#include <stdio.h>
#include <stdlib.h>
#include <sys/un.h>
#include <sys/socket.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <strings.h>
#include <netdb.h>
#include <signal.h>

#define DEFAULT_PORT 80
#define MAX_CONNECTIONS 20
#define PAUSE_TIME_SEC 1
#define BUFFER_SIZE 1000

extern int errno;

typedef struct sockaddr_in SocketAddress;

static volatile sig_atomic_t keep_running = 1;

static void sigHandler(int _)
{
    keep_running = 0;
}

void setupSocketAddress(SocketAddress *socketAddress, int port)
{
    socketAddress->sin_family = AF_INET;
    socketAddress->sin_addr.s_addr = htonl(INADDR_ANY);
    socketAddress->sin_port = htons(port);
}

void die(const char *message)
{
    printf("%s\n", message);
    exit(1);
}

void sendHelloMessage(int connectionFileDescriptor)
{
    // send hello message
    char helloMessage[] = "Hello from server\n";

    write(connectionFileDescriptor, helloMessage, sizeof(helloMessage));
}

void receiveFromClient(int connectionFileDescriptor)
{
    char buff[BUFFER_SIZE];

    // read from client
    bzero(buff, BUFFER_SIZE);
    read(connectionFileDescriptor, buff, sizeof(buff));

    printf("From client:\n%s\n", buff);
    printf("Sending reply from client\n");
}

void sendReplyFromServer(int connectionFileDescriptor)
{
    // send hello message
    char replyFromServer[] = "Reply from server\n";

    write(connectionFileDescriptor, replyFromServer, sizeof(replyFromServer));
}

void acceptClientMessage(int connectionFileDescriptor)
{

    sendHelloMessage(connectionFileDescriptor);

    receiveFromClient(connectionFileDescriptor);

    sendReplyFromServer(connectionFileDescriptor);
}

int main(int argc, char *argv[])
{
    int defaultPort = DEFAULT_PORT;
    SocketAddress socketAddress, cli;
    int socketFileDescriptor, socketBindOperation, socketListenOperation, connectionFileDescriptor;
    char buff[1000];
    socklen_t addrlen;
    int true = 1, forkID;

    // signal(SIGINT, sigHandler);

    if (argc > 1)
    {
        defaultPort = atoi(argv[1]);
    }

    socketFileDescriptor = socket(AF_INET, SOCK_STREAM, 0);
    if (socketFileDescriptor == -1)
    {
        die("Socket create failed");
    }
    setsockopt(socketFileDescriptor, SOL_SOCKET, SO_REUSEADDR, &true, sizeof(int));

    setupSocketAddress(&socketAddress, defaultPort);

    socketBindOperation = bind(socketFileDescriptor, (struct sockaddr *)&socketAddress, sizeof(socketAddress));
    if (socketBindOperation != 0)
    {
        printf("errno %d\n", errno);

        die("Socket bind failed...");
    }
    printf("Socket :%d binded...\n", defaultPort);

    socketListenOperation = listen(socketFileDescriptor, MAX_CONNECTIONS);
    if (socketListenOperation != 0)
    {
        die("Listen failed...\n");
    }
    printf("Server Listening...\n");

    // multiple connections
    //for (; keep_running;)
    while (keep_running)
    {
        addrlen = sizeof(cli);
        connectionFileDescriptor = accept(socketFileDescriptor, (struct sockaddr *)&cli, &addrlen);
        if (connectionFileDescriptor == -1)
        {
            die("Server accept failed...");
        }

        forkID = fork();
        // child process
        if (forkID == 0)
        {
            printf("Server accepted the client...\n");

            acceptClientMessage(connectionFileDescriptor);

            close(connectionFileDescriptor);
            printf("Server closed the connection\n");

            exit(0);
        }
        // parent process
        else{
            wait(NULL);
        }
    }
    // if it is parent
    if (forkID != 0)
    {
        close(socketFileDescriptor);

        printf("Closed %d\n", getpid());
    }
    return 0;
}