void main(){
    print('Hello world');
}

int year = 2021; // explicitly typed int
var month = 01; // inferred int created with var
double day; // null

p = 'aaa'; // error when compiling

dynamic numberOfCats; // dynamic variable can have any type of value

numberOfCats = '3'; // dynamic String
numberOfCats = 0.2; // dynamic double
bool isCat = true; // boolean

const hourInDay = 24; // Compile-time constants
hourInDay = 23; // error can't assign to the const variable

final age = 23; // Immutables with final
age = 24; // error can't assign to the final variable

var animal = 'fish';
if (animal == 'cat' || animal = 'bear'){
    print('That is a cute animal');
} else if (animal == 'dinosaur'){
    print('Dinosaur is extincted');
} else{
   print('That is a fly animal');
}

for (int i=0 ;i < 69; i++) {
  print(i);
} // prints 0 to 69

final list = [ 'a', 'b', 'c' , 'd', 'e'];

for(final i in list){
   print(i)
} // prints: a, b, c, d, e

final list = [ 1, 2, 3, 4, 5, 6];
list.forEach(print)

int x = 9;
int y = 6;

print('${x + y}'); // 15
print('${"flutter".toUpperCase()}'); // 'FLUTTER'
print('$x$y'); // 96

// Named Function
  String fullName() {
    String firstName = "Barry";
    String lastName = "Allen";
    return '$firstName $lastName'; // 'Barry Allen'
  }

  int lengthOfText(String text) {
    return text.length; // returns length of text
  }

  int length = lengthOfText('200lab'); // 6

  // Arrow Syntak Function
  int sum(int a, int b) => a + b;

  // Optional named arguments
  int sumNumber(int a, int b, {int c = 0}) {
    return a + b + c;
  }
  print(sumNumber(1, 2, c: 3)); // 6

  // Lamda Function
  var list = [1, 4, 3, 2, 5];
  var odds = list.where((n) => n % 2 == 1).toList();
  print(odds); // [1, 3, 5]

  // High Order Function
  list.sort((a,b){
    return a > b ? 1 : -1;
  });
  print(list); // prints: [1, 2, 3, 4, 5]

var s1 = "456";
var s2 = "12.21";
var s3 = "18.01";
var s4 = "12.a56";

print(int.parse(s1)); // 456
print(double.parse(s2)); // 12.21
print(num.parse(s3)); // 12.21
print(num.parse(s4)); // error FormatException, null

int y; // initial null value
y ??= 10; // if y null, y will be 10

print(y ?? 08); // result: 08. Display the value on the left if it's not null else return the value on the right

// dynamic list
  var countryList = ['Vietnam', 'German', 'Poland'];
  print(countryList.length); // 3
  print(countryList[1]); // German
  countryList[2] = countryList[2].toUpperCase();
  print(countryList[2]); // POLAND

  countryList.insert(countryList.length, 'Thailand');
  print(countryList); // [Vietnam, German, POLAND, Thailand]
  print('${countryList.isEmpty}'); // false
  print('${countryList.last}'); // Thailand

  var fixedList = List<int>(2); // fixed list size

var anotherSet = {1, 3, 5, 7};

  print('${anotherSet.contains(69)}'); // false

  anotherSet.add(9);
  print(anotherSet); // {1, 3, 5, 7, 9}

  anotherSet.remove(1);
  print(anotherSet); // {3, 5, 7, 9}

  anotherSet.addAll([11, 13]);
  print(anotherSet); // {3, 5, 7, 9, 11, 13}

  var declareSet = <int>{15, 17};
  anotherSet = anotherSet.union(declareSet);
  print(anotherSet); // {3, 5, 7, 9, 11, 13, 15, 17}

// initial Map
  final student = {
    "id": 1,
    "name": "Barry Allen",
    "age": 23,
  };

  print(student); // {id: 1, name: Barry Allen, age: 23}

  // element access by key
  print(student['name']); // print: Barry Allen

  // access all keys
  student.keys.forEach(print); // prints: id, name, age

  // update value by key
  student.update("age", (value) => 18);

  print(student); // {id: 1, name: Barry Allen, age: 18}

  // Loop over key-value
  student.forEach((key, value) {
    print('$key - $value');
  }); /*
        id - 1
        name - Barry Allen
        age - 18
      */

class Cat {
    // field
    String name = 'Milo';

    // function
    void call(){
        print('Meow meow');
    }
}

class Location {
  // Properties
  double _lat;
  double _lng;

  // get value
  double get long => _lng;
  double get lat => _lat;

  // set value
  set latitude (double value) => _lat = value;
  set longitude (double value) => _lng = value;

  // constructor
  Location(this._lat,this._lng);

  // named constructor
  Location.withPosition(double lat,double lang){
    _lat = lat;
    _lng = lang;
  }
}

void main(){

  final location = Location(69.96,96.69);
  final location2 = Location.withPosition(12.23,23.21);

  location2.latitude = 11.0;
  location2.longitude = 12.21;

  print('new latitude: ${location2.lat}'); // 11.0
  print('new longitude: ${location2.long}'); // 12.21

}

class Channel{
    
    static String name = 'Channel name' ;

    static void changeChannelName(String name){
        print('New name: $name');
    }
}

enum WeekDays { MON, TUES, WED, THURS, FRI, SAT,SUN, }

void main(){
  print(WeekDays.values); // [WeekDays.SUN, WeekDays.MON, WeekDays.TUES, WeekDays.WED, WeekDays.THURS, WeekDays.FRI, WeekDays.SAT]

  var today = WeekDays.SUN;

  switch(today){
    case WeekDays.MON:
    case WeekDays.TUES:
    case WeekDays.WED:
    case WeekDays.THURS:
    case WeekDays.FRI:
      print('Working day');
      break;
    case WeekDays.SAT:
    case WeekDays.SUN:
      print('Relaxing day');
      break;
  }
}

class Person {
  String name;
  int age;

  Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
}

class Student extends Person{
    String id;
    Student({String id, String name, int age}) : super(name, age){
      this.id = id;
    }
}

void main() {
  final student1 = Student(id: "123",name: "Barry",age: 22);
  
  print('id: ${student1.id}');
  print('name: ${student1.name}');
  print('age: ${student1.age}');
  
}

class Person {
  String name;
  int age;
  int money = 0;

  Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
}

abstract class LenderBehavior {
  bool lendMoney(BorrowerBehavior borrower, int money);
  requestPayment();
}

abstract class BorrowerBehavior {
  void askForMoney(LenderBehavior lender, int money);
  void receiveMoney(LenderBehavior lender, money);
  int payMoneyBack();
}

class Lender extends Person implements LenderBehavior {
  BorrowerBehavior borrower;
  Lender(String name, int age) : super(name, age);

  @override
  bool lendMoney(BorrowerBehavior borrower, int money) {
    // if lender doesn't have enough money => false;
    if (this.money < money) return false;

    this.borrower = borrower;
    this.money -= money;

    // give money for borrower
    borrower.receiveMoney(this, money);

    return true;
  }

  @override
  requestPayment() {
    int returnMoney = borrower.payMoneyBack();

    if (returnMoney == null) {
      print("Borrower doesn't have enough money");
    } else {
      print("Yeah he is awesome guy");
      this.money += returnMoney;
      this.borrower = null;
    }
  }
}

class Borrower extends Person implements BorrowerBehavior {
  LenderBehavior lender;
  int debt = 0;

  Borrower(String name, int age) : super(name, age);

  @override
  void askForMoney(LenderBehavior lender, int money) {
    if (lender.lendMoney(this, money)) {
      print("what a hero");
    } else {
      print("I have to find someone else");
    }
  }

  @override
  int payMoneyBack() {
    int returnMoney;
    // if borrower has enough money for pay back to lender
    if (money >= debt) {
      money -= debt;
      returnMoney = debt;
      debt = 0;
      this.lender = null;
    } else {
      return null;
    }
    return returnMoney;
  }

  @override
  void receiveMoney(LenderBehavior lender, money) {
    this.lender = lender;
    debt = money;
    this.money += money;
  }
}

void main() {
  Lender lenderObj = new Lender("Barry", 22);
  lenderObj.money = 2000;
  Borrower borrowerObj = new Borrower("Duong", 18);

  // Example 1
  borrowerObj.askForMoney(lenderObj, 1000); // what a hero
  lenderObj.requestPayment(); // Yeah he is awesome guy

  // Example 2
  borrowerObj.askForMoney(lenderObj, 1000);
  borrowerObj.money = 800;
  lenderObj.requestPayment(); // Borrower doesn't have enough money
}