#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <netdb.h>

#define MAXHOSTNAMELEN 128

int open_listen(int port)
{
    int fd;
    struct sockaddr_in serverAddr;
    int optVal;

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

    /* Set socket option to allow port number to be reused immediately */
    optVal = 1;
    if(setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &optVal, sizeof(int)) < 0) {
	perror("Error setting socket option");
	exit(1);
    }

    /* Populate the address structure with the address that the server will
     * listen on
     */
    serverAddr.sin_family = AF_INET;	/* IP v4 */
    serverAddr.sin_port = htons(port);	/* port number - in network byte order */
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY); /* Any IP address for this 
                                                    ** machine */

    /* Bind fd to that address we've just created */
    if(bind(fd, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr_in)) < 0){
	perror("Error binding socket to port");
	exit(1);
    }

    /* Start listening on that socket */
    /* SOMAXCONN = max requests that we'll queue */
    if(listen(fd, SOMAXCONN) < 0) {
	perror("Error listening");
	exit(1);
    }

    return fd;
}

/* Converts buffer of characters to upper case */
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;
    struct sockaddr_in fromAddr;
    socklen_t fromAddrSize;
    int error;
    char hostname[MAXHOSTNAMELEN];
    char buffer[1024];
    ssize_t numBytesRead;

    while(1) {
	fromAddrSize = sizeof(struct sockaddr_in);
	/* Block - wait for a connection request, return connected file
	 * descriptor when connection request arrives
	 */
	fd = accept(fdServer, (struct sockaddr*)&fromAddr,  &fromAddrSize);
	if(fd < 0) {
	    perror("Error accepting connection");
	    exit(1);
	}
     
	/* Turn client IP address into a hostname */
	error = getnameinfo((struct sockaddr*)&fromAddr, fromAddrSize, hostname,
		MAXHOSTNAMELEN, NULL, 0, 0);
	if(error) {
	    fprintf(stderr, "Error getting hostname: %s\n", 
		    gai_strerror(error));
	} else {
	    printf("Accepted connection from %s (%s), port %d\n", 
		    inet_ntoa(fromAddr.sin_addr),
		    hostname,
		    ntohs(fromAddr.sin_port));
	}

	/* Repeatedly read characters from the connected fd, turn them into
	 * upper case and send them back 
	 */
	while((numBytesRead = read(fd, buffer, 1024)) > 0) {
	    capitalise(buffer, numBytesRead);
	    write(fd, buffer, numBytesRead);
	}

	if(numBytesRead < 0) {
	    perror("Error reading from socket");
	    exit(1);
	}
	printf("Done\n");
	fflush(stdout);
	/* Close server end of the connection */
	close(fd);
    }
}

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

    /* Start listening on that port */
    fdServer = open_listen(portnum);
    process_connections(fdServer);
    return 0;
}