {
					f.classField.setBoolean(struct, acc != 0);
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				}
			} else if (f.type.equals(String.class)) {
				// String (only on plain byte)
				if (f.length % 8 != 0) {
					throw new RuntimeException("field [" + f.classField.getName()
							+ "] is a String and should have a length of 'n*8'.");
				}
				if (f.offset % 8 != 0) {
					throw new RuntimeException("field [" + f.classField.getName()
							+ "] is a String and should have an offset of 'n*8'.");
				}
				int charCnt = f.length / 8;
				int bByte = f.offset / 8;
				String result = new String(data, bByte, charCnt);
				// set value in struct
				try {
					f.classField.set(struct, result);
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				}
			} else {
				throw new RuntimeException("Unsupported class [" + f.type + "]");
			}
		}
	}

	// ================================================================
	// Inner classes
	// ================================================================
	/**
	 * A class meta data.
	 * 
	 * @author Frederic Dreier
	 */
	public class MetaData {
		private ArrayList fields = new ArrayList();

		/**
		 * Add a field. Covenient method
		 * 
		 * @param field
		 */
		public void add(MetaField field) {
			fields.add(field);
		}

		/**
		 * Get fields.
		 * 
		 * @return
		 */
		public List getFields() {
			return fields;
		}
	}

	/**
	 * Bit array field.
	 * 
	 * @author dreier
	 */
	public class MetaField {
		private int offset;

		private int length;

		private Field classField;

		private boolean unsigned;

		private Class type;

		public MetaField(int offset, int length, boolean unsigned, Class type, Field classField) {
			this.offset = offset;
			this.length = length;
			this.unsigned = unsigned;
			this.type = type;
			this.classField = classField;

		}

		public int getLength() {
			return length;
		}

		public int getOffset() {
			return offset;
		}

		public Class getType() {
			return type;
		}

		public boolean isUnsigned() {
			return unsigned;
		}

	}

	
}