let function_one(data) = function(){
  return new Promise( function(resolve, reject) {
    {do stuff...
      resolve('howdy');
    }
  });
};

let function_two(some_data) = function(){
  return new Promise( function(resolve, reject) {
    {  do stuff...
    resolve('howdy');
    }
  });
};

let function_three(some_data) = function(){
  return new Promise( function(resolve, reject) {
    {do stuff...
      resolve('howdy');
    }
  });
};

let function_four(some_data) = function(){
  return new Promise( function(resolve, reject) {
    {do stuff...
      resolve('howdy');
    }
  });
};

function_one(data).then(function(result){
  return function_two(result);
}).then(function(result){
  return function_three(result);
}).then(function(result){
  return function_four(result);
}).then(function(result){
  console.log(result);
}).catch(err => console.log("Caught " + err));

let gettheinformation =  function(invoicelist3){
    return new Promise(  function(resolve, reject) {
        // console.log(invoicelist3);
            Product.aggregate([
                {
                    $match: {
                        Priced: true
                    }
                }
                ,
                {
                    $group: {
                        _id: "$Invoice",
                        pricedcount: {$sum: 1}
                    }
                }
            ], function (err, result) {
                if (err) {
                    console.log(err);
                } else {
                    resolve(result);
                }
            });
    });
};


let getinvprodspriced =  function(invlist){
    return new Promise(  function(resolve, reject) {
           // console.log(invlist);
        for(var oo = 0; oo < invlist.length; oo++){
        Invoicestatus.update({Invoice:invlist[oo]._id}, {Noofitemspriced: invlist[oo].pricedcount}, {upsert: true},  function (err) {});
        }
        resolve(invlist);
        });
};

let getinvprodcount = function(invprodcount){
        return new Promise(  function(resolve, reject) {
    Product.aggregate([
                {
                    $group: {
                        _id: "$Invoice",
                        pradcount: {$sum: 1}
                    }
                }
            ], function (err, result) {
                if (err) {
                    console.log(err);
                } else {
                  // console.log(result);
                    resolve(result);
                }
            });

    });
}


let saveinvprodcount =  function(invprodcount){
    return new Promise(  function(resolve, reject) {
        for(var ok = 0; ok < invprodcount.length; ok++){
        Invoicestatus.update({Invoice:invprodcount[ok]._id}, {Noofitems: invprodcount[ok].pradcount}, {upsert: true},  function (err) {});
        }
        resolve(invprodcount);
        });
};

let getarrdocs =  function(result){
    return new Promise( function(resolve, reject) {
        Invoicestatus.find({}, function(err, docs){
          resolve(docs);
        });
    });
};

router.get('/fetcharrdata', function(req, res) {


    gettheinformation().then(function(result){
      return getinvprodspriced(result);
    }).then(function(result){
      return getinvprodcount(result);
    }).then(function(result){
      return saveinvprodcount(result);
    }).then( function(result){
      return getarrdocs(result);
    }).then(function(result){


        res.json({status: 200, data: result});


    }).catch(err => console.log("Caught " + err));

});