#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

// WireGuard ---> W2U --> Internet
int main(int argc, char* argv[])
{
    int ret, flags;
    int listener, sender, ep;
    int PORT_WG=51820, PORT_ENDP=29000, PORT_UR_BEGIN=29100, PORT_UR_SIZE=10;

    while((ret = getopt(argc, argv, "hf:l:t:s:")) != -1)
    {
        switch(ret)
        {
        case 'f':
            PORT_WG=atoi(optarg);
            break;
        case 'l':
            PORT_ENDP=atoi(optarg);
            break;
        case 't':
            PORT_UR_BEGIN=atoi(optarg);
            break;
        case 's':
            PORT_UR_SIZE=atoi(optarg);
            break;
        case 'h':
        default:
            fprintf(stderr, "Usage: %s -f WGPort -l ListenPort -t TargetPort -s TargetRange\n", argv[0]);
            exit(1);
        }
    }

    fprintf(stderr, "listening on %d, receiving from %d and sending to [%d,%d)\n", PORT_ENDP, PORT_WG, PORT_UR_BEGIN, PORT_UR_BEGIN+PORT_UR_SIZE);

    listener = socket(AF_INET, SOCK_DGRAM, 0);
    struct sockaddr_in saddr;
    memset(&saddr, 0, sizeof(saddr));
    saddr.sin_family = AF_INET;
    saddr.sin_addr.s_addr = INADDR_ANY;
    saddr.sin_port = htons(PORT_ENDP);
    ret = bind(listener, (const struct sockaddr*)&saddr, sizeof(saddr));
    if (ret < 0) {
        perror("bind");
        exit(1);
    }

    sender = socket(AF_INET, SOCK_DGRAM, 0);

    // Set to non-blocking
    flags = fcntl(listener, F_GETFL, 0);
    if (flags < 0)
    {
        perror("fcntl");
        exit(1);
    }
    flags |= O_NONBLOCK;
    fcntl(listener, F_SETFL, flags);

    flags = fcntl(sender, F_GETFL, 0);
    if (flags < 0)
    {
        perror("fcntl");
        exit(1);
    }
    flags |= O_NONBLOCK;
    fcntl(sender, F_SETFL, flags);

    ep = epoll_create(1024);
    
    struct epoll_event ev1;
    ev1.events = EPOLLIN;
    ev1.data.fd = listener;

    struct epoll_event ev2;
    ev2.events = EPOLLIN;
    ev2.data.fd = sender;

    epoll_ctl(ep, EPOLL_CTL_ADD, listener, &ev1);
    epoll_ctl(ep, EPOLL_CTL_ADD, sender, &ev2);

    struct epoll_event events[1024];

    while(1)
    {
        int nfds = epoll_wait(ep, events, 1024, -1);

        if (nfds < 0) {
            perror("epoll_wait");
            break;
        }

        for (int i=0;i<nfds; i++)
        {
            if (events[i].data.fd == listener) 
            {
                struct sockaddr_in addr;
                socklen_t alen = sizeof(addr);

                char buffer[2048];
                int nsize = recvfrom(listener, &buffer, 2048, 0, (struct sockaddr*)&addr, &alen);

                if (nsize < 0) {
                    perror("recvfrom");
                } else {
                    memset(&addr, 0, sizeof(addr));
                    addr.sin_family = AF_INET;
                    inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
                    int randPort = PORT_UR_BEGIN + rand()%PORT_UR_SIZE;
                    addr.sin_port = htons(randPort);
                    sendto(sender, buffer, nsize, 0, (const struct sockaddr*)&addr, sizeof(addr));
                }
            }
            else if (events[i].data.fd == sender) 
            {
                struct sockaddr_in addr;
                socklen_t alen = sizeof(addr);

                char buffer[2048];
                int nsize = recvfrom(sender, &buffer, 2048, 0, (struct sockaddr*)&addr, &alen);

                if (nsize < 0)
                {
                    perror("recvfrom");
                }
                else
                {
                    memset(&addr, 0, sizeof(addr));
                    addr.sin_family = AF_INET;
                    inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
                    addr.sin_port = htons(PORT_WG);
                    sendto(listener, buffer, nsize, 0, (const struct sockaddr*)&addr, sizeof(addr));
                }   
            }
        }
    }
}