const { promisify } = require('util');
const redis = require('redis');

const REDIS_URL = process.env.REDIS_URL || 'redis://localhost:6379';
const CACHE_KEY_PREFIX = process.env.REDIS_GLOBAL_CACHE_KEY_PREFIX || '';
const CACHE_TTL = process.env.REDIS_TTL || 60 * 5; // seconds
const DEFAULT_VERSION = 1;

const client = redis.createClient(REDIS_URL);
const redisGet = promisify(client.get).bind(client);
const redisSet = promisify(client.set).bind(client);
const redisDelete = promisify(client.del).bind(client);
const redisHget = promisify(client.hget).bind(client);
const redisHset = promisify(client.hset).bind(client);
const redisExists = promisify(client.exists).bind(client);

function getCacheKey({ prefix, version, key }) {
  const cachePrefix = prefix || CACHE_KEY_PREFIX;
  const cacheVersion = version || DEFAULT_VERSION;
  return `${cachePrefix}-${cacheVersion}-${key}`;
}

function serialize(value) {
  if (typeof value === 'object') {
    return JSON.stringify(value);
  }
  return value;
}

function deSerialize(cachedValue) {
  try {
    return JSON.parse(cachedValue);
  } catch (error) {
    return cachedValue;
  }
}

async function get(key, options = {}) {
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  return redisGet(cacheKey).then(result => deSerialize(result));
}

async function set(key, value, options = {}) {
  const ttl = options.ttl || CACHE_TTL;
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  const serializedValue = serialize(value);

  if (!ttl) {
    return redisSet(cacheKey, serializedValue);
  }
  return redisSet(cacheKey, serializedValue, 'EX', ttl);
}

async function del(key, options = {}) {
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  return redisDelete(cacheKey);
}

async function hget(key, field, options = {}) {
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  return redisHget(cacheKey, field);
}

async function hset(key, field, value, options = {}) {
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  return redisHset(cacheKey, field, value);
}

async function exists(key, options = {}) {
  const version = options.version || DEFAULT_VERSION;
  const cacheKey = getCacheKey({ key, version });
  return redisExists(cacheKey);
}

module.exports = {
  get,
  set,
  del,
  hget,
  hset,
  exists,
};