dumboDB-file-read-write.js

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

const dbFilePath = path.join(__dirname, 'db.json'); //  path to the json file where we are storing our hash data
const MAX_TRY_COUNT = 5;  //  Maximum numebr of attempts in case of failure 

let readTryCount = 0; // hold the read try count
let writeTryCount = 0; // hold the write try count

const hash = {};

//  to get the value for a particular index
const get = index => typeof hash[index] !== "undefined" ? hash[index] : null;

//  add a new value in a particular index
const set = (index, data) => {
  if( typeof hash[index] === "undefined"){
    hash[index] = [];
  }
  hash[index].push(data);
}

//  remove a value from a particular index
const pop = (index, value) => {
  if( typeof hash[index] === "undefined"){
    return true;
  }
  
  const valueIndex = hash[index].indexOf(value);
  if(valueIndex > -1){
    hash[index].splice(valueIndex, 1);
  } 
  
  commitDB(); // updating the file with latest hash content
  
  return true;
}

//  remove all values stored in a particular index
const remove = index => {
  if( typeof hash[index] !== "undefined"){
    delete hash[index];
  }
  
  commitDB(); // updating the file with latest hash content
  
  return true;
}

const readDB = () => {
  fs.readFile(dbFilePath, (err, data) => {
    if(err){
      if(readTryCount < MAX_TRY_COUNT){
        setTimeout(readDB, 1000); //  let's try again 1s later
      }
      else{
        throw err;  //  raise the error
      }
    }
    try{
      data = JSON.parse(data);
      //  hash is a constant so we can't directly assign the data
      //  we can assign properties by the way
      for (key in data) {
        hash[key] = data[key]; // copies each property to the data object
      }
      readTryCount = 0;
    }
    catch(e){
      throw e;  //  bad data?
    }

  });
}

//  commiting the changes in the file
const commitDB = () => {
  const data = JSON.stringify(hash);
  const options = {
    encoding: 'utf8'
  }; 
  
  fs.writeFile(dbFilePath, data, options, (err) => {
    if(err){
      if(writeTryCount < MAX_TRY_COUNT){
        setTimeout(commitDB, 1000); // let's try again 1s later
        writeTryCount++;
      }
      else{
        throw err; // raise the error
      }
    }
  
    // file is updated so nothing to do here...
    writeTryCount = 0;
  });
}

//  Read the file for the first time when the module loads
readDB();

//  exposing the getter and setters
exports.get = get;
exports.pop = pop;
exports.remove = remove;