#ifndef EIM_NAT_H
#define EIM_NAT_H

#ifdef __cplusplus
extern "C" {
#endif


#include <stdint.h>
#include <stddef.h>

struct ETCP_CONN;

#define EIM_NAT_TABLE_SIZE   65536

#define EIM_NAT_ENTRY_FREE   0
#define EIM_NAT_ENTRY_ACTIVE 1
#define EIM_NAT_ENTRY_STATIC 2

#define IPPROTO_TCP_UINT8    6
#define IPPROTO_UDP_UINT8    17
#define IPPROTO_ICMP_UINT8   1

struct eim_nat_entry {
    uint32_t internal_ip;
    uint16_t internal_port;
    uint8_t  proto;
    uint8_t  state;
    uint64_t src_node_id;     // which node sent the original packet
    uint64_t last_seen;
    struct ETCP_CONN* src_conn; // cached connection for sendback
};

// Pure NAT engine state (no transport/TUN/ETCP fields)
struct eim_nat_ctx {
    uint32_t gateway_ip;
    uint16_t port_start;
    uint16_t port_end;
    uint16_t next_port;
    struct eim_nat_entry* table;
    size_t table_size;
    int initialized;
};

struct global_config;

int  eim_nat_init_ctx(struct eim_nat_ctx* ctx, const struct global_config* g);
void eim_nat_destroy_ctx(struct eim_nat_ctx* ctx);

int  eim_nat_egress(struct eim_nat_ctx* ctx, uint8_t* ip_data, size_t ip_len,
                     uint64_t src_node_id, struct ETCP_CONN* src_conn);
int  eim_nat_ingress(struct eim_nat_ctx* ctx, uint8_t* ip_data, size_t ip_len,
                      struct eim_nat_entry** out_entry);

int  eim_nat_add_forward(struct eim_nat_ctx* ctx, uint8_t proto,
                          uint32_t internal_ip_host, uint16_t internal_port_net,
                          uint16_t external_port);


#ifdef __cplusplus
}
#endif
#endif