#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
/* #include <stdatomic.h>
#include <time.h>
#include <pthread.h> */

#define PORT 6008
#define BACKLOG 16
#define RECV_BUF 256

int main() {
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    int opt = 1;
    setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    struct sockaddr_in addr = {0};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = INADDR_ANY;
    addr.sin_port = htons(PORT);

    bind(server_fd, (struct sockaddr *)&addr, sizeof(addr));
    listen(server_fd, BACKLOG);

    printf("listening port %d\nbacklog %d\nrecv buffer %d\n", PORT, BACKLOG, RECV_BUF);

    char buf[RECV_BUF];
    const char *hdr = "X-Forwarded-For:";
    const size_t hdrlen = strlen(hdr);

    while(1) {
        int client = accept(server_fd, NULL, NULL);
        if (client < 0) continue;
        ssize_t r = recv(client, buf, sizeof(buf) -1, 0);
        if (r <= 0) { close(client); continue; }
        buf[r] = 0;
        //find header
        char *ip = NULL;
        for (ssize_t i = 0; i < r - (ssize_t)hdrlen; ++i) {
            if (strncasecmp(buf + i, hdr, hdrlen) == 0) {
                ip = buf + i + hdrlen;
                while (*ip == ' ' || *ip == '\t') ip++;
                break;
            }
        }
        //find end
        char *end = ip;
        if (ip) {
            while (*end && *end != '\r' && *end != '\n') end++;
            *end = 0;
        }
        
        //response
        const char *head = "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: ";
        char lenbuf[32];
        int iplen = ip ? strlen(ip) : 0;
        int len = snprintf(lenbuf, sizeof(lenbuf), "%d\r\n\r\n", iplen);

        send(client, head, strlen(head), 0);
        send(client, lenbuf, len, 0);
        if (iplen > 0) send(client, ip, iplen, 0);
        close(client);

    }
}