// Exercise 1: pattern matching with records (easy)
//
// Implement with switch EXPRESSIONS (no if/else chains):
//   Describe(Shape s):
//     Circle with Radius 0 → "point"; Circle → "circle r=<R>";
//     Rect with Width == Height → "square <W>"; Rect → "rect <W>x<H>"; null → "nothing".
//   Grade(int score): >= 90 "A"; 80..89 "B"; < 0 or > 100 "invalid"; otherwise "C". (Check invalid first.)
//   Format numbers with the invariant culture (FormattableString.Invariant) so "2.5" doesn't become "2,5".
//   Summarize(int[] xs) with list patterns: [] "empty"; [x] "one: x"; [a, b] "two: a,b"; [first, .., last] "first..last".
//
// Run with: dotnet run (inside a console project).

using System;

abstract record Shape;
record Circle(double Radius) : Shape;
record Rect(double Width, double Height) : Shape;

class Program
{
    static string Describe(Shape s) => "";   // TODO
    static string Grade(int score) => "";    // TODO
    static string Summarize(int[] xs) => "";  // TODO

    static void Main()
    {
        int pass = 0, total = 0;
        void Check(string name, bool ok) { total++; if (ok) pass++; Console.WriteLine($"{(ok ? "PASS" : "FAIL")}: {name}"); }

        Check("point", Describe(new Circle(0)) == "point");
        Check("circle", Describe(new Circle(2.5)) == "circle r=2.5");
        Check("square", Describe(new Rect(3, 3)) == "square 3");
        Check("rect", Describe(new Rect(2, 5)) == "rect 2x5");
        Check("null", Describe(null) == "nothing");
        Check("grades", Grade(95) == "A" && Grade(80) == "B" && Grade(79) == "C" && Grade(101) == "invalid" && Grade(-1) == "invalid");
        Check("lists", Summarize(new int[0]) == "empty" && Summarize(new[] { 7 }) == "one: 7" && Summarize(new[] { 1, 2 }) == "two: 1,2" && Summarize(new[] { 1, 2, 3, 9 }) == "1..9");
        var c = new Circle(1);
        Check("records: value equality and with", c == new Circle(1) && (c with { Radius = 2 }) == new Circle(2) && c.Radius == 1);

        Console.WriteLine($"--- {pass}/{total} checks passed ---");
    }
}