// Exercise 1: sequential vs concurrent awaiting (easy)
//
// FetchPriceAsync simulates an I/O call that takes ~200ms.
//
// Implement:
//   - SumSequentialAsync(ids): awaits each FetchPriceAsync one after another
//     and returns the sum. (Expected total time: ~200ms * ids.Length.)
//   - SumConcurrentAsync(ids): STARTS every FetchPriceAsync first, then
//     awaits them all with Task.WhenAll and returns the sum.
//     (Expected total time: ~200ms regardless of ids.Length.)
//
// The self-check measures elapsed time with a Stopwatch, so a "concurrent"
// version that secretly awaits in a loop will FAIL.
//
// Run with: dotnet run (inside a console project).

using System;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;

class Program
{
    static async Task<int> FetchPriceAsync(int id)
    {
        await Task.Delay(200); // stands in for a network call
        return id * 10;
    }

#pragma warning disable IDE0060, CS1998
    static async Task<int> SumSequentialAsync(int[] ids)
    {
        // TODO: foreach id, total += await FetchPriceAsync(id)
        return 0;
    }

    static async Task<int> SumConcurrentAsync(int[] ids)
    {
        // TODO: var tasks = ids.Select(FetchPriceAsync).ToArray();
        //       int[] prices = await Task.WhenAll(tasks);
        return 0;
    }
#pragma warning restore IDE0060, CS1998

    static async Task Main()
    {
        int pass = 0, total = 0;
        int[] ids = { 1, 2, 3, 4, 5 };

        var sw = Stopwatch.StartNew();
        int seq = await SumSequentialAsync(ids);
        long seqMs = sw.ElapsedMilliseconds;

        sw.Restart();
        int con = await SumConcurrentAsync(ids);
        long conMs = sw.ElapsedMilliseconds;

        total++;
        if (seq == 150 && seqMs >= 900) { Console.WriteLine($"PASS: sequential sum ({seqMs}ms)"); pass++; }
        else Console.WriteLine($"FAIL: sequential sum={seq} in {seqMs}ms (expected 150, >=900ms)");

        total++;
        if (con == 150 && conMs < 600) { Console.WriteLine($"PASS: concurrent sum ({conMs}ms)"); pass++; }
        else Console.WriteLine($"FAIL: concurrent sum={con} in {conMs}ms (expected 150, <600ms)");

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