// Exercise 1: own and dispose resources correctly (easy)
//
// FakeConnection simulates an unmanaged resource: it increments OpenCount when created and
// decrements it when disposed. Disposing twice must not decrement twice.
//
// Implement:
//   - FakeConnection.Dispose(): idempotent (only the first call decrements OpenCount).
//   - Repository: OWNS a FakeConnection it creates in its constructor, so it must implement IDisposable
//     and dispose the connection in Dispose().
//   - CountRows(n): opens `n` repositories one at a time with `using` so that none remain open afterwards,
//     returning the sum of repo.Rows().
//
// Run with: dotnet run (inside a console project).

using System;

class FakeConnection : IDisposable
{
    public static int OpenCount;
    public FakeConnection() { OpenCount++; }
    public void Dispose()
    {
        // TODO: decrement OpenCount only once
    }
}

class Repository : IDisposable
{
    readonly FakeConnection _conn = new FakeConnection();
    public int Rows() => 10;
    public void Dispose()
    {
        // TODO: dispose the connection we own
    }
}

class Program
{
    static int CountRows(int n)
    {
        int total = 0;
        for (int i = 0; i < n; i++)
        {
            var repo = new Repository(); // TODO: make sure it's disposed
            total += repo.Rows();
        }
        return total;
    }

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

        var c = new FakeConnection();
        c.Dispose(); c.Dispose();
        Check("Dispose is idempotent", FakeConnection.OpenCount == 0);

        Check("CountRows sums rows", CountRows(5) == 50);
        Check("no connections left open", FakeConnection.OpenCount == 0);

        try { using var r = new Repository(); throw new InvalidOperationException(); }
        catch (InvalidOperationException) { }
        Check("disposed even when an exception is thrown", FakeConnection.OpenCount == 0);

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