Generate FBI File

const fs = require('fs');

const fbiPath = 'Z:/';

new Promise( ( resolve, reject ) => {
    /* Read filenames in specified directory */
    fs.readdir( fbiPath, function( error, filenames ) {
        if ( error ) return reject( error );

        /* Filter out only csv files with old to new date */
        return resolve(
            filenames
            .map( filename => ( {
                name: filename,
                time: fs.statSync( fbiPath + '/' + filename ).mtime.getTime()
            } ) ) // get file and date
            .sort( ( a, b ) => a.time - b.time ) // sort old to new
            .filter( file => /\.csv$/i.test( file.name ) ) // filter csv file only
        );
    } );
} )
.then( files => {
    const csvs = files.map( file => {
        /* Read the content of CSV file */
        return fs.readFileSync( fbiPath + '/' + file.name, 'utf8' ).split( '\n' );
    } );

    /* Content arrays */
    return Promise.resolve( csvs );
} )
.then( csvs => {
    /**
     * Mergge all CSV to one
     * .reduce() is for summation of all elements in array
     */    
    const csv = csvs.reduce( ( previousValue, currentValue ) => {
        /* Check if the first column is really a column name */
        if( currentValue[0].includes( 'membership_id' ) )
            previousValue['column'] = currentValue.shift(); // Push the column name in the top of the array

        /* Push each item to column row */
        currentValue.forEach( ( value, key ) => {
            /* Get the column id */
            var id = String( value.split( ',' )[0] );

            /* If the id is not empty Insert value */
            if( id != '' )
                previousValue[id] = value; // Can be overriden the existing value with the updated one
        } );

        return previousValue;
    }, {} ); // Set the initial previousValue as empty object

    return csv
} )
.then( csv => {
    /**
     * Convert JSON Object to CSV Format
     */
    var csvFormat = [];

    /* Create flag for array key counting */
    var i = 0;

    /* Initialize the column */
    csvFormat[i] = csv.column.replace( /(\r\n|\n|\r|")/gm, '' ); // Replace unnecessarry characters

    /* Remove columnd data */
    delete csv.column;

    /* Move now the object data in array data */
    for( var id in csv ) {
        i++;

        csvFormat[i] = csv[id].replace( /(\r\n|\n|\r|")/gm, '' );
    }

    /* Convert array to string in CSV Format */
    const data = csvFormat.join( '\n' );

    /* Write to csv file */
    return Promise.resolve( fs.writeFileSync( __dirname + '/fbi.csv', data ) );
} )
.catch( error => console.error( error.message ) );