mostly-adequate-ch-5.js

// Example Data
var CARS = [{
  name: 'Ferrari FF',
  horsepower: 660,
  dollar_value: 700000,
  in_stock: true,
}, {
  name: 'Spyker C12 Zagato',
  horsepower: 650,
  dollar_value: 648000,
  in_stock: false,
}, {
  name: 'Jaguar XKR-S',
  horsepower: 550,
  dollar_value: 132000,
  in_stock: false,
}, {
  name: 'Audi R8',
  horsepower: 525,
  dollar_value: 114200,
  in_stock: false,
}, {
  name: 'Aston Martin One-77',
  horsepower: 750,
  dollar_value: 1850000,
  in_stock: true,
}, {
  name: 'Pagani Huayra',
  horsepower: 700,
  dollar_value: 1300000,
  in_stock: false,
}];

// Exercise 1:
// ============
// Use _.compose() to rewrite the function below. Hint: _.prop() is curried.
var isLastInStock = function(cars) {
  var last_car = _.last(cars);
  return _.prop('in_stock', last_car);
};

console.log('X', _.prop('in_stock'));
const myIsLastInStock = _.compose(_.prop('in_stock'), _.last);
const myIsFirstInStock = _.compose(_.prop('in_stock'), _.first);

console.log('In stock:', myIsLastInStock(CARS), myIsFirstInStock(CARS));

// Exercise 2:
// ============
// Use _.compose(), _.prop() and _.head() to retrieve the name of the first car.
const nameOfFirstCar = _.compose(_.prop('name'), _.first);

console.log(nameOfFirstCar(CARS));

// Exercise 3:
// ============
// Use the helper function _average to refactor averageDollarValue as a composition.
var _average = function(xs) {
  return _.reduce(_.add, 0, xs) / xs.length;
}; // <- leave be

var averageDollarValue = function(cars) {
  var dollar_values = _.map(function(c) {
    return c.dollar_value;
  }, cars);
  return _average(dollar_values);
};

const myAvgDolVar = _.compose(_average, _.map(_.prop('dollar_value')));

console.log(myAvgDolVar(CARS));

// Exercise 4:

// ============
// Write a function: sanitizeNames() using compose that returns a list of lowercase and underscored car's names: e.g: sanitizeNames([{name: 'Ferrari FF', horsepower: 660, dollar_value: 700000, in_stock: true}]) //=> ['ferrari_ff'].

var _underscore = _.replace(/\W+/g, '_'); //<-- leave this alone and use to sanitize

const toLowerCase = str => str.toLowerCase();
var sanitizeNames = _.map(_.compose(_underscore, toLowerCase, _.prop('name')));

console.log(sanitizeNames(CARS));

// Bonus 1:
// ============
// Refactor availablePrices with compose.

var availablePrices = function(cars) {
  var available_cars = _.filter(_.prop('in_stock'), cars);
  return available_cars.map(function(x) {
    return accounting.formatMoney(x.dollar_value);
  }).join(', ');
};

const toDollarAmt = n => '$' + Number(n).toFixed(2); // this is a stand in for lib code
const myAvailablePrices = _.compose(_.map(_.compose(toDollarAmt, _.prop('dollar_value'))), _.filter('in_stock'));

console.log(myAvailablePrices(CARS));

// Bonus 2:
// ============
// Refactor to pointfree. Hint: you can use _.flip().

var fastestCar = function(cars) {
  var sorted = _.sortBy(function(car) {
    return car.horsepower;
  }, cars);
  var fastest = _.last(sorted);
  return fastest.name + ' is the fastest';
};

const append = str => str + ' is the fastest';
const myFastestCar = _.compose(append, _.prop('name'), _.last, _.sortBy('horsepower'));

console.log(myFastestCar(CARS));