// SelectTCPServer.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <winsock2.h>
#include <stdio.h>
#include <conio.h>

#pragma comment (lib,"ws2_32.lib")

#define SERVER_ADDR "127.0.0.1"
#define PORT 5500
#define BUFF_SIZE 2048

void processData(char *, char *);
int Receive(SOCKET, char *, int, int);
int Send(SOCKET, char *, int, int);

int _tmain(int argc, _TCHAR* argv[])
{
	//Step 1: Initiate WinSock
	WSADATA wsaData;
	WORD wVersion = MAKEWORD(2, 2);
	if (WSAStartup(wVersion, &wsaData))
		printf("Version is not supported\n");

	//Step 2: Construct socket	
	SOCKET listenSock;
	listenSock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

	//Step 3: Bind address to socket
	sockaddr_in serverAddr;
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_port = htons(PORT);
	serverAddr.sin_addr.s_addr = inet_addr(SERVER_ADDR);

	if (bind(listenSock, (sockaddr *)&serverAddr, sizeof(serverAddr)))
	{
		printf("Error! Cannot bind this address.");
		_getch();
		return 0;
	}

	//Step 4: Listen request from client
	if (listen(listenSock, 10)) {
		printf("Error! Cannot listen.");
		_getch();
		return 0;
	}

	printf("Server started!\n");


	SOCKET client[FD_SETSIZE], connSock;
	fd_set readfds, initfds; //use initfds to initiate readfds at the begining of every loop step
	sockaddr_in clientAddr;
	int ret, nEvents, clientAddrLen;
	char rcvBuff[BUFF_SIZE], sendBuff[BUFF_SIZE];

	for (int i = 0; i < FD_SETSIZE; i++)
		client[i] = 0;	// 0 indicates available entry

	FD_ZERO(&initfds);
	FD_SET(listenSock, &initfds);

	//Step 5: Communicate with clients
	while (1) {
		readfds = initfds;		/* structure assignment */
		nEvents = select(0, &readfds, 0, 0, 0);
		if (nEvents < 0) {
			printf("\nError! Cannot poll sockets: %d", WSAGetLastError());
			break;
		}

		//new client connection
		if (FD_ISSET(listenSock, &readfds)) {
			clientAddrLen = sizeof(clientAddr);
			if ((connSock = accept(listenSock, (sockaddr *)&clientAddr, &clientAddrLen)) < 0) {
				printf("\nError! Cannot accept new connection: %d", WSAGetLastError());
				break;
			}
			else {
				printf("You got a connection from %s\n", inet_ntoa(clientAddr.sin_addr)); /* prints client's IP */

				int i;
				for (i = 0; i < FD_SETSIZE; i++)
					if (client[i] == 0) {
						client[i] = connSock;
						FD_SET(client[i], &initfds);						
						break;
					}

				if (i == FD_SETSIZE) {
					printf("\nToo many clients.");
					closesocket(connSock);
				}

				if (--nEvents == 0)
					continue; //no more event
			}
		}

		//receive data from clients
		for (int i = 0; i < FD_SETSIZE; i++) {
			if (client[i] == 0)
				continue;
			
			if (FD_ISSET(client[i], &readfds)) {
				ret = Receive(client[i], rcvBuff, BUFF_SIZE, 0);
				if (ret <= 0) {
					FD_CLR(client[i], &initfds);
					closesocket(client[i]);
					client[i] = 0;
				}
				else if (ret > 0) {
					processData(rcvBuff, sendBuff);
					Send(client[i], sendBuff, ret, 0);
				}
			}

			if (--nEvents <= 0)
				continue; //no more event
		}

	}

	closesocket(listenSock);
	WSACleanup();
	return 0;
}

/* The processData function copies the input string to output
* @param in Pointer to input string
* @param out Pointer to output string
* @return No return value
*/
void processData(char *in, char *out) {
	memcpy(out, in, BUFF_SIZE);
}

/* The recv() wrapper function */
int Receive(SOCKET s, char *buff, int size, int flags) {
	int n;

	n = recv(s, buff, size, flags);
	if (n == SOCKET_ERROR)
		printf("Error: %", WSAGetLastError());

	return n;
}

/* The send() wrapper function*/
int Send(SOCKET s, char *buff, int size, int flags) {
	int n;

	n = send(s, buff, size, flags);
	if (n == SOCKET_ERROR)
		printf("Error: %", WSAGetLastError());

	return n;
}