Generate list of customers within 100km of GPS coordinates 53.3381985, -6.2592576. Program reads the full list of customers and outputs the names and user ids of matching customers (within 100km), sorted by user id (ascending).

inviteCustomers-Spec.js

var should = require('should');
var Invitations = require('./Invitations');

describe('Customers to invite to office', function () {
  var invite;
  
  beforeEach(function () {
    invite = new Invitations(53.3381985, -6.2592576);
  });
  
  describe('degrees to radians', function () {
    it('should throw an error if number is not valid', function () {
      should.throws(invite.degreesToRadians('hello'), Error);
    });
    
    it('should convert a number in degrees to radians', function () {
      var numberInDegrees = 52.986375;
      (invite.degreesToRadians(numberInDegrees)).should.be.approximately(0.9247, 0.01);
    });
  });
  
  describe('distance between two points', function () {
    it('should return the distance the reference point and supplied point', function () {
      (invite.distanceTo(52.986375, -6.043701)).should.be.approximately(41.676, 0.01);
    });
  });
  
  describe('read customer list from file', function () {
    it('should return a list of customers from a JSON file', function (done) {
      invite.readCustomerList('file.json', function (err, data) {
        should.not.exist(err);
        
        data.should.be.an.Array;
        data[0].name.should.equal('Christina McArdle');
        data[0].user_id.should.equal(12);
        done();
      });
    });
  });
  
  describe('generate list of customers to invite', function () {
    it('should return a list of customers to invite', function (done) {
      var testFile = 'file.json';
      invite.customerInviteList(testFile, function (err, list) {
        should.not.exist(err);
        
        list.should.be.an.Array;
        done();
      });
    });
  });
});

inviteCustomers.js

var fs = require('fs');
var _ = require('lodash');

var EARTH_RADIUS = 6371.01; // Earth's radius in km

var Invitations = function (baseLat, baseLon) {
  this.baseLat = baseLat;
  this.baseLon = baseLon;
};

Invitations.prototype.degreesToRadians = function (value) {
  if (!_.isNumber(value)) {
    throw new Error('Not a valid number');
  }
  
  return value * (Math.PI / 180);
};

Invitations.prototype.distanceTo = function (lat, lon) {
  var lat1 = this.degreesToRadians(this.baseLat),
    lat2 = this.degreesToRadians(lat),
    lon1 = this.degreesToRadians(this.baseLon),
    lon2 = this.degreesToRadians(lon);
    
  return Math.acos(Math.sin(lat1) * Math.sin(lat2) + 
    Math.cos(lat1) * Math.cos(lat2) * Math.cos(lon1 - lon2)) * EARTH_RADIUS;
};

Invitations.prototype.readCustomerList = function (list, callback) {
  fs.readFile(list, 'utf8', function (err, data) {
    if (err) { return callback(err); }
    
    var dataObj = JSON.parse(data);
    return callback(null, dataObj);
  });
};

Invitations.prototype.customerInviteList = function (file, callback) {
  this.readCustomerList(file, function (err, data) {
    if (err) { return callback(err); }
 
    var list = _.chain(data)
      .sortBy('user_id')
      .map(function (obj) {
        if (this.distanceTo(obj.latitude, obj.longitude) <= 100) {
          return {
            user_id: obj.user_id,
            name: obj.name
          };
        }
      })
      .compact()
      .value(); 
    
    return callback(null, list);
  });
};

module.exports = Invitations;