added googledatastore handler

/*global require,module,process*/

const datastore = require('@google-cloud/datastore');

const winston = require('winston');

class GoogleDatastoreDocumentStore {

  // Create a new store with options

  constructor(options) {

    this.kind = "Haste";

    this.expire = options.expire;

    this.datastore = new Datastore();

  }

  // Save file in a key

  set(key, data, callback, skipExpire) {

    var now = new Date();

    var expireTime = skipExpire ? null : new Date(now.getTime() + this.expire * 1000;

    var taskKey = this.datastore.key([this.kind, key])

    var task = {

      key: taskKey,

      data: [

        {

          name: 'value',

          value: data,

          excludeFromIndexes: true

        },

        {

          name: 'expiration',

          value: expireTime

        }

      ]

    };

    this.datastore.insert(task).then(() => {

      callback(true); 

    })

    .catch(err => {

      callback(false);

    });

  }

  // Get a file from a key

  get(key, callback, skipExpire) {

    var taskKey = this.datastore.key([this.kind, key])

    this.datastore.get(taskKey).then((entity) => {

      if (skipExpire) {

        callback(entity[0]["value"]);

      }

      else {

        // check for expiry

        if (entity[0]["expiration"] != null && entity[0]["expiration"] < new Date()) {

          winston.info("document expired", {key: key});

          callback(false);

        }

        else {

          // update expiry

          var now = new Date();

          var task = {

            key: taskKey,

            data: [

              {

                name: 'value',

                value: entity[0]["value"],

                excludeFromIndexes: true

              },

              {

                name: 'expiration',

                value: new Date(now.getTime() + this.expire * 1000;

              }

            ]

          };

          this.datastore.update(task).then(() => {

          })

          .catch(err => {

            winston.error("failed to update expiration", {error: err});

          });

          callback(entity[0]["value"]);

        }

      }

    })

    .catch(err => {

        winston.error("Error retrieving value from Google Datastore", {error: err});

        callback(false);

    });

}

module.exports = GoogleDatastoreDocumentStore;