#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>	/* For atoi() */
#include <ctype.h>	/* For toupper() */
#include <unistd.h>	/* For read() */

/* Same function as we've seen earlier */
int open_listen(int port)
{
    int fd;
    struct sockaddr_in serverAddr;
    int optVal;

    fd = socket(AF_INET, SOCK_STREAM, 0);
    if(fd < 0) {
        perror("Error creating socket");
        exit(1);
    }

    optVal = 1;
    if(setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &optVal, sizeof(int)) < 0) {
	perror("Error setting socket option");
	exit(1);
    }
    
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(port);
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);

    if(bind(fd, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr_in)) < 0){
	perror("Error binding socket to port");
	exit(1);
    }
    if(listen(fd, SOMAXCONN) < 0) {
	perror("Error listening");
	exit(1);
    }

    return fd;
}

/* Same function as we've seen earlier */
char* capitalise(char* buffer, int len)
{
    int i;

    for(i=0; i<len; i++) {
	buffer[i] = (char)toupper((int)buffer[i]);
    }
    return buffer;
}
 
void process_connections(int fdServer)
{
    int fd;
    int maxFD;
    int newFD;
    struct sockaddr_in fromAddr;
    int fromAddrSize;
    char buffer[1024];
    ssize_t numBytesRead;
    /* baseSet - set of file descriptors that we'll remember forever.
    ** readSet - what we copy baseSet to just before we call select().
    */
    fd_set baseSet, readSet;

    /* Max file description (only file descriptor initially is the descriptor
    ** we're listening on
    */
    maxFD = fdServer;

    /* Initialise our base set of fds, so only a 1 for the fdServer descriptor */
    FD_ZERO(&baseSet);
    FD_SET(fdServer, &baseSet);

    while(1) {
	/* Make a copy of our set of file descriptors just before we call select()
	*/
	readSet = baseSet;

	/* Block until activity occurs on one of the file descriptors in the 
	** readSet.
	*/
	if(select(maxFD + 1, &readSet, NULL, NULL, NULL) < 0) {
	    perror("Select failed");
	    exit(1);
	}
	/* If we get here, something has happened on one (or more) fds of interest
	*/
	/* Iterate over all the file descriptors of interest - go backwards */
	for(fd = maxFD; fd >= 0; fd--) {
	    /* For each file descriptor- check whether it is set in the readSet
	    ** returned to us
	    */
	    if(FD_ISSET(fd, &readSet)) {
		if(fd == fdServer) {
		    /* Listening fd - accept the connection */
		    fromAddrSize = sizeof(struct sockaddr_in);
		    newFD = accept(fdServer, (struct sockaddr*)&fromAddr,  
			      &fromAddrSize);
		    if(newFD < 0) {
			perror("Error accepting connection");
			exit(1);
		    }
		    /* Now have a new fd for a connection from a client - we need
		    ** to add it to our set of fds of interest 
		    */
		    FD_SET(newFD, &baseSet);
		    /* Update max fd if necessary */
		    if(newFD > maxFD) {
			maxFD = newFD;
		    }
		    printf("Accepted request from %s, port %d\n", 
			    inet_ntoa(fromAddr.sin_addr),
			    ntohs(fromAddr.sin_port));
		} else {
		    /* Connected client fd */
		    /* Data is available (or EOF) - so read data - we can 
		    ** guarantee this call won't be blocked 
		    */
		    numBytesRead = read(fd, buffer, 1024);
		    if(numBytesRead > 0) {
			/* Got some data - capitalise it and send it back */
			fflush(stdout);
			capitalise(buffer, numBytesRead);
			write(fd, buffer, numBytesRead);
		    } else if(numBytesRead < 0) {
			perror("Error reading from socket");
			exit(1);
		    } else {			      
			/* EOF - client has gone away.
			** Remove the fd from our set of fds of interest
			*/
			FD_CLR(fd, &baseSet);
			/* Update max FD if necessary - work backwards through
			** the set of file descriptors until we get to a fd we're
			** interested in */
			/* Code here is reason why our outer loop goes backwards
			** through the file descriptors */
			if(fd == maxFD) {
			    do {
			       maxFD--;
			    } while ( maxFD > 0 && !FD_ISSET(maxFD, &baseSet));
			}
			close(fd);
		    }
		}
	    }
	}
    }
}

 
/* Same as single process that we've seen earlier */
int main(int argc, char* argv[])
{
    int portnum;
    int fdServer;

    if(argc != 2) {
	  fprintf(stderr, "Usage: %s port-num\n", argv[0]);
	  exit(1);
    }

    portnum = atoi(argv[1]);
    if(portnum < 1024 || portnum > 65535) {
	fprintf(stderr,  "Invalid port number: %s\n", argv[1]);
	exit(1);
    }

    fdServer = open_listen(portnum);

    process_connections(fdServer);

    return 0;
}