// Exercise 1: Func/Action composition (easy)
//
// Implement:
//   - Compose(f, g): returns a Func<int,int> that computes g(f(x))
//   - ApplyN(f, n): returns a Func<int,int> that applies f n times
//     (n = 0 returns the identity function)
//   - MakeCounter(): returns an (Action increment, Func<int> read) pair that
//     share one captured counter variable — the closure is the only state.
//   - Where(items, predicate): your own filter using Predicate<T>, no LINQ.
//
// Run with: dotnet run (inside a console project).

using System;
using System.Collections.Generic;

class Program
{
#pragma warning disable IDE0060
    static Func<int, int> Compose(Func<int, int> f, Func<int, int> g)
    {
        // TODO
        return x => 0;
    }

    static Func<int, int> ApplyN(Func<int, int> f, int n)
    {
        // TODO
        return x => 0;
    }

    static (Action increment, Func<int> read) MakeCounter()
    {
        // TODO
        return (() => { }, () => 0);
    }

    static List<T> Where<T>(IEnumerable<T> items, Predicate<T> predicate)
    {
        // TODO
        return new List<T>();
    }
#pragma warning restore IDE0060

    static void Main()
    {
        int pass = 0, total = 0;

        total++;
        var addThenDouble = Compose(x => x + 1, x => x * 2);
        if (addThenDouble(3) == 8) { Console.WriteLine("PASS: Compose"); pass++; }
        else Console.WriteLine("FAIL: Compose(3) = " + addThenDouble(3));

        total++;
        var plus3 = ApplyN(x => x + 1, 3);
        var identity = ApplyN(x => x * 100, 0);
        if (plus3(10) == 13 && identity(7) == 7) { Console.WriteLine("PASS: ApplyN"); pass++; }
        else Console.WriteLine("FAIL: ApplyN");

        total++;
        var (inc, read) = MakeCounter();
        var (inc2, read2) = MakeCounter();
        inc(); inc(); inc2();
        if (read() == 2 && read2() == 1) { Console.WriteLine("PASS: independent closures"); pass++; }
        else Console.WriteLine($"FAIL: counters {read()} / {read2()}");

        total++;
        var evens = Where(new[] { 1, 2, 3, 4, 5, 6 }, n => n % 2 == 0);
        if (string.Join(",", evens) == "2,4,6") { Console.WriteLine("PASS: Where"); pass++; }
        else Console.WriteLine("FAIL: Where, got " + string.Join(",", evens));

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