package protocolP2P;
import protocolP2P.Payload;
import protocolP2P.RequestResponseCode;
import exception.ProtocolError;
import exception.InternalError;
import exception.SizeError;
import exception.TransmissionError;
import tools.BytesArrayTools;
import java.util.Arrays;
import java.io.UnsupportedEncodingException;

/** Representation of payload for load response.
 * @author	Louis Royer
 * @author	Flavien Haas
 * @author	JS Auge
 * @version	1.0
 */
public class FilePart extends Payload {
	private String filename;
	private long totalSize;
	private long offset;
	private byte[] partialContent;

	/** Constructor (typically used by server) with informations about file part to send as parameters.
	 * @param filename	name of the file to send
	 * @param totalSize	total size of the file to send
	 * @param offset	where in the file begins the part we are sending
	 * @param partialContent	content of the file we send
	 * @throws	InternalError
	 */
	public FilePart(String filename, long totalSize, long offset, byte[] partialContent) throws InternalError {
		super(RequestResponseCode.LOAD_RESPONSE);
		/* asserts to help debugging */
		assert totalSize >= 0 : "totalSize cannot be negative";
		assert partialContent.length != 0 : "partialContent.length cannot be zero"; 
		assert totalSize >= partialContent.length : "totalSize must be greater than partialContent.length";
		assert offset >= 0 : "offset cannot be negative";
		assert filename != null : "filename is required";
		if (totalSize < 0 || partialContent.length == 0 || totalSize < partialContent.length
		    || offset < 0 || filename == null) {
			throw new InternalError();
		}
		this.filename = filename;
		this.totalSize = totalSize;
		this.offset = offset;
		this.partialContent = partialContent;
	}

	/** Constructor (typically used by client) with datagram received as parameter.
	 * @param datagram	the full datagram received
	 * @throws	SizeError
	 * @throws	InternalError
	 * @throws	TransmissionError
	 */
	protected FilePart(byte[] datagram) throws TransmissionError, SizeError, ProtocolError, InternalError {
		super(datagram);
		/* assert to help debugging */
		assert requestResponseCode == RequestResponseCode.LOAD_RESPONSE : "FilePart subclass is incompatible with this datagram, request/response code must be checked before using this constructor";
		/* InternalErrorException */
		if (requestResponseCode != RequestResponseCode.LOAD_RESPONSE) {
			throw new InternalError();
		}
		setOffset(datagram); // this can throw SizeError
		setTotalSize(datagram); // this can throw SizeError
		setFilename(datagram); // this can throw ProtocolError, SizeError
		setPartialContent(datagram); // this can throw SizeError
	}

	/** Returns a byte[] containing datagram with padding.
	 * This datagram is still incomplete and should not be send directly.
	 * ProtocolP2PDatagram will use this method to generate the complete datagram.
	 * @return datagram with padding
	 * @throws	InternalError
	 */
	protected byte[] toDatagram() throws InternalError {
		// compute payload size
		int size = 28 + filename.length() + partialContent.length;
		byte[] datagram = new byte[size]; // java initialize all to zero
		// set request/response code
		datagram[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
		// bits 16-31 are reserved for future use
		setPayloadSize(size - 8, datagram);
		// write offset to datagram (Byte 8)
		BytesArrayTools.write(datagram, 8, offset);
		// write totalSize to datagram (Byte 16)
		BytesArrayTools.write(datagram, 16, totalSize);
		// write filename’s size to datagram
		BytesArrayTools.write(datagram, 24, filename.length());
		// write filename to datagram
		try {
			byte[] bFilename = filename.getBytes("UTF-8");
			int i = filename.length() + 24;
			for (byte b : bFilename) {
				datagram[i] = b;
				i += 1;
			}
			// write partialContent to datagram
			for (byte b: partialContent) {
				datagram[i] = b;
				i += 1;
			}
			return datagram;
		} catch (UnsupportedEncodingException e) {
			throw new InternalError();
		}
	}

	/** Write from bytes 8 to 15 of datagram into offset.
	 * @param datagram	received datagram
	 * @throws	SizeError
	 */
	private void setOffset(byte[] datagram) throws SizeError {
		offset = BytesArrayTools.readLong(datagram, 8);
	}
	/** Write from bytes 16 to 23 of datagram into totalSize.
	 * @param datagram	received datagram
	 * @throws	SizeError
	 */
	private void setTotalSize(byte[] datagram) throws SizeError {
		totalSize = BytesArrayTools.readLong(datagram, 16);
	}

	/** Read filename’s size from bytes 24 to 27 of datagram.
	 * @param datagram	received datagram
	 * @throws	ProtocolError
	 * @throws	SizeError
	 * @return	filename’s size
	 */
	private int getFilenameSize(byte[] datagram) throws SizeError, ProtocolError {
		int size = BytesArrayTools.readInt(datagram, 24); // this can throw SizeError
		// filename size cannot be zero
		if (size == 0) {
			throw new ProtocolError();
		}
		// offset (8B) + totalSize (8B) + filenameSize (4B) = 20B
		if ((20 + size) > getPayloadSize(datagram)) {
			throw new ProtocolError();
		}
		return size;
	}

	/** Write filename from byte 28 to byte (28 + (filenameSize - 1)) of datagram.
	 * @param datagram	received datagram
	 * @throws	ProtocolError
	 * @throws	SizeError
	 * @throws	InternalError
	 */
	private void setFilename(byte[] datagram) throws ProtocolError, SizeError, InternalError {
		int filenameSize = getFilenameSize(datagram); // this can throw ProtocolError or SizeError
		try {
			filename = new String(datagram, 28, filenameSize, "UTF-8");
		} catch (UnsupportedEncodingException e) {
			throw new InternalError();
		}
	}

	/** Write partialContent from byte (28 + filenameSize) to byte (8 + payloadSize) of datagram.
	 * @param datagram	received datagram
	 * @throws	SizeError
	 * @throws	ProtocolError
	 */
	private void setPartialContent(byte[] datagram) throws ProtocolError, SizeError {
		int start = 28 + getFilenameSize(datagram); // this can throw SizeError or ProtocolError
		int end = 8 + getPayloadSize(datagram); // this can throw SizeError
		try {
			partialContent = Arrays.copyOfRange(datagram, start, end);
		} catch (ArrayIndexOutOfBoundsException e) {
			throw new ProtocolError();
		}
	}

	/** partialContent getter.
	 * @return	partialcontent
	 */
	public byte[] getPartialContent() {
		return partialContent;
	}

	/** filename getter.
	 * @return	String
	 */
	public String getFilename() {
		return filename;
	}

	/** offset getter.
	 * @return	offset
	 */
	public long getOffset() {
		return offset;
	}

	/** totalSize getter.
	 * @return	totalSize
	 */
	public long getTotalSize() {
		return totalSize;
	}
}