// x-run: ~/scripts/runc.sh % -lmongoose -Wall -Wextra
#include <mongoose.h>
#include <netinet/in.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

#define MAX_CLIENTS 256
#define MAX_OPEN_CHANNELS 128
#define MAX_PACKET_SIZE 32767

/*
```c
// ALL integers are network-endian

struct msg_info { // side: both. safe to ignore
    uint8_t code; // 0x49, 'I'
    uint16_t len;
    char msg[1024]; // $.len bytes sent
};

struct msg_res_error {
    uint8_t code; // 0x45, 'E'
    uint16_t req_id; // request ID that caused that error
    uint16_t len;
    char msg[1024]; // $.len bytes sent
};

struct msg_address { // side: server
    uint8_t code; // 0x41, 'A'
    uint8_t size;
    char name[256]; // $.size long
};

struct msg_res_success { // side: server
    uint8_t code; // 0x52, 'R'
    uint16_t req_id; // request ID we're replying to
    void *data; // packet-specific
};

struct msg_transmission { // side: server
    uint8_t code; // 0x54, 'T'
    uint16_t channel;
    uint16_t replyChannel;
    uint16_t size;
    void *data;
};

struct msg_req_open { // side: client
    uint8_t code; // 0x4f, 'O'
    uint16_t req_id; // incremental request ID
    uint16_t channel; // channel to be open
};

```
*/

struct client {
  struct mg_connection *connection;
  uint16_t open_channels[MAX_OPEN_CHANNELS];
  int next_open_channel_index;
  bool receive_all;
};

struct client clients[MAX_CLIENTS] = { 0 };

static void handle_client(struct mg_connection *connection, int event_type, void *ev_data, void *fn_data);
static void on_ws_connect(struct mg_connection *connection, struct mg_http_message *message, void *data);
static void on_ws_message(struct mg_connection *connection, struct mg_ws_message *message, void *data);
static void on_ws_disconnect(struct mg_connection *connection, void *data);

bool client_is_open(struct client *client, uint16_t channel);
static void modem_open(struct client *client, uint16_t request_id, uint16_t channel);
static void modem_isOpen(struct client *client, uint16_t request_id, uint16_t channel);
static void modem_close(struct client *client, uint16_t request_id, uint16_t channel);
static void modem_closeAll(struct client *client, uint16_t request_id);
static void modem_transmit(struct client *client, uint16_t request_id, uint16_t channel, uint16_t reply_channel, void *data, uint16_t size);

struct metrics {
  uint64_t sent_bytes;
  uint64_t sent_messages;
  uint64_t received_bytes;
  uint64_t received_messages;
  uint64_t errors;

  uint64_t method_calls[5];
} metrics = { 0 };

const char method_names[5][8] = {
  "open", "isOpen", "close", "closeAll", "transmit"
};

int main(void) {
  const char *address = "ws://0.0.0.0:8667";
  struct mg_mgr manager;
  mg_mgr_init(&manager);
  mg_http_listen(&manager, address, handle_client, NULL);
  printf("Listening on %s\n", address);
  while (1) mg_mgr_poll(&manager, 1000);
  mg_mgr_free(&manager);
}

static void handle_client(struct mg_connection *connection, int event_type, void *event_data, void *fn_data) {
  if (event_type == MG_EV_OPEN) {
    if (connection->rem.port == 0) return;
    memset(connection->data, 0, 32);
  } else if (event_type == MG_EV_HTTP_MSG) {
    struct mg_http_message *http_message = (struct mg_http_message *) event_data;
    if (mg_http_match_uri(http_message, "/open")) {
      mg_ws_upgrade(connection, http_message, NULL);
    } else if (mg_http_match_uri(http_message, "/metrics")) {
      mg_printf(connection, "HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n");
      mg_http_printf_chunk(connection, "# HELP ws_bytes_sent_total Number of bytes sent to clients\n");
      mg_http_printf_chunk(connection, "# TYPE ws_bytes_sent_total counter\n");
      mg_http_printf_chunk(connection, "ws_bytes_sent_total %ld\n", metrics.sent_bytes);
      mg_http_printf_chunk(connection, "# HELP ws_bytes_received_total Number of bytes received to clients\n");
      mg_http_printf_chunk(connection, "# TYPE ws_bytes_received_total counter\n");
      mg_http_printf_chunk(connection, "ws_bytes_received_total %ld\n", metrics.received_bytes);

      mg_http_printf_chunk(connection, "# HELP ws_messages_sent_total Number of messages sent to clients\n");
      mg_http_printf_chunk(connection, "# TYPE ws_messages_sent_total counter\n");
      mg_http_printf_chunk(connection, "ws_messages_sent_total %ld\n", metrics.sent_messages);
      mg_http_printf_chunk(connection, "# HELP ws_messages_received_total Number of messages received to clients\n");
      mg_http_printf_chunk(connection, "# TYPE ws_messages_received_total counter\n");
      mg_http_printf_chunk(connection, "ws_messages_received_total %ld\n", metrics.received_messages);

      mg_http_printf_chunk(connection, "# HELP ws_clients Number of active websocket clients\n");
      mg_http_printf_chunk(connection, "# TYPE ws_clients gauge\n");
      {
        int n = 0;
        for (struct mg_connection *conn = connection->mgr->conns; conn != NULL; conn = conn->next) {
          if (conn->is_websocket) { n++; }
        }
        mg_http_printf_chunk(connection, "ws_clients %d\n", n);
      }

      mg_http_printf_chunk(connection, "# HELP method_calls Times each method was called\n");
      mg_http_printf_chunk(connection, "# TYPE method_calls counter\n");
      for (int i = 0; i < 5; i++) {
        mg_http_printf_chunk(connection, "method_calls{method=\"%s\"} %ld\n", method_names[i], metrics.method_calls[i]);
      }

      mg_http_printf_chunk(connection, "");
    } else {
      mg_http_reply(connection, 404, "", "uwu");
    }
  } else if (event_type == MG_EV_WS_OPEN) {
    struct mg_http_message *http_message = (struct mg_http_message *) event_data;
    on_ws_connect(connection, http_message, fn_data);
  } else if (event_type == MG_EV_WS_MSG) {
    struct mg_ws_message *ws_message = (struct mg_ws_message *)event_data;
    on_ws_message(connection, ws_message, fn_data);
  } else if (event_type == MG_EV_CLOSE) {
    if (connection->is_websocket) {
      on_ws_disconnect(connection, fn_data);
    }
  }
}

void ws_send_error(struct client *client, uint16_t request_id, const char *fmt, ...) {
  static char buffer[1024];
  memset(buffer, 0, 1024);

  va_list args;
  va_start(args, fmt);
  int text_size = vsnprintf(&buffer[5], 1019, fmt, args);
  va_end(args);
  if (text_size < 0) return;

  buffer[0] = 'E';
  buffer[1] = (request_id >> 8) & 0xFF;
  buffer[2] = request_id & 0xFF;
  buffer[3] = (text_size >> 8) & 0xFF;
  buffer[4] = text_size & 0xFF;

  metrics.sent_bytes += 5 + text_size;
  metrics.sent_messages++;
  metrics.errors++;
  mg_ws_send(client->connection, buffer, 5 + text_size, WEBSOCKET_OP_BINARY);
}

void ws_send_info(struct client *client, const char *fmt, ...) {
  static char buffer[1024];
  memset(buffer, 0, 1024);

  va_list args;
  va_start(args, fmt);
  int text_size = vsnprintf(&buffer[3], 1021, fmt, args);
  va_end(args);
  if (text_size < 0) return;

  buffer[0] = 'I';
  buffer[1] = (text_size >> 8) & 0xFF;
  buffer[2] = text_size & 0xFF;

  metrics.sent_bytes += 3 + text_size;
  metrics.sent_messages++;
  mg_ws_send(client->connection, buffer, 3 + text_size, WEBSOCKET_OP_BINARY);
}

void ws_respond(struct client *client, uint16_t request_id, void *data, uint32_t size) {
  static char buffer[MAX_PACKET_SIZE];
  assert(size < MAX_PACKET_SIZE);
  buffer[0] = 'R';
  buffer[1] = (request_id >> 8) & 0xFF;
  buffer[2] = request_id & 0xFF;
  if (size != 0) memcpy(&buffer[3], data, size);
  metrics.sent_bytes += 3 + size;
  metrics.sent_messages++;
  mg_ws_send(client->connection, buffer, size + 3, WEBSOCKET_OP_BINARY);
}

static void on_ws_connect(struct mg_connection *connection, struct mg_http_message *message, void *data) {
  (void)message;
  (void)data;
  struct client *client = malloc(sizeof(struct client));
  memcpy(&connection->data[0], &client, sizeof(struct client *));
  client->connection = connection;

  static char buffer[256];
  buffer[0] = 'A';
  buffer[1] = snprintf(&buffer[2], 250, "wsvpn_%ld", connection->id);
  metrics.sent_bytes += 2 + buffer[1];
  metrics.sent_messages++;
  mg_ws_send(connection, buffer, 2 + buffer[1], WEBSOCKET_OP_BINARY);
}

static void on_ws_message(struct mg_connection *connection, struct mg_ws_message *message, void *data) {
  (void)data;

  if ((message->flags & 15) != WEBSOCKET_OP_BINARY) {
    const char *err_str = "This server only works in binary mode. Sorry!";
    mg_ws_send(connection, err_str, strlen(err_str), WEBSOCKET_OP_TEXT);
    connection->is_draining = 1;
    return;
  }

  struct client *client = *(struct client **)&connection->data[0];
  assert(client->connection == connection);

  metrics.received_bytes += message->data.len;
  metrics.received_messages++;

  if (message->data.len == 0) return;

  uint16_t request_id = ntohs(*(uint16_t*)&message->data.ptr[1]);

  switch (message->data.ptr[0]) {
    case 'I': // info. We can safely ignore that message
      break;
    case 'O': // open
      {
        metrics.method_calls[0]++;
        uint16_t channel = ntohs(*(uint16_t*)&message->data.ptr[3]);
        printf("%p[%04x] modem.open(%d)\n", (void*)client, request_id, channel);
        modem_open(client, request_id, channel);
      }
      return;
    case 'o': // isOpen
      {
        metrics.method_calls[1]++;
        uint16_t channel = ntohs(*(uint16_t*)&message->data.ptr[3]);
        printf("%p[%04x] modem.isOpen(%d)\n", (void*)client, request_id, channel);
        modem_isOpen(client, request_id, channel);
      }
      return;
    case 'c': // close
      {
        metrics.method_calls[2]++;
        uint16_t channel = ntohs(*(uint16_t*)&message->data.ptr[3]);
        printf("%p[%04x] modem.close(%d)\n", (void*)client, request_id, channel);
        modem_close(client, request_id, channel);
      }
      return;
    case 'C': // closeAll
      {
        metrics.method_calls[3]++;
        printf("%p[%04x] modem.closeAll()\n", (void*)client, request_id);
        modem_closeAll(client, request_id);
      }
      return;
    case 'T': // transmit
      {
        metrics.method_calls[4]++;
        uint16_t channel = ntohs(*(uint16_t*)&message->data.ptr[3]);
        uint16_t reply_channel = ntohs(*(uint16_t*)&message->data.ptr[5]);
        uint16_t data_length = ntohs(*(uint16_t*)&message->data.ptr[7]);
        modem_transmit(client, request_id, channel, reply_channel, (void*)&message->data.ptr[9], data_length);
      }
      return;
    default:
      ws_send_error(client, request_id, "Unknown opcode: 0x%02x", message->data.ptr[0]);
      connection->is_draining = 1;
      return;
  }
}

static void on_ws_disconnect(struct mg_connection *connection, void *data) {
  (void)data;

  struct client *client = *(struct client **)&connection->data[0];
  if (client->connection == connection) {
    free(client);
  }
}


static void modem_open(struct client *client, uint16_t request_id, uint16_t channel) {
  if (client_is_open(client, channel)) {
    ws_respond(client, request_id, NULL, 0);
  }

  if (client->next_open_channel_index == MAX_OPEN_CHANNELS) {
    ws_send_error(client, request_id, "Too many open channels");
    return;
  }

  client->open_channels[client->next_open_channel_index] = channel;
  client->next_open_channel_index++;
  ws_respond(client, request_id, NULL, 0);
}

static void modem_isOpen(struct client *client, uint16_t request_id, uint16_t channel) {
  unsigned char is_open = client_is_open(client, channel) ? 42 : 0;
  ws_respond(client, request_id, &is_open, 1);
}

static void modem_close(struct client *client, uint16_t request_id, uint16_t channel) {
  for (int i = 0; i < client->next_open_channel_index; i++) {
    if (client->open_channels[i] == channel) {
      client->open_channels[i] = client->open_channels[client->next_open_channel_index - 1];
      client->next_open_channel_index--;
      break;
    }
  }
  ws_respond(client, request_id, NULL, 0);
}

static void modem_closeAll(struct client *client, uint16_t request_id) {
  client->next_open_channel_index = 0;
  memset(client->open_channels, 0, sizeof(uint16_t) * MAX_OPEN_CHANNELS);
  ws_respond(client, request_id, NULL, 0);
}

static void modem_transmit(struct client *client, uint16_t request_id, uint16_t channel, uint16_t reply_channel, void *data, uint16_t size) {
  static uint8_t buffer[MAX_PACKET_SIZE + 7];

  if (size > MAX_PACKET_SIZE) {
    ws_send_error(client, request_id, "Packet too big: %d > %d", size, MAX_PACKET_SIZE);
    return;
  }

  buffer[0] = 'T';
  buffer[1] = (channel >> 8) & 0xFF;
  buffer[2] = channel & 0xFF;
  buffer[3] = (reply_channel >> 8) & 0xFF;
  buffer[4] = reply_channel & 0xFF;
  buffer[5] = (size >> 8) & 0xFF;
  buffer[6] = size & 0xFF;
  memcpy(&buffer[7], data, size);

  for (struct mg_connection *conn = client->connection->mgr->conns; conn != NULL; conn = conn->next) {
    if (conn->is_websocket) {
      struct client *other_client = *(struct client **)&conn->data[0];
      if (other_client->connection == conn && other_client->connection != client->connection) {
        if (client_is_open(other_client, channel)) {
          metrics.sent_bytes += size + 7;
          metrics.sent_messages++;
          mg_ws_send(other_client->connection, buffer, size + 7, WEBSOCKET_OP_BINARY);
        }
      }
    }
  }
  ws_respond(client, request_id, NULL, 0);
}

bool client_is_open(struct client *client, uint16_t channel) {
  for (int i = 0; i < client->next_open_channel_index; i++) {
    if (client->open_channels[i] == channel) {
      return true;
    }
  }
  return false;
}