//This is the server program.
import java.io;
import java.net;

public class Server {
	//We specify the port 5001, which is what we will listen to for incoming connections
	Integer OUR_PORT = 5001;

	public static void main(String[] args) throws IOException {
		Integer NUM_POSSIBLE_CONNECTIONS = 1;
		ServerSocket ourServerSocket;
		
		try {
			//Create the server socket
			ourServerSocket = new ServerSocket(OUR_PORT, NUM_POSSIBLE_CONNECTIONS);
		} catch(IOException e) {
			System.out.println("Client::main::creating_the_socket:: " + e);
			System.exit(1);
		}
		try {
			//Block on accepting connections. Once it has received a connection it will return a socket for us to use.
			Socket incomingConnectionSocket = ourServerSocket.accept();

			//If we get here we are no longer blocking, so we accepted a new connection
			System.out.println("We received a connection!");

			//We have yet to block again, so we can handle this connection however we would like to.
			//For now, let's send a message and then wait for the response.
			DataInputStream inputStream = new DataInputStream(incomingConnectionSocket.getInputStream());
			DataOutputStream outputStream = new DataOutputStream(incomingConnectionSocket.getOutputStream());

			//Let's send a message to our new friend
			byte[] msgToClient = String("What class is this video for?").getBytes();
			Integer msgToClientLength = msgToClient.length;

			//Our self-inflicted protocol says we send the length first
			outputStream.writeInt(msgToClientLength);
			//Then we can send the message
			outputStream.write(msgToClient, 0, msgToClientLength);

			//Now we wait for their response.
			Integer msgLength = 0;
			//Try to read an integer from our input stream. This will block if there is nothing.
			msgLength = inputStream.readInt();

			//If we got here that means there was an integer to 
			// read and we have the length of the rest of the next message.
			System.out.println("Received a message length of: " + msgLength);

			//Try to read the incoming message.
			byte[] incomingMessage = new byte[msgLength];
			incomingInputStream.readFully(incomingMessage, 0, msgLength);

			//You could have used .read(byte[] incomingMessage), however this will read 
			// *potentially* incomingMessage.length bytes, maybe less.
			//Whereas .readFully(...) will read exactly msgLength number of bytes. 

			System.out.println("Received Message: " + incomingMessage);

			//Close streams and then sockets
			inputStream.close();
			outputStream.close();
			incomingConnectionSocket.close();
			ourServerSocket.close();

		} catch (IOException e) {
            System.out.println("Server::main::accepting_connections:: " + e);
            System.exit(1);
        }

	}
}