controller.js

var mongoose = require('mongoose');
var Emission = require('../models/emissionModel');

/*
 * A function to calculate the emissions of a component.
 * Refer to the Emission schema for more information on the components.
 */

let find = (component, region, quantity) => {
    var sum = 0; // emissions accumulator
    return new Promise((resolve, reject) => {
        // find the component in the database
        Emission.findOne({ $or:[ { 'item': new RegExp(component, "i"), 'region': new RegExp(region, "i") }, { 'item': new RegExp(component, "i"), 'region': 'Default' }]}, (err, item) => {
            // if component is found
            if (!err && item) {
                console.log(`\nItem name: ${item.item} :: Type: ${item.itemType}`);
                // if component type is atomic return its CO2 emissions
                if (item.itemType == 'atomic') {
                    sum += (quantity * item.components[0].quantity);
                    console.log(`Emissions: ${sum} ${item.components[0].units}`);
                    resolve(sum);
                }
                // if component type is complex, recurse to find its atomic components
                else {
                    let numOfComponents = item.components.length; // number of subcomponents
                    for (let i = 0; i < numOfComponents; i++) {
                        find(item.components[i].name, region, item.components[i].quantity)
                            .then((emis) => {
                                sum += emis;
                                if (i === numOfComponents - 1) {
                                    resolve(quantity * sum);
                                }
                            })
                            .catch((err) => console.log(err));
                    }
                }
            } 
            // return an error if component is not found
            else reject(`Unable to find component ${component} for ${region}`);
        });
    });
}

exports.find = (req, res) => {
	// dummy values for testing
    find(item,region,quantity)
        .then((sum) => {
            console.log(`\nTotal Emissions: ${sum}`);
            res.json({
                success: true,
                emissions: parseFloat(sum.toFixed(10))
            });
        })
        .catch((err) => {
            console.log(`Error: ${err}`);
            res.json({
                success: false,
                err: err
            });
        });
}

router.js

var express = require('express');
var router = express.Router();
// get the emission controller
var Emission = require('../controllers/emissionController'); 

router.post('/',function (req, res) {
    // console.log(req.body);      // your JSON
    // res.send(req.body);    // echo the result back
    res.status(200).send(Emission.find('electricity','Africa',1));
})
// router.get('/', Emission.find);

module.exports = router;
//curl test- curl -H "Content-Type: application/json" -X POST -d '{"item":"electricity","region":"Africa","unit":"kg/kWh","quantity":1}' http://localhost:3080/v1/emissions