#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <net/if.h> // For if_nametoindex

// Build with: gcc -shared -fPIC bind.c -o libbind.so -ldl
// Typedef for the original `bind()` function
typedef int (*pfn_bind_t)(int sockfd, const struct sockaddr *addr, socklen_t addrlen);

// Hardcoded adapter name for the IPv6 link-local address
#define HARDCODED_ADAPTER "enp5s0f3u1"

// Our custom `bind()` function
int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen) {
    // Get the original `bind()` function
    pfn_bind_t original_bind = (pfn_bind_t)dlsym(RTLD_NEXT, "bind");

    // Get environment variables
    const char *bind_addr_env = getenv("BIND_ADDR");
    const char *bind_addr6_env = getenv("BIND_ADDR6");

    // Handle IPv4 binding
    if (addr->sa_family == AF_INET) {
        if (!bind_addr_env) {
            fprintf(stderr, "bind(): BIND_ADDR not set, skipping IPv4 bind\n");
            return 0; // Simulate success
        }

        struct sockaddr_in new_addr;
        memcpy(&new_addr, addr, sizeof(new_addr)); // Copy the original address

        // Replace the IP address
        if (inet_pton(AF_INET, bind_addr_env, &new_addr.sin_addr) != 1) {
            fprintf(stderr, "Invalid BIND_ADDR: %s\n", bind_addr_env);
            return 0; // Simulate success even if the address is invalid
        }

        // Log the modification
        char original_ip[INET_ADDRSTRLEN];
        inet_ntop(AF_INET, &((struct sockaddr_in *)addr)->sin_addr, original_ip, INET_ADDRSTRLEN);
        fprintf(stderr, "bind(): Replacing IPv4 address %s with %s\n", original_ip, bind_addr_env);

        // Call the original `bind()` with the modified address
        return original_bind(sockfd, (struct sockaddr *)&new_addr, addrlen);
    }

    // Handle IPv6 binding
    if (addr->sa_family == AF_INET6) {
        if (!bind_addr6_env) {
            fprintf(stderr, "bind(): BIND_ADDR6 not set, skipping IPv6 bind\n");
            return 0; // Simulate success
        }

        struct sockaddr_in6 new_addr6;
        memcpy(&new_addr6, addr, sizeof(new_addr6)); // Copy the original address

        // Replace the IP address
        if (inet_pton(AF_INET6, bind_addr6_env, &new_addr6.sin6_addr) != 1) {
            fprintf(stderr, "Invalid BIND_ADDR6: %s\n", bind_addr6_env);
            return 0; // Simulate success even if the address is invalid
        }

        // Set the scope ID using the hardcoded adapter name
        new_addr6.sin6_scope_id = if_nametoindex(HARDCODED_ADAPTER);
        if (new_addr6.sin6_scope_id == 0) {
            fprintf(stderr, "bind(): Failed to get scope ID for adapter %s\n", HARDCODED_ADAPTER);
            return 0; // Simulate success even if scope ID can't be set
        }

        // Log the modification
        char original_ip6[INET6_ADDRSTRLEN];
        inet_ntop(AF_INET6, &((struct sockaddr_in6 *)addr)->sin6_addr, original_ip6, INET6_ADDRSTRLEN);
        fprintf(stderr, "bind(): Replacing IPv6 address %s with %s and scope ID %d\n",
                original_ip6, bind_addr6_env, new_addr6.sin6_scope_id);

        // Call the original `bind()` with the modified address
        return original_bind(sockfd, (struct sockaddr *)&new_addr6, addrlen);
    }

    // If it's neither IPv4 nor IPv6, call the original `bind()` as-is
    return original_bind(sockfd, addr, addrlen);
}