using System.Diagnostics;
using Npgsql;

var csb = new NpgsqlConnectionStringBuilder("Host=localhost;Database=npgsql_tests;Username=postgres;Password=postgres;")
{
    MaxPoolSize = 1,
    Timeout = 5
};
var dataSource = NpgsqlDataSource.Create(csb);

var sw = Stopwatch.StartNew();

await using var connection1 = await OpenConnectionAsync(1);

// Connection pool is exhausted, so opening a second connection will block
var pending = OpenConnectionAsync(2);

Console.WriteLine($"[{sw.ElapsedMilliseconds}] Disposing data source...");
await dataSource.DisposeAsync().ConfigureAwait(false);
Console.WriteLine($"[{sw.ElapsedMilliseconds}] Disposed data source.");

// Connection 2 is still trying to connect until it eventually times out
try { await using var connection2 = await pending; } catch { /* ignored */ }

return;

async Task<NpgsqlConnection> OpenConnectionAsync(int connectionNumber)
{
    try
    {
        Console.WriteLine($"[{sw.ElapsedMilliseconds}] Opening connection {connectionNumber}...");
        var connection = await dataSource.OpenConnectionAsync().ConfigureAwait(false);
        Console.WriteLine($"[{sw.ElapsedMilliseconds}] Connection {connectionNumber} opened");
        return connection;
    }
    catch (Exception ex)
    {
        Console.Error.WriteLine($"[{sw.ElapsedMilliseconds}] Failed to open connection {connectionNumber}: {ex.Message}");
        throw;
    }
}