using System;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        await WithContinuation();

        Console.WriteLine();

        await TryCatchWhenAll();

    }

    public static async Task WithContinuation() {

        Console.WriteLine($"Begin {nameof(WithContinuation)}");

        List<Task<bool?>> tasks = BuildTasks();     

        Console.WriteLine($"\ttasks has {tasks.Count} total entries, 2 with exceptions");

        IEnumerable<bool?> results = await Task.WhenAll(tasks)

                .ContinueWith((Task<bool?[]> t) => tasks.Where(st => st.Exception == null).Select(st => st.Result));

        bool?[] completedResults = results.Select(r => {

            Console.WriteLine($"\t\t\tresult: {r}");

            return r;

        }).ToArray();

        Console.WriteLine($"\tcompletedResults has {completedResults.Length} total entries");

        Console.WriteLine($"End {nameof(WithContinuation)}");

    }

    public static async Task TryCatchWhenAll() {

        Console.WriteLine($"Begin {nameof(TryCatchWhenAll)}");

        List<Task<bool?>> tasks = BuildTasks();

        Console.WriteLine($"\ttasks has {tasks.Count} total entries, 2 with exceptions");

        IEnumerable<bool?> results = null;

        var allTasksTask = Task.WhenAll(tasks);

        try {

            IEnumerable<bool?> taskResults = await allTasksTask;

        }

        catch (AggregateException ex) {

            Console.WriteLine($"\tcaught aggregate exception: {ex.InnerExceptions.Count}");

        }

        catch (Exception ex) {

            Console.WriteLine($"\tcaught exception: {ex.Message}");

            if (allTasksTask.Exception != null) {

                Console.WriteLine($"\twhenall exception: {allTasksTask.Exception.GetType()}");

            }

        }

        bool?[] completedResults = tasks.Where(t => t.Exception == null && t.IsCompletedSuccessfully).Select(t => {

            Console.WriteLine($"\t\t\tresult: {t.Result}");

            return t.Result;

        }).ToArray();

        Console.WriteLine($"\tcompletedResults has {completedResults.Length} total entries");

        Console.WriteLine($"End {nameof(TryCatchWhenAll)}");

    }

    public static List<Task<bool?>> BuildTasks() {

        List<Task<bool?>> tasks = new ();       

        tasks.Add(Task.FromResult((bool?)true));

        tasks.Add(Task.FromException<bool?>(new ArgumentNullException("message")));     

        tasks.Add(Task.FromResult((bool?)true));

        tasks.Add(Task.FromResult((bool?)false));

        tasks.Add(Task.FromException<bool?>(new Exception("second Exception")));

        tasks.Add(GetActualTask());

        return tasks;

    }

    async public static Task<bool?> GetActualTask() {

        await Task.Delay(500);

        Console.WriteLine("\t\tDelayed task finished");

        return (bool?)true;

    }

}