datastore.js

const EventEmitter = require("events").EventEmitter;
const path = require('path');
const fs = require('fs');
const localdata = require('./localdata.js');
const logger = require('./logger.js');

class DataStore extends EventEmitter {
    constructor(filename) {
        super();
        var that = this;
        this.path = path.join(localdata.data_dir, filename);
        fs.access(this.path, fs.constants.R_OK | fs.constants.W_OK, (err) => {
            if(err) {
                fs.writeFile(that.path, "{}", () => {
                    startWatch();
                });
                return;
            }
            startWatch();
        });

        function startWatch() {
            fs.watch(that.path, 'utf8', (eventType, filename) => {
                logger.debug('%s changed', filename);
                that.load(function(err, filecontent) {
                    if(err) {
                        logger.error('Cannot fetch %s: %s', filename, err.message);
                        return;
                    }
                    logger.debug('%s reloaded', filename);
                    if(Object.keys(filecontent).length !== 0 || filecontent.constructor !== Object) {
                        that.emit('change', filecontent);
                    }
                });
            });
        }
    }

    load(callback = () => {}) {
        var that = this;
        fs.readFile(this.path, 'utf8', (err, data) => {
            if(err) {
                if(err.code !== 'ENOENT') {
                    logger.warn('Failed to load %s: %s', that.path, err.message);
                }
                data = "{}";
            }
            try {
                var obj = JSON.parse(data);
            }
            catch(e) {
                var obj = {};
            }
            callback(null, obj);
        });
    }

    save(obj, callback = (err) => err && logger.error('Failed to save: %s', err.message)) {
        if(typeof obj !== 'object') {
            return callback(new TypeError('Content should be an object', 'datastore.js'));
        }
        fs.writeFile(this.path, JSON.stringify(obj), 'utf8', callback);
    }
}

var exports = module.exports = DataStore;