#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <vector>
#include <algorithm>
#include <iostream>

using namespace std;

void sig_chld(int signo)
{
	pid_t pid;
	int stat;
	while ((pid = waitpid(-1, &stat, WNOHANG)) > 0) 
		printf("child %d terminated.\n", pid);
	return ;
}

int main(int argc, char * argv[])
{
	int sockfd, rec_sock;
	socklen_t len;
	vector<int> sock_vector;
	// vector<int>::iterator itr;
	struct sockaddr_in addr, recaddr;
	struct sigaction abc;
	char buf[100];
	fd_set allset, rset;
	int maxfd;

	abc.sa_handler = sig_chld;
	sigemptyset(&abc.sa_mask);
	abc.sa_flags = 0;

	sigaction(SIGCHLD, &abc, NULL);

	if (argc < 2) {
		printf("Usage: a.out port.\n");
		exit(0);
	}

	if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
		perror(": Can't get socket");
		exit(1);
	}

	addr.sin_addr.s_addr = INADDR_ANY;
	addr.sin_family = AF_INET;
	addr.sin_port = htons((short)atoi(argv[1]));

	if (bind(sockfd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror(": bind");
		exit(1);
	}


	len = sizeof(addr);
	if (getsockname(sockfd, (struct sockaddr *)&addr, &len) < 0) {
		perror(": can't get name");
		_exit(1);
	}

	printf("ip = %s, port = %d\n", inet_ntoa(addr.sin_addr), htons(addr.sin_port));

	if (listen(sockfd, 5) < 0) {
		perror(": bind");
		exit(1);
	}


	FD_ZERO(&allset);
	FD_SET(sockfd, &allset);
	maxfd = sockfd;

	sock_vector.clear();

	while (1) {
		rset = allset;
		select(maxfd+1, &rset, NULL, NULL, NULL);
		if (FD_ISSET(sockfd, &rset)) {
			/* somebody tries to connect */
			if ((rec_sock = accept(sockfd, (struct sockaddr *)(&recaddr), &len)) < 0) {
				if (errno == EINTR)
					continue;
				else {
					perror(":accept error");
					exit(1);
				}
			}

			/*
			if (rec_sock < 0) {
				perror(": accept");
				exit(1);
			}
			*/

			/* print the remote socket information */

			printf("remote machine = %s, port = %d.\n",
					inet_ntoa(recaddr.sin_addr), ntohs(recaddr.sin_port)); 

			sock_vector.push_back(rec_sock);
			FD_SET(rec_sock, &allset);
			if (rec_sock > maxfd) maxfd = rec_sock;
		}

		// vector<int>::iterator itr = sock_vector.begin();
		auto itr = sock_vector.begin(); 
		while (itr != sock_vector.end()) {
			int num, fd;
			fd = *itr;
			if (FD_ISSET(fd, &rset)) {
				num = read(fd, buf, 100);
				if (num == 0) {
					/* client exits */
					close(fd);
					FD_CLR(fd, &allset);
					itr = sock_vector.erase(itr);
					continue;
				} else {
					write(fd, buf, num);
				}
			}
			++itr;
		}

		maxfd = sockfd;
		if (!sock_vector.empty()) {
			maxfd = max(maxfd, *max_element(sock_vector.begin(),
						sock_vector.end()));
		}
	}
}