//decorator function
const allArgsValid = function(fn) {
  return function(...args) {
  if (args.length != fn.length) {
      throw new Error('Only submit required number of params');
    }
    const validArgs = args.filter(arg => Number.isInteger(arg));
    if (validArgs.length < fn.length) {
      throw new TypeError('Argument cannot be a non-integer');
    }
    return fn(...args);
  }
}
//ordinary multiply function
let multiply = function(a,b){
  return a*b;
}
//decorated multiply function that only accepts the required number of params and only integers
multiply = allArgsValid(multiply);
multiply(6, 8);
//48
multiply(6, 8, 7);
//Error: Only submit required number of params
multiply(3, null);
//TypeError: Argument cannot be a non-integer
multiply('',4);
//TypeError: Argument cannot be a non-integer

//ordinary add function
let add = function(a,b){
  return a+b;
}
//decorated add function that only accepts the required number of params and only integers
add = allArgsValid(add);
add(6, 8);
//14
add(3, null);
//TypeError: Argument cannot be a non-integer
add('',4);
//TypeError: Argument cannot be a non-integer

function log(fn) {
  return function() {
    console.log("Execution of " + fn.name);
    console.time("fn");
    let val = fn();
    console.timeEnd("fn");
    return val;
  }
}
class Book {
  constructor(name, ISBN) {
    this.name = name;
    this.ISBN = ISBN;
  }
  getBook() {
    return `[${this.name}][${this.ISBN}]`;
  }
}
let obj = new Book("HP", "1245-533552");
let getBook = log(obj.getBook);
console.log(getBook());
//TypeError: Cannot read property 'name' of undefined

function log(classObj, fn) {
  return function() {
    console.log("Execution of " + fn.name);
    console.time("fn");
    let val = fn.call(classObj);
    console.timeEnd("fn");
    return val;
  }
}
class Book {
  constructor(name, ISBN) {
    this.name = name;
    this.ISBN = ISBN;
  }
  getBook() {
    return `[${this.name}][${this.ISBN}]`;
  }
}
let obj = new Book("HP", "1245-533552");
let getBook = log(obj, obj.getBook);
console.log(getBook());
//[HP][1245-533552]

@log

function log(target) {
  return function(...args) {
    console.log("Constructor called");
    return new target(...args);
  };
}
@log
class Book {
  constructor(name, ISBN) {
    this.name = name;
    this.ISBN = ISBN;
  }
  getBook() {
    return `[${this.name}][${this.ISBN}]`;
  }
}
let obj = new Book("HP", "1245-533552");
//Constructor Called
console.log(obj.getBook());
//HP][1245-533552]

function logWithParams(...params) {
  return function(target) {
    return function(...args) {
      console.table(params);
      return new target(...args);
    }
  }
}
@log
@logWithParams('param1', 'param2')
class Book {
  //Class implementation as before
}
let obj = new Book("HP", "1245-533552");
//Constructor called
//Params will be consoled as a table
console.log(obj.getBook());
//[HP][1245-533552]

//readonly decorator function
function readOnly(target, name, descriptor) {
  descriptor.writable = false;
  return descriptor;
}
class Book {
  //Implementation here
  @readOnly
  getBook() {
    return `[${this.name}][${this.ISBN}]`;
  }
}
let obj = new Book("HP", "1245-533552");
obj.getBook = "Hello";
console.log(obj.getBook());
//[HP][1245-533552]

obj.getBook = "Hello";
console.log(obj.getBook);
//Hello

function upperCase(target, name, descriptor) {
  if (descriptor.initializer && descriptor.initializer()) {
    let val = descriptor.initializer();
    descriptor.initializer = function() {
      return val.toUpperCase();
    }
  }
}
class Book {
  @upperCase
  id = "az092b";
  getId() {
    return `${this.id}`;
  }
  //other implementation here
}
let obj = new Book("HP", "1245-533552");
console.log(obj.getId());
//AZ092B

//Before decorator
class MyApp extends React.Component {
  // ...define your main app here
}
export default connect(mapStateToProps, mapDispatchToProps)(MyApp);
//After decorator
@connect(mapStateToProps, mapDispatchToProps)
export default class MyApp extends React.Component {
  // ...define your main app here
}