#4 create a factory of codelabs --> Intro to Dart for Java devs!

shape.dart

import 'dart:math';

// 2 Create a factory constructor
abstract class Shape {
  factory Shape(String type) {
    if (type == 'circle') return Circle(2);
    if (type == 'square') return Square(2);
    throw 'Can\'t create $type.';
  }
  num get area;
}

class Circle implements Shape {
  final num radius;
  Circle(this.radius);
  num get area => pi * pow(radius, 2);
}

class CircleMock implements Circle {
  num area;
  num radius;
}

class Square implements Shape {
  final num side;
  Square(this.side);
  num get area => pow(side, 2);
}

// 1 Create a top-level function
// Shape shapeFactory(String type) {
//   if (type == 'circle') return Circle(2);
//   if (type == 'square') return Square(2);
//   throw 'Can\'t create $type.';
// }

main() {
//   final circle = shapeFactory('circle');
//   final square = shapeFactory('square');
  final circle = Shape('circle');
  final square = Shape('square');
  print(circle.area);
  print(square.area);
}

shape2.dart

import 'dart:math';

abstract class Shape {
  factory Shape(String type) {
    if (type == 'circle') return Circle(2);
    if (type == 'square') return Square(2);
    // To trigger exception, don't implement a check for 'triangle'.
    throw 'Can\'t create $type.';
  }
  num get area;
}

class Circle implements Shape {
  final num radius;
  Circle(this.radius);
  num get area => pi * pow(radius, 2);
}

class Square implements Shape {
  final num side;
  Square(this.side);
  num get area => pow(side, 2);
}

class Triangle implements Shape {
  final num side;
  Triangle(this.side);
  num get area => pow(side, 2) / 2;
}

main() {
  try {
    print(Shape('circle').area);
    print(Shape('square').area);
    print(Shape('triangle').area);
  } catch (err) {
    print(err);
  }
}