Solving a puzzle with async depth-first traversal.

curb.js

var request = require('request');
var Promise = require('bluebird');
var authorize = require('./session-keys');

var BASE_URL = 'http://challenge.shopcurbside.com/';

var fetch = function(resource, session) {
  var options = {
    url: BASE_URL + resource,
    headers: { 'Session': session }
  };
  return new Promise(function(resolve, reject) {
    request(options, function(err, res, body) {
      resolve(JSON.parse(body || []));
    });
  }); 
};

var Tree = function(id) {
  this.id = id;
  this.value = null;
  this.children = [];
};

var stack = 0;

// `node` is the JSON object from Curbside
// `mirror` represents that node on the local sync tree
var traverse = function(node, mirror) {
  mirror.value = node.secret || null; 
  var clues = node.next || node.nExt || node.neXT || [];
  if (typeof clues === 'string') { clues = [clues]; }
  clues.forEach(function(clue) {
    var child = new Tree(clue);
    mirror.children.push(child);
    stack++;
    authorize()
      .then(function(session) {
        return fetch(clue, session);
      })
      .then(function(node) {
        stack--;
        traverse(node, child);
        if (stack === 0) { decipher(); }
      });
  });
};

// this is a sync representation of the puzzle's data
var puzzle;

var DFT = function(node, callback) {
  for (var i = 0; i < node.children.length; i++) {
    DFT(node.children[i], callback);
  }
  callback(node);
};

// a thin wrapper for DFT so it's easier to call
// inside the async traversal when stack finishes
var decipher = function() {
  var plain = '';
  DFT(puzzle, function(node) {
    plain += node.value || '';
  });
  console.log(plain);
};

// ACTION!
authorize()
  .then(function(session){
    return fetch('start', session);
  })
  .then(function(root) {
    puzzle = new Tree(root.id);
    traverse(root, puzzle);
  });

session-keys.js

var request = require('request');
var Promise = require('bluebird');

var LIMIT = 10;
var copies = Array.apply(null, Array(LIMIT));
var BASE_URL = 'http://challenge.shopcurbside.com/';
var url = BASE_URL + 'get-session';

var pool = [];

module.exports = function() {
  return new Promise(function(resolve, reject) {
    if (pool.length) {
      resolve(pool.shift());
    } else {
      request({ url: url }, function(err, res, body) {
        if (!body) { err = 'No data returned.'; }
        if (err) {
          reject(err);
        } else {
          pool = copies.map(function(){ return body; });
          resolve(pool.shift());
        }
      });
    }
  });
};