#include <assert.h>
#include <errno.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <time.h>
#include <unistd.h>

#include <uuid/uuid.h>

#include "cosmopolite.h"

#define COSMO_CHECK_SECONDS 10

#define min(a, b) ((a) < (b) ? (a) : (b))
#define max(a, b) ((a) > (b) ? (a) : (b))

#define DELAY_MIN_MS 250
#define DELAY_MAX_MS 32000
#define DELAY_EXPONENT 1.1
#define DELAY_STAGGER_FACTOR 10

typedef struct {
  char *send_buf;
  size_t send_buf_len;

  char *recv_buf;
  size_t recv_buf_len;

  int64_t retry_after;
} cosmo_transfer;

static size_t cosmo_read_callback(void *ptr, size_t size, size_t nmemb, void *userp) {
  cosmo_transfer *transfer = userp;
  size_t to_write = min(transfer->send_buf_len, size * nmemb);
  memcpy(ptr, transfer->send_buf, to_write);
  transfer->send_buf += to_write;
  transfer->send_buf_len -= to_write;
  return to_write;
}

static size_t cosmo_write_callback(void *ptr, size_t size, size_t nmemb, void *userp) {
  cosmo_transfer *transfer = userp;
  size_t to_read = size * nmemb;
  transfer->recv_buf = realloc(transfer->recv_buf, transfer->recv_buf_len + to_read + 1);
  assert(transfer->recv_buf);
  memcpy(transfer->recv_buf + transfer->recv_buf_len, ptr, to_read);
  transfer->recv_buf_len += to_read;
  transfer->recv_buf[transfer->recv_buf_len] = '\0';
  return to_read;
}

static size_t cosmo_header_callback(char *ptr, size_t size, size_t nmemb, void *userp) {
  cosmo_transfer *transfer = userp;
  size_t length = size * nmemb;
#define RETRY_AFTER_HEADER "Retry-After: 0\r\n"
#define RETRY_AFTER_HEADER_SIZE (sizeof(RETRY_AFTER_HEADER) - 1)
  if (length == RETRY_AFTER_HEADER_SIZE &&
      strncasecmp(ptr, RETRY_AFTER_HEADER, RETRY_AFTER_HEADER_SIZE) == 0) {
    transfer->retry_after = 0;
  }
  return length;
}

static char *cosmo_build_rpc(cosmo *instance, json_t *commands) {
  json_t *to_send = json_pack("{sssssO}", "client_id", instance->client_id, "instance_id", instance->instance_id, "commands", commands);
  assert(to_send);
  char *ret = json_dumps(to_send, 0);
  assert(ret);
  json_decref(to_send);
  return ret;
}

static bool cosmo_send_http_int(cosmo *instance, cosmo_transfer *transfer) {
  CURLcode res;
 
  curl_easy_setopt(instance->curl, CURLOPT_POST, 1L);
  curl_easy_setopt(instance->curl, CURLOPT_POSTFIELDSIZE, transfer->send_buf_len);
  curl_easy_setopt(instance->curl, CURLOPT_READFUNCTION, cosmo_read_callback);
  curl_easy_setopt(instance->curl, CURLOPT_READDATA, transfer);
  curl_easy_setopt(instance->curl, CURLOPT_WRITEFUNCTION, cosmo_write_callback);
  curl_easy_setopt(instance->curl, CURLOPT_WRITEDATA, transfer);
  curl_easy_setopt(instance->curl, CURLOPT_HEADERFUNCTION, cosmo_header_callback);
  curl_easy_setopt(instance->curl, CURLOPT_HEADERDATA, transfer);
  res = curl_easy_perform(instance->curl);

  if (res != CURLE_OK) {
    fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
    return false;
  }

  long return_code;
  assert(curl_easy_getinfo(instance->curl, CURLINFO_RESPONSE_CODE, &return_code) == CURLE_OK);
  if (return_code != 200) {
    fprintf(stderr, "server returned error: %ld\n", return_code);
    return false;
  }

  return true;
}

// Takes ownership of request.
static char *cosmo_send_http(cosmo *instance, char *request) {
  cosmo_transfer transfer = {
    .send_buf = request,
    .send_buf_len = strlen(request),
    .recv_buf = NULL,
    .recv_buf_len = 0,
    .retry_after = -1
  };

  int ret = cosmo_send_http_int(instance, &transfer);

  if (transfer.retry_after >= 0) {
    instance->next_delay_ms = transfer.retry_after * 1000;
  }

  free(request);

  return ret ? transfer.recv_buf : NULL;
}

// Takes ownership of commands.
static json_t *cosmo_send_rpc(cosmo *instance, json_t *commands) {
  char *request = cosmo_build_rpc(instance, commands);

  char *response = cosmo_send_http(instance, request);
  if (!response) {
    return commands;
  }

  json_error_t error;
  json_t *received = json_loads(response, 0, &error);
  if (!received) {
    fprintf(stderr, "json_loads() failed: %s (json: \"%s\")\n", error.text, response);
    free(response);
    return commands;
  }
  printf("response: %s\n", response);
  free(response);

  json_t *command_responses = json_object_get(received, "responses");
  if (!command_responses) {
    fprintf(stderr, "response lacks \"responses\" key\n");
    return commands;
  }

  json_t *to_retry = json_array();
  size_t index;
  json_t *command;
  json_array_foreach(commands, index, command) {
    json_t *command_response = json_array_get(command_responses, index);
    json_t *result = json_object_get(command_response, "result");
    if (!result) {
      fprintf(stderr, "response lacks \"result\" key\n");
      json_array_append(to_retry, command);
      continue;
    }
    if (!strcmp(json_string_value(result), "retry")) {
      json_array_append(to_retry, command);
      continue;
    }
    // Other result code.
  }

  json_decref(commands);
  json_decref(received);

  return to_retry;
}

static void *cosmo_thread_main(void *arg) {
  cosmo *instance = arg;

  assert(!pthread_mutex_lock(&instance->lock));
  while (!instance->shutdown) {
    if (json_array_size(instance->command_queue)) {
      json_t *commands = instance->command_queue;
      instance->command_queue = json_array();
      instance->next_delay_ms = pow(instance->next_delay_ms, DELAY_EXPONENT);
      instance->next_delay_ms = min(DELAY_MAX_MS, max(DELAY_MIN_MS, instance->next_delay_ms));
      instance->next_delay_ms += random() % (instance->next_delay_ms / DELAY_STAGGER_FACTOR);

      assert(!pthread_mutex_unlock(&instance->lock));
      json_t *to_retry = cosmo_send_rpc(instance, commands);
      assert(!pthread_mutex_lock(&instance->lock));

      json_array_extend(instance->command_queue, to_retry);
      json_decref(to_retry);
    }

    if (json_array_size(instance->command_queue)) {
      struct timeval tv;
      assert(!gettimeofday(&tv, NULL));

      struct timespec ts;
      if (tv.tv_usec + ((instance->next_delay_ms % 1000) * 1000) > 1000000) {
        // Carry
        ts.tv_sec = tv.tv_sec + (instance->next_delay_ms / 1000) + 1;
        ts.tv_nsec = (tv.tv_usec * 1000) + ((instance->next_delay_ms % 1000) * 1000000) - 1000000000;
      } else {
        ts.tv_sec = tv.tv_sec + (instance->next_delay_ms / 1000);
      }

      int wait = pthread_cond_timedwait(&instance->cond, &instance->lock, &ts);
      assert(wait == 0 || wait == ETIMEDOUT);
    } else {
      assert(!pthread_cond_wait(&instance->cond, &instance->lock));
    }
  }
  assert(!pthread_mutex_unlock(&instance->lock));
  return NULL;
}

// Takes ownership of command.
static void cosmo_send_command(cosmo *instance, json_t *command) {
  assert(command);
  assert(!pthread_mutex_lock(&instance->lock));
  json_array_append_new(instance->command_queue, command);
  instance->next_delay_ms = 0;
  assert(!pthread_cond_signal(&instance->cond));
  assert(!pthread_mutex_unlock(&instance->lock));
}

// Takes ownership of arguments.
static json_t *cosmo_command(char *name, json_t *arguments) {
  return json_pack("{ssso}", "command", name, "arguments", arguments);
}


// Public interface below

void cosmo_generate_uuid(char *uuid) {
  uuid_t uu;
  uuid_generate(uu);
  uuid_unparse_lower(uu, uuid);
}

json_t *cosmo_subject(const char *name, const char *readable_only_by, const char *writeable_only_by) {
  json_t *ret = json_pack("{ss}", "name", name);
  if (readable_only_by) {
    json_object_set_new(ret, "readable_only_by", json_string(readable_only_by));
  }
  if (writeable_only_by) {
    json_object_set_new(ret, "writeable_only_by", json_string(writeable_only_by));
  }
  return ret;
}

void cosmo_subscribe(cosmo *instance, const json_t *subject, const json_int_t messages, const json_int_t last_id) {
  json_t *arguments = json_pack("{sO}", "subject", subject);
  if (messages) {
    json_object_set_new(arguments, "messages", json_integer(messages));
  }
  if (last_id) {
    json_object_set_new(arguments, "last_id", json_integer(last_id));
  }
  cosmo_send_command(instance, cosmo_command("subscribe", arguments));
}

cosmo *cosmo_create(const char *base_url, const char *client_id) {
  curl_global_init(CURL_GLOBAL_DEFAULT);
  srandomdev();

  cosmo *instance = malloc(sizeof(cosmo));
  assert(instance);

  strcpy(instance->client_id, client_id);
  cosmo_generate_uuid(instance->instance_id);

  assert(!pthread_mutex_init(&instance->lock, NULL));
  assert(!pthread_cond_init(&instance->cond, NULL));

  instance->curl = curl_easy_init();
  assert(instance->curl);
  char api_url[strlen(base_url) + 5];
  sprintf(api_url, "%s/api", base_url);
  curl_easy_setopt(instance->curl, CURLOPT_URL, api_url);
  curl_easy_setopt(instance->curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
  curl_easy_setopt(instance->curl, CURLOPT_REDIR_PROTOCOLS, CURLPROTO_HTTPS);
  curl_easy_setopt(instance->curl, CURLOPT_SSL_CIPHER_LIST, "ECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH");
  curl_easy_setopt(instance->curl, CURLOPT_TIMEOUT, COSMO_CHECK_SECONDS);

  instance->shutdown = false;
  instance->command_queue = json_array();

  assert(!pthread_create(&instance->thread, NULL, cosmo_thread_main, instance));
  return instance;
}

void cosmo_destroy(cosmo *instance) {
  pthread_mutex_lock(&instance->lock);
  instance->shutdown = 1;
  instance->next_delay_ms = 0;
  pthread_cond_signal(&instance->cond);
  pthread_mutex_unlock(&instance->lock);
  assert(!pthread_join(instance->thread, NULL));

  assert(!pthread_mutex_destroy(&instance->lock));
  assert(!pthread_cond_destroy(&instance->cond));
  json_decref(instance->command_queue);
  curl_easy_cleanup(instance->curl);

  free(instance);

  curl_global_cleanup();
}


int main(int argc, char *argv[]) {
  char client_id[COSMO_UUID_SIZE];
  cosmo_generate_uuid(client_id);
  cosmo *instance = cosmo_create("https://playground.cosmopolite.org/cosmopolite", client_id);
  json_t *subject = cosmo_subject("foobar", NULL, NULL);
  cosmo_subscribe(instance, subject, -1, 0);
  json_decref(subject);
  sleep(120);
  cosmo_destroy(instance);

  return 0;
}