mongodb collection it contains multi language words(swear) and this util library export this collection to excel and stream to frontend

blacklist-to-excel.js

/*
*       EXAMPLE MONGODB BLACKLIST DOCUMENT OBJECT
*       
*       {
*            _id     : <mongoId>,
*            language: <which language this word>,
*            word    : <word>
*        }
*
*       DEPENDENCIES
*
*       streamifier
*       mongoose
*       node-xlsx
*

        node-xlsx data structure
        
        [  [col1,col2,...] , [col1,col2,...] , [col1,col2,...] , [col1,col2,...] , [col1,col2,...] ]
                  ↑                 ↑                 ↑                 ↑                 ↑
                 row1              row2              row3              row4              row5


        example excel output
        
        _____ ______ ______ _____ _____  
       | tr  |  en  |  ru | de   |  ar |
       ------------------------------- |
       | piç | fuck | ... | ...  | ... |
       
*/

var mongoose = require('mongoose');
var streamifier = require('streamifier');//buffer to stream utils
var xlsx = require('node-xlsx');//excel library

var BlackList = mongoose.model('BlackList');//blacklist mongoose model

BlackList.aggregate([
  {
    $group: {
      '_id': {language: '$language'},
      'word': {'$addToSet': '$word'},
      'counter': {$sum: 1}
    }
  },
  {
    $sort: {'counter': 1}
  }
], function (err, result) {
  if (err) {
    console.log('MONGO ERROR', err);
  } else {
    var maxSize = result[result.length - 1].counter;

    var data = [[]];
    var indexer = {};

    for (var i = 0; i < result.length; i++) {
      data[0][i] = result[i]._id.language;
      indexer[result[i]._id.language] = i;
    }

    for (var j = 0; j < maxSize; j++) {
      var row = [];
      for (var k = 0; k < result.length; k++) {
        var language = result[k]._id.language;
        if (j + 1 <= result[k].word.length) {
          row[parseInt(indexer[language])] = result[k].word[j];
        }
      }
      data[j + 1] = row;
    }

    var buffer = xlsx.build([{name: new Date().getTime().toString(), data: data}]);
    var size = buffer.length;

    res.writeHead(200, {
      'Content-Length': size,
      'Content-Type': 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
    });
    
    //stream excel to response 
    streamifier.createReadStream(buffer).pipe(res);
  }
});