Задание:

Напишите на C# библиотеку для поставки внешним клиентам, которая умеет вычислять площадь круга по радиусу и треугольника по трем сторонам. Дополнительно к работоспособности оценим:

• Юнит-тесты

• Легкость добавления других фигур

• Вычисление площади фигуры без знания типа фигуры в compile-time

• Проверку на то, является ли треугольник прямоугольным

Task:

Write a C# library for distribution to external clients, capable of calculating the area of a circle based on its radius and the area of a triangle based on its three edges. In addition to functionality, we will value:

• Unit tests

• Ease of adding other shapes

• Calculating the area of a shape without knowing the type of the shape at compile-time

• Checking whether a triangle is rectangular

Thanks to Mindbox for this cool task.

I wanted to make it as good as possible and overengineered it in the end.
Reference values for expected test results were compared to results at OmniCalculator.com.
Any new shape can be created with this code-base, e.g. Tetragon and Rectangle implementation took only ~3-4 minutes.
Project can be extended with 3D shapes.
Unit-tests coverage is close to 100%.
There's a shape calculation API used as an example of external usage.

Inhertitance and interfaces implementation establish abstraction layers.

IShape2D shape = Triangle.Regular(1);
shape.Area // 0.43301270189221902
if(shape is IEdges IEdges)
    polygon.Edges // [1, 1, 1]

It's recommended to use interfaces whenever possible.

Usage (See tests for more examples):

• Circle

var circle = Circle.WithRadius(4);
shape.Perimeter // 25.132741228718345
shape.Area // 50.26548245743669

shape = Circle.WithArea(cirlce.Area);
shape.Radius // 4

shape = Circle.WithPerimeter(cirlce.Perimeter);
shape.Radius // 4

• Triangle

var shape = Triangle.WithEdges(2, 3, 4);
shape.Perimeter // 9
shape.Area // 2.904737509655562
shape.Is(PolygonType.Scalene) // true

shape = Triangle.WithEdges(3, 4, 5);
shape.Is(TriangleType.Rectangular) // true

• Tetragon

var shape = Tetragon.WithVertices((0, 0), (1, 2), (2, 0), (1, -2)); // rhombus
shape.Area // 4
shape.Perimeter // 8.9442719099991592

• Rectangle

var shape = Rectangle.WithEdges(1); // 1x1 square
shape.Perimeter // 4
shape.Area // 1
shape.Is(PolygonType.Equilateral) // true

shape = Rectangle.WithEdges(1, 2); // 1x2 rectangle
shape.Area // 2

• Polygon

var shape = Polygon.Regular(5); // pentagon with each side equal to 1
shape.Area // 1.720477400588968
shape.Perimeter // 5