// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <arpa/inet.h>
#include <inet6.h>
#include <printf.h>
#include <stdint.h>
#include <string.h>

// Enable at your own risk. Some of these packet errors can be fairly
// common when the buffers start to overflow.
#if 0
#define BAD(n, ...)           \
  do {                        \
    printf("error: ");        \
    printf(n, ##__VA_ARGS__); \
    printf("\n");             \
    return;                   \
  } while (0)
#else
#define BAD(n, ...) \
  do {              \
    return;         \
  } while (0)
#endif

// useful addresses
const ip6_addr ip6_ll_all_nodes = {
    .x = {0xFF, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
};

// standard broadcast address for mDNS.
const ip6_addr ip6_mdns_broadcast = {
    .x = {0xFF, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xFB},
};

// Convert MAC Address to IPv6 Link Local Address
// aa:bb:cc:dd:ee:ff => FF80::aabb:ccFF:FEdd:eeff
// bit 2 (U/L) of the mac is inverted
static void ll6addr_from_mac(ip6_addr* _ip, const mac_addr* _mac) {
  uint8_t* ip = _ip->x;
  const uint8_t* mac = _mac->x;
  memset(ip, 0, IP6_ADDR_LEN);
  ip[0] = 0xFE;
  ip[1] = 0x80;
  memset(ip + 2, 0, 6);
  ip[8] = mac[0] ^ 2;
  ip[9] = mac[1];
  ip[10] = mac[2];
  ip[11] = 0xFF;
  ip[12] = 0xFE;
  ip[13] = mac[3];
  ip[14] = mac[4];
  ip[15] = mac[5];
}

// Convert MAC Address to IPv6 Solicit Neighbor Multicast Address
// aa:bb:cc:dd:ee:ff -> FF02::1:FFdd:eeff
static void snmaddr_from_mac(ip6_addr* _ip, const mac_addr* _mac) {
  uint8_t* ip = _ip->x;
  const uint8_t* mac = _mac->x;
  ip[0] = 0xFF;
  ip[1] = 0x02;
  memset(ip + 2, 0, 9);
  ip[11] = 0x01;
  ip[12] = 0xFF;
  ip[13] = mac[3];
  ip[14] = mac[4];
  ip[15] = mac[5];
}

// Convert IPv6 Multicast Address to Ethernet Multicast Address
static void multicast_from_ip6(mac_addr* _mac, const ip6_addr* _ip6) {
  const uint8_t* ip = _ip6->x;
  uint8_t* mac = _mac->x;
  mac[0] = 0x33;
  mac[1] = 0x33;
  mac[2] = ip[12];
  mac[3] = ip[13];
  mac[4] = ip[14];
  mac[5] = ip[15];
}

// ip6 stack configuration
mac_addr ll_mac_addr;
ip6_addr ll_ip6_addr;
mac_addr snm_mac_addr;
ip6_addr snm_ip6_addr;

// cache for the last source addresses we've seen
static mac_addr rx_mac_addr;
static ip6_addr rx_ip6_addr;

void ip6_init(void* macaddr) {
  char tmp[IP6TOAMAX];
  mac_addr all;

  // save our ethernet MAC and synthesize link layer addresses
  memcpy(&ll_mac_addr, macaddr, 6);
  ll6addr_from_mac(&ll_ip6_addr, &ll_mac_addr);
  snmaddr_from_mac(&snm_ip6_addr, &ll_mac_addr);
  multicast_from_ip6(&snm_mac_addr, &snm_ip6_addr);

  eth_add_mcast_filter(&snm_mac_addr);

  multicast_from_ip6(&all, &ip6_ll_all_nodes);
  eth_add_mcast_filter(&all);

  printf("macaddr: %02x:%02x:%02x:%02x:%02x:%02x\n", ll_mac_addr.x[0], ll_mac_addr.x[1],
         ll_mac_addr.x[2], ll_mac_addr.x[3], ll_mac_addr.x[4], ll_mac_addr.x[5]);
  printf("ip6addr: %s\n", ip6toa(tmp, &ll_ip6_addr));
  printf("snmaddr: %s\n", ip6toa(tmp, &snm_ip6_addr));
}

static int resolve_ip6(mac_addr* _mac, const ip6_addr* _ip) {
  const uint8_t* ip = _ip->x;

  // Multicast addresses are a simple transform
  if (ip[0] == 0xFF) {
    multicast_from_ip6(_mac, _ip);
    return 0;
  }

  // Trying to send to the IP that we last received a packet from?
  // Assume their mac address has not changed
  if (memcmp(_ip, &rx_ip6_addr, sizeof(rx_ip6_addr)) == 0) {
    memcpy(_mac, &rx_mac_addr, sizeof(rx_mac_addr));
    return 0;
  }

  // We don't know how to find peers or routers yet, so give up...
  return -1;
}

static uint16_t checksum(const void* _data, size_t len, uint16_t _sum) {
  uint32_t sum = _sum;
  const uint16_t* data = _data;
  while (len > 1) {
    sum += *data++;
    len -= 2;
  }
  if (len) {
    sum += (*data & 0xFF);
  }
  while (sum > 0xFFFF) {
    sum = (sum & 0xFFFF) + (sum >> 16);
  }
  return (uint16_t)sum;
}

typedef struct {
  uint8_t eth[16];
  ip6_hdr ip6;
  uint8_t data[0];
} ip6_pkt;

typedef struct {
  uint8_t eth[16];
  ip6_hdr ip6;
  udp_hdr udp;
  uint8_t data[0];
} udp_pkt;

static uint16_t ip6_checksum(ip6_hdr* ip, unsigned type, size_t length) {
  uint16_t sum;

  // length and protocol field for pseudo-header
  sum = checksum(&ip->length, 2, htons((uint16_t)type));
  // src/dst for pseudo-header + payload
  sum = checksum(ip->src, 32 + length, sum);

  // 0 is illegal, so 0xffff remains 0xffff
  return (sum != 0xFFFF) ? ~sum : sum;
}

static int ip6_setup(ip6_pkt* p, const ip6_addr* daddr, size_t length, uint8_t type) {
  mac_addr dmac;

  if (resolve_ip6(&dmac, daddr))
    return -1;

  // ethernet header
  memcpy(p->eth + 2, &dmac, ETH_ADDR_LEN);
  memcpy(p->eth + 8, &ll_mac_addr, ETH_ADDR_LEN);
  p->eth[14] = (ETH_IP6 >> 8) & 0xFF;
  p->eth[15] = ETH_IP6 & 0xFF;

  // ip6 header
  p->ip6.ver_tc_flow = 0x60;  // v=6, tc=0, flow=0
  p->ip6.length = htons((uint16_t)length);
  p->ip6.next_header = type;
  p->ip6.hop_limit = 255;
  memcpy(p->ip6.src, &ll_ip6_addr, sizeof(ip6_addr));
  memcpy(p->ip6.dst, daddr, sizeof(ip6_addr));

  return 0;
}

int udp6_send(const void* data, size_t dlen, const ip6_addr* daddr, uint16_t dport,
              uint16_t sport) {
  size_t length = dlen + UDP_HDR_LEN;
  udp_pkt* p = eth_get_buffer(ETH_MTU + 2);

  if (p == NULL)
    return -1;
  if (dlen > UDP6_MAX_PAYLOAD) {
    printf("Internal error: UDP write request is too long\n");
    goto fail;
  }
  if (ip6_setup((void*)p, daddr, length, HDR_UDP)) {
    printf("Error: ip6_setup failed!\n");
    goto fail;
  }

  // udp header
  p->udp.src_port = htons(sport);
  p->udp.dst_port = htons(dport);
  p->udp.length = htons((uint16_t)length);
  p->udp.checksum = 0;

  memcpy(p->data, data, dlen);
  p->udp.checksum = ip6_checksum(&p->ip6, HDR_UDP, length);
  return eth_send(p->eth + 2, ETH_HDR_LEN + IP6_HDR_LEN + length);

fail:
  eth_put_buffer(p);
  return -1;
}

#define ICMP6_MAX_PAYLOAD (ETH_MTU - ETH_HDR_LEN - IP6_HDR_LEN)

static uint16_t shift_combine(uint16_t x, uint16_t y) { return (uint16_t)(x << 8) | y; }

char* ip6toa(char* _out, void* ip6addr) {
  const uint8_t* x = ip6addr;
  const uint8_t* end = x + 16;
  char* out = _out;
  uint16_t n;

  n = shift_combine(x[0], x[1]);
  while ((n == 0) && (x < end)) {
    x += 2;
    n = shift_combine(x[0], x[1]);
  }

  if ((end - x) < 16) {
    if (end == x) {
      // all 0s - special case
      sprintf(out, "::");
      return _out;
    }
    // we consumed some number of leading 0s
    out += sprintf(out, ":");
    while (x < end) {
      out += sprintf(out, ":%x", n);
      x += 2;
      n = shift_combine(x[0], x[1]);
    }
    return _out;
  }

  while (x < (end - 2)) {
    out += sprintf(out, "%x:", n);
    x += 2;
    n = shift_combine(x[0], x[1]);
    if (n == 0)
      goto middle_zeros;
  }
  out += sprintf(out, "%x", n);
  return _out;

middle_zeros:
  while ((n == 0) && (x < end)) {
    x += 2;
    n = shift_combine(x[0], x[1]);
  }
  if (x == end) {
    out += sprintf(out, ":");
    return _out;
  }
  out += sprintf(out, ":%x", n);
  while (x < (end - 2)) {
    x += 2;
    n = shift_combine(x[0], x[1]);
    out += sprintf(out, ":%x", n);
  }
  return _out;
}