// udp_proxy.c — UDP датаграммный прокси: клиент ↔ exit через etcp_router
#include "udp_proxy.h"
#include "etcp.h"
#include "etcp_api.h"
#include "etcp_router.h"
#include "utun_instance.h"
#include "tun_if.h"
#include "../routing_layer/topo_node.h"
#include "../lib/u_async.h"
#include "../lib/debug_config.h"
#include "../lib/ll_queue.h"
#include "../lib/mem.h"
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#ifndef _WIN32
#include <unistd.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#endif

#define UDP_FLOW_TIMEOUT_TB 600000  // 60с


static void flow_expire_timer_cb(void* arg);
static void flow_expire(struct udp_proxy_ctx* ctx);

static struct udp_flow* flow_find(struct udp_flow* head, uint64_t client_node_id,
                                   uint32_t src_ip, uint16_t src_port,
                                   uint32_t dst_ip, uint16_t dst_port) {
    struct udp_flow* f;
    for (f = head; f; f = f->next)
        if (f->client_node_id == client_node_id && f->src_ip == src_ip &&
            f->src_port == src_port && f->dst_ip == dst_ip && f->dst_port == dst_port) return f;
    return NULL;
}

static void flow_read_cb(socket_t sock, void* arg) {
    (void)sock; struct udp_flow* f = (struct udp_flow*)arg;
    struct udp_proxy_ctx* ctx = f ? f->ctx : NULL;
    if (!f || f->sock == SOCKET_INVALID || !ctx) return;
    uint8_t buf[65507];
    struct sockaddr_in from; socklen_t flen = sizeof(from);
    ssize_t n = recvfrom(f->sock, buf, sizeof(buf), 0, (struct sockaddr*)&from, &flen);
    if (n < 0) { DEBUG_WARN(DEBUG_CATEGORY_PROXY, "udp_proxy: recv failed errno=%d", errno); return; }
    if (from.sin_addr.s_addr != f->dst_ip || from.sin_port != f->dst_port) {
        DEBUG_WARN(DEBUG_CATEGORY_PROXY, "udp_proxy: unexpected reply source"); return;
    }

    f->last_activity_tb = get_time_tb();

    // Обернуть ответ: меняем src/dst для восстановления на стороне клиента
    struct ll_entry* e = queue_entry_new(0);
    if (!e) return;
    e->dgram = u_malloc(UDP_PROXY_HDR_SIZE + n);
    if (!e->dgram) { queue_entry_free(e); return; }
    e->dgram[0] = ETCP_RT_ID_UDP_PROXY;
    e->dgram[1] = UDP_PROXY_SUBCMD_REPLY;
    // Ответ src = оригинальный dst_ip:dest_port
    memcpy(e->dgram + 2, &f->dst_ip, 4);
    memcpy(e->dgram + 6, &f->dst_port, 2);
    // Ответ dst = оригинальный src_ip:src_port
    memcpy(e->dgram + 8, &f->src_ip, 4);
    memcpy(e->dgram + 12, &f->src_port, 2);
    memcpy(e->dgram + UDP_PROXY_HDR_SIZE, buf, n);
    e->len = UDP_PROXY_HDR_SIZE + n;

    etcp_route_send(ctx->inst, TOPO_GROUP_UTUN, f->client_node_id, e, 0, 0);
}

// ====================================================================
// Exit узел: принять REQUEST, создать сокет, переслать
// ====================================================================
static void exit_handle_data(struct ETCP_CONN* conn, struct ll_entry* entry) {
    struct UTUN_INSTANCE* inst = conn ? conn->instance : NULL;
    struct udp_proxy_ctx* ctx = inst ? inst->udp_proxy : NULL;
    if (!inst || !ctx || !inst->tcp_proxy_server.enabled || entry->len < UDP_PROXY_RECV_HDR_SIZE) goto drop;

    uint64_t client_node_id; memcpy(&client_node_id, entry->dgram + ROUTER_SVC_SRC_OFF, 8);
    uint32_t src_ip;  memcpy(&src_ip,  entry->dgram + ROUTER_SVC_PAYLOAD_OFF + 1, 4);
    uint16_t src_port; memcpy(&src_port, entry->dgram + ROUTER_SVC_PAYLOAD_OFF + 5, 2);
    uint32_t dst_ip;  memcpy(&dst_ip,  entry->dgram + ROUTER_SVC_PAYLOAD_OFF + 7, 4);
    uint16_t dst_port; memcpy(&dst_port, entry->dgram + ROUTER_SVC_PAYLOAD_OFF + 11, 2);
    uint8_t* payload = entry->dgram + UDP_PROXY_RECV_HDR_SIZE;
    size_t payload_len = entry->len - UDP_PROXY_RECV_HDR_SIZE;

    struct udp_flow* f = flow_find(ctx->flows, client_node_id, src_ip, src_port, dst_ip, dst_port);
    if (!f) {
        f = u_calloc(1, sizeof(struct udp_flow));
        if (!f) goto drop;
        f->ctx = ctx;
        f->client_node_id = client_node_id; f->src_ip = src_ip; f->src_port = src_port;
        f->dst_ip = dst_ip; f->dst_port = dst_port;
        f->ua = ctx->ua; f->created_tb = get_time_tb(); f->last_activity_tb = f->created_tb;

        f->sock = socket(AF_INET, SOCK_DGRAM, 0);
        if (f->sock == SOCKET_INVALID) { u_free(f); DEBUG_ERROR(DEBUG_CATEGORY_PROXY, "udp_proxy: socket failed"); goto drop; }
        socket_set_nonblocking(f->sock);
        struct sockaddr_in bind_addr = {.sin_family = AF_INET, .sin_addr = {.s_addr = INADDR_ANY}, .sin_port = 0};
        bind(f->sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr));
        f->read_id = uasync_add_socket_t(ctx->ua, f->sock, flow_read_cb, NULL, NULL, "udp_flow", f);
        if (!f->read_id) { socket_close_wrapper(f->sock); u_free(f); goto drop; }
        f->next = ctx->flows; ctx->flows = f; ctx->flow_count++;
        if (!ctx->expire_timer)
            ctx->expire_timer = uasync_set_timeout(ctx->ua, ctx->flow_timeout_tb, ctx, flow_expire_timer_cb, "udp_expire");
    }
    f->last_activity_tb = get_time_tb();

    struct sockaddr_in addr = {.sin_family = AF_INET, .sin_addr = {.s_addr = dst_ip}, .sin_port = dst_port};
    sendto(f->sock, payload, payload_len, 0, (struct sockaddr*)&addr, sizeof(addr));

drop:
    queue_dgram_free(entry); queue_entry_free(entry);
}

// ====================================================================
// Сторона клиента: принять REPLY, доставить в TUN
// ====================================================================
static void client_handle_reply(struct ETCP_CONN* conn, struct ll_entry* entry) {
    if (entry->len < UDP_PROXY_RECV_HDR_SIZE) { queue_dgram_free(entry); queue_entry_free(entry); return; }
    const uint8_t* d = entry->dgram;
    uint32_t src_ip, dst_ip;
    uint16_t src_port, dst_port;
    // В сообщении: src_ip:src_port = оригинальный dst, dst_ip:dst_port = оригинальный src
    memcpy(&src_ip,   d + ROUTER_SVC_PAYLOAD_OFF + 1, 4);
    memcpy(&src_port, d + ROUTER_SVC_PAYLOAD_OFF + 5, 2);
    memcpy(&dst_ip,   d + ROUTER_SVC_PAYLOAD_OFF + 7, 4);
    memcpy(&dst_port, d + ROUTER_SVC_PAYLOAD_OFF + 11, 2);
    uint8_t* payload = d + UDP_PROXY_RECV_HDR_SIZE;
    size_t payload_len = entry->len - UDP_PROXY_RECV_HDR_SIZE;

    struct UTUN_INSTANCE* inst = conn ? conn->instance : NULL;
    udp_proxy_deliver_reply(inst, src_ip, src_port, dst_ip, dst_port, payload, payload_len);
    queue_dgram_free(entry); queue_entry_free(entry);
}

// ====================================================================
// Единый etcp_router коллбэк
// ====================================================================
void udp_proxy_recv_cb(struct ETCP_CONN* conn, struct ll_entry* entry) {
    if (!entry || !entry->dgram || entry->len <= ROUTER_SVC_HDR_SIZE) {
        if (entry) { queue_dgram_free(entry); queue_entry_free(entry); }
        return;
    }
    struct UTUN_INSTANCE* inst = conn ? conn->instance : NULL;
    uint64_t peer; memcpy(&peer, entry->dgram + ROUTER_SVC_SRC_OFF, 8);
    uint8_t subcmd = entry->dgram[ROUTER_SVC_PAYLOAD_OFF];
    if (subcmd == UDP_PROXY_SUBCMD_REQUEST && inst && inst->tcp_proxy_server.enabled) {
        exit_handle_data(conn, entry); return;
    }
    if (subcmd == UDP_PROXY_SUBCMD_REPLY && inst && inst->tcp_proxy_client && peer == inst->tcp_proxy_client->via_node_id) {
        client_handle_reply(conn, entry); return;
    }
    DEBUG_WARN(DEBUG_CATEGORY_PROXY, "udp_proxy: rejected subcmd=%u peer=%016llx", subcmd, (unsigned long long)peer);
    queue_dgram_free(entry); queue_entry_free(entry);
}

// ====================================================================
// Сторона клиента: отправить UDP датаграмму в exit узел
// ====================================================================
int udp_proxy_send_to_exit(struct UTUN_INSTANCE* inst, uint64_t exit_node_id,
                           uint32_t src_ip, uint16_t src_port,
                           uint32_t dst_ip, uint16_t dst_port,
                           const uint8_t* payload, size_t payload_len) {
    if (!inst || !inst->udp_proxy || payload_len > 65507) { DEBUG_WARN(DEBUG_CATEGORY_PROXY, "udp_proxy: invalid send"); return -1; }
    struct ll_entry* e = queue_entry_new(0);
    if (!e) return -1;
    e->dgram = u_malloc(UDP_PROXY_HDR_SIZE + payload_len);
    if (!e->dgram) { queue_entry_free(e); return -1; }
    e->dgram[0] = ETCP_RT_ID_UDP_PROXY;
    e->dgram[1] = UDP_PROXY_SUBCMD_REQUEST;
    memcpy(e->dgram + 2, &src_ip, 4);
    memcpy(e->dgram + 6, &src_port, 2);
    memcpy(e->dgram + 8, &dst_ip, 4);
    memcpy(e->dgram + 12, &dst_port, 2);
    if (payload_len > 0) memcpy(e->dgram + UDP_PROXY_HDR_SIZE, payload, payload_len);
    e->len = UDP_PROXY_HDR_SIZE + payload_len;
    return etcp_route_send(inst, TOPO_GROUP_UTUN, exit_node_id, e, 0, 0);
}

// ====================================================================
// Сторона клиента: доставить UDP ответ в TUN
// ====================================================================
int udp_proxy_deliver_reply(struct UTUN_INSTANCE* inst,
                            uint32_t src_ip, uint16_t src_port,
                            uint32_t dst_ip, uint16_t dst_port,
                            const uint8_t* payload, size_t payload_len) {
    if (!inst || !inst->tcp_proxy_client || !inst->tcp_proxy_client->tun || payload_len > 65506) return -1;

    // Собрать IP/UDP ответный пакет
    size_t ip_len = 20 + 8 + payload_len;
    uint8_t* pkt = u_malloc(ip_len);
    if (!pkt) return -1;

    memset(pkt, 0, 28); // IPv4 UDP checksum=0: проверка отключена явно
    pkt[0] = 0x45; pkt[8] = 64; pkt[9] = IPPROTO_UDP;
    memcpy(pkt + 12, &src_ip, 4); memcpy(pkt + 16, &dst_ip, 4);

    uint16_t total_len = htons(20 + 8 + payload_len);
    memcpy(pkt + 2, &total_len, 2);

    {   uint32_t ip_sum = 0; for (int i = 0; i < 10; i++) { uint16_t w; memcpy(&w, pkt + i*2, 2); ip_sum += w; }
        ip_sum = (ip_sum & 0xFFFF) + (ip_sum >> 16); ip_sum += (ip_sum >> 16);
        uint16_t cs = (uint16_t)(~ip_sum); memcpy(pkt + 10, &cs, 2); }

    uint16_t udp_len = htons(8 + payload_len);
    memcpy(pkt + 24, &udp_len, 2);
    memcpy(pkt + 20, &src_port, 2);
    memcpy(pkt + 22, &dst_port, 2);
    if (payload_len > 0) memcpy(pkt + 28, payload, payload_len);

    struct ll_entry* e = queue_entry_new(0);
    if (!e) { u_free(pkt); return -1; }
    e->dgram = u_malloc(1 + ip_len);
    if (!e->dgram) { DEBUG_ERROR(DEBUG_CATEGORY_PROXY, "udp_proxy: reply allocation failed"); u_free(pkt); queue_entry_free(e); return -1; }
    e->dgram[0] = 4; memcpy(e->dgram + 1, pkt, ip_len); e->len = 1 + ip_len;
    u_free(pkt);
    queue_data_put(inst->tcp_proxy_client->tun->input_queue, e);
    return 0;
}

static void flow_expire_timer_cb(void* arg) {
    struct udp_proxy_ctx* ctx = (struct udp_proxy_ctx*)arg;
    flow_expire(ctx);
    ctx->expire_timer = NULL;
    if (ctx->flows)
        ctx->expire_timer = uasync_set_timeout(ctx->ua, ctx->flow_timeout_tb, ctx, flow_expire_timer_cb, "udp_expire");
}

static void flow_expire(struct udp_proxy_ctx* ctx) {
    uint64_t now = get_time_tb(); struct udp_flow** prev = &ctx->flows;
    while (*prev) {
        struct udp_flow* f = *prev;
        if (now - f->last_activity_tb > ctx->flow_timeout_tb) {
            *prev = f->next; ctx->flow_count--;
            if (f->read_id) { uasync_remove_socket_t(f->ua, f->sock); f->read_id = NULL; }
            socket_close_wrapper(f->sock); u_free(f);
        } else prev = &f->next;
    }
}

// ====================================================================
// Публичные init/destroy
// ====================================================================
int udp_proxy_init(struct UTUN_INSTANCE* inst, struct UASYNC* ua) {
    if (!inst) return -1;
    if (inst->udp_proxy) return 0;
    struct udp_proxy_ctx* ctx = u_calloc(1, sizeof(struct udp_proxy_ctx));
    if (!ctx) return -1;
    ctx->inst = inst; ctx->ua = ua;
    ctx->flow_timeout_tb = UDP_FLOW_TIMEOUT_TB;
    ctx->expire_timer = NULL;
    ctx->is_exit = inst->tcp_proxy_server.enabled;
    inst->udp_proxy = ctx;

    etcp_router_bind(inst, ETCP_RT_ID_UDP_PROXY, udp_proxy_recv_cb);
    ctx->initialized = 1;
    DEBUG_INFO(DEBUG_CATEGORY_PROXY, "udp_proxy initialized (exit=%d)", ctx->is_exit);
    return 0;
}

void udp_proxy_destroy(struct UTUN_INSTANCE* inst) {
    struct udp_proxy_ctx* ctx = inst ? inst->udp_proxy : NULL;
    if (!ctx) return;
    etcp_router_unbind(inst, ETCP_RT_ID_UDP_PROXY);
    if (ctx->expire_timer) { uasync_cancel_timeout(ctx->ua, ctx->expire_timer); ctx->expire_timer = NULL; }
    struct udp_flow* f = ctx->flows;
    while (f) { struct udp_flow* n = f->next;
        if (f->read_id) { uasync_remove_socket_t(ctx->ua, f->sock); f->read_id = NULL; }
        socket_close_wrapper(f->sock); u_free(f); f = n; }
    u_free(ctx); inst->udp_proxy = NULL;
    DEBUG_INFO(DEBUG_CATEGORY_PROXY, "udp_proxy destroyed");
}