Trello Challenge

hasher.js

module.exports = {

  hash: function (s) {
    var h = 7;
    var letters = "acdegilmnoprstuw";
    for (var i = 0; i < s.length; i++) {
      h = h * 37 + letters.indexOf(s[i]);
    }
    return h;
  },

  findAddedIndex: function (number) {
    for (var i = 15; i > -1; i--) {
      var thisNumber = number - i;
      if ((thisNumber % 37) == 0)
        return i;
    }
    throw new Error('Index not found for ' + number);
  },

  unhash: function (hash) {
    var val = hash;
    var letters = "acdegilmnoprstuw";
    var result = [];

    while (val > 7) {
      var addedValue = this.findAddedIndex(val);
      result.splice(0, 0, letters[addedValue]);
      val = (val - addedValue) / 37;
    }

    return result.join('');
  }

};

hasher.test.js

var assert = require('assert');
var hasher = require('./hasher');

describe('Hasher', function () {

  it('should return 680131659347 for string "leepadg"', function () {
    var actualHash = hasher.hash('leepadg');
    assert.strictEqual(actualHash, 680131659347);
  });

});

describe('Added Index finder', function () {

  it('should give index 4 for value 680131659347', function () {
    var addedIndex = hasher.findAddedIndex(680131659347);
    assert.strictEqual(addedIndex, 4);
  });

  it('should give index 2 for value 18381936739', function () {
    var addedIndex = hasher.findAddedIndex(18381936739);
    assert.strictEqual(addedIndex, 2);
  });

  it('should give index 0 for value 496809101', function () {
    var addedIndex = hasher.findAddedIndex(496809101);
    assert.strictEqual(addedIndex, 0);
  });

});

describe('Unhasher', function () {

  it('should return "leepadg" for hash 680131659347', function () {
    var actualString = hasher.unhash(680131659347);
    assert.strictEqual(actualString, 'leepadg');
  });

  it('should return "leepadg" for hash 956446786872726', function () {
    var actualString = hasher.unhash(956446786872726);
    assert.strictEqual(actualString, 'trellises');
  });

  it('should return "glacier" for hash 675202166929', function () {
    var actualString = hasher.unhash(675202166929);
    assert.strictEqual(actualString, 'glacier');
  });

});