'use strict';

const fs = require('fs');
const path = require('path');
const v8 = require('v8');

const PATH = `${__dirname}/sessions`;

const safePath = fn => (token, ...args) => {
  const callback = args[args.length - 1];
  const fileName = path.join(PATH, token);
  if (!fileName.startsWith(PATH)) {
    callback(new Error('Invalid session token'));
    return;
  }
  fn(fileName, ...args, callback);
};

const readSession = safePath(fs.readFile);
const writeSession = safePath(fs.writeFile);
const deleteSession = safePath(fs.unlink);

class Storage extends Map {
  get(key, callback) {
    const value = super.get(key);
    if (value) {
      callback(null, value);
      return;
    }
    readSession(key, (err, data) => {
      if (err) {
        callback(err);
        return;
      }
      console.log(`Session loaded: ${key}`);
      const session = v8.deserialize(data);
      super.set(key, session);
      callback(null, session);
    });
  }

  save(key) {
    const value = super.get(key);
    const data = v8.serialize(value);
    if (value) writeSession(key, data, () => {
      console.log(`Session saved: ${key}`);
    });
  }

  delete(key) {
    deleteSession(key, () => {
      console.log(`Session deleted: ${key}`);
    });
  }
}

module.exports = new Storage();