package envoy.util;

import java.io.*;

/**
 * Defines utility methods related to serialization.
 *
 * @author Kai S. K. Engelbart
 * @since Envoy Common v0.2-alpha
 */
public final class SerializationUtils {

	private SerializationUtils() {}

	/**
	 * Converts an integer into a byte array.
	 *
	 * @param n the integer to convert
	 * @return a byte array of length 4
	 * @since Envoy Common v0.2-alpha
	 */
	public static byte[] intToBytes(int n) {
		return new byte[] { (byte) (n >>> 24), (byte) (n >>> 16), (byte) (n >>> 8), (byte) n };
	}

	/**
	 * Converts four bytes in byte array to an integer
	 *
	 * @param bytes  the bytes to convert from
	 * @param offset the offset at which four bytes are read
	 * @return the converted integer
	 * @since Envoy Common v0.2-alpha
	 */
	public static int bytesToInt(byte[] bytes, int offset) {
		return (bytes[offset] & 0xFF) << 24 | (bytes[offset + 1] & 0xFF) << 16
			| (bytes[offset + 2] & 0xFF) << 8
			| (bytes[offset + 3] & 0xFF) << 0;
	}

	/**
	 * Deserializes an arbitrary {@link Serializable} object from a file.
	 *
	 * @param <T>             the type of the serialized object
	 * @param file            the file to deserialize from
	 * @param serializedClass the class of the object to deserialize
	 * @return the deserialized object
	 * @throws IOException            if something failed while deserializing the object
	 * @throws ClassNotFoundException if the deserialized object can not be linked to a class
	 * @since Envoy Common v0.2-alpha
	 */
	public static <T extends Serializable> T read(File file, Class<T> serializedClass)
		throws IOException, ClassNotFoundException {
		if (file == null)
			throw new NullPointerException("File is null");
		return read(new FileInputStream(file), serializedClass);
	}

	/**
	 * Deserializes an arbitrary {@link Serializable} object from a byte array.
	 *
	 * @param <T>             the type of the serialized object
	 * @param bytes           the array in which the serialized object is stored
	 * @param serializedClass the class of the serialized object
	 * @return the deserialized object
	 * @throws IOException            if something failed while deserializing the object
	 * @throws ClassNotFoundException if the deserialized object can not be linked to a class
	 * @since Envoy Common v0.2-alpha
	 */
	public static <T extends Serializable> T read(byte[] bytes, Class<T> serializedClass)
		throws IOException, ClassNotFoundException {
		return read(new ByteArrayInputStream(bytes), serializedClass);
	}

	/**
	 * Deserializes an arbitrary {@link Serializable} object from a stream.
	 *
	 * @param <T>             the type of the serialized object
	 * @param in              the {@link InputStream} of a serialized Object
	 * @param serializedClass the object type to convert the deserialized object into
	 * @return the deserialized object
	 * @throws IOException            if something failed while deserializing the object
	 * @throws ClassNotFoundException if the deserialized object can not be linked to a class
	 * @since Envoy Common v0.2-alpha
	 */
	public static <T extends Serializable> T read(InputStream in, Class<T> serializedClass)
		throws IOException, ClassNotFoundException {
		try (ObjectInputStream oin = new ObjectInputStream(in)) {
			return serializedClass.cast(oin.readObject());
		}
	}

	/**
	 * Serializes arbitrary objects to a file.
	 *
	 * @param file the file to serialize to
	 * @param objs the objects to serialize
	 * @throws IOException if an error occurred during serialization
	 * @since Envoy Common v0.2-alpha
	 */
	public static void write(File file, Object... objs) throws IOException {
		if (file == null)
			throw new NullPointerException("File is null");
		if (objs == null)
			throw new NullPointerException("Null array passed to serialize");
		if (!file.exists()) {
			file.getParentFile().mkdirs();
			file.createNewFile();
		}
		try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file))) {
			for (var obj : objs)
				out.writeObject(obj);
		}
	}

	/**
	 * Serializes an arbitrary object to a byte array.
	 *
	 * @param obj the object to serialize
	 * @return a byte array containing the serialized object
	 * @throws IOException if the serialization failed
	 * @since Envoy Common v0.2-alpha
	 */
	public static byte[] writeToByteArray(Object obj) throws IOException {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		try (ObjectOutputStream oout = new ObjectOutputStream(baos)) {
			oout.writeObject(obj);
		}
		return baos.toByteArray();
	}

	/**
	 * Serializes an object and writes it into an output stream preceded by 4 bytes containing the
	 * number of serialized bytes.
	 *
	 * @param obj the object to serialize
	 * @param out the output stream to serialize to
	 * @throws IOException if an error occurred during serialization
	 * @since Envoy Common v0.2-alpha
	 */
	public static void writeBytesWithLength(Object obj, OutputStream out) throws IOException {
		// Serialize object to byte array
		byte[] objBytes = writeToByteArray(obj);

		// Get length of byte array in bytes
		byte[] objLen = intToBytes(objBytes.length);

		// Write length and byte array
		out.write(objLen);
		out.write(objBytes);
	}
}