java-topology/defects/btcpayserver-0002/test/btcpayserver-0002-test.cs

// Unit test for btcpayserver-0002: AppService gap-fill O(D*S) series.All inside foreach
// Demonstrates quadratic vs linear behavior when filling date gaps in sales stats.
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace BTCPayServer.Tests.CWE407
{
    public class SalesItem
    {
        public DateTime Date { get; set; }
        public string Label { get; set; }
        public int SalesCount { get; set; }
    }

    public static class BtcPayServer0002Test
    {
        // --- ORIGINAL (defective): O(D * S) ---
        static void FillGapsOriginal(List<SalesItem> series, int numberOfDays)
        {
            foreach (var i in Enumerable.Range(0, numberOfDays))
            {
                var date = (DateTimeOffset.UtcNow - TimeSpan.FromDays(i)).Date;
                if (series.All(e => e.Date != date))
                {
                    series.Add(new SalesItem { Date = date, Label = date.ToString("MMM dd") });
                }
            }
        }

        // --- PATCHED: O(D + S) ---
        static void FillGapsPatched(List<SalesItem> series, int numberOfDays)
        {
            var existingDates = new HashSet<DateTime>(series.Select(e => e.Date));
            foreach (var i in Enumerable.Range(0, numberOfDays))
            {
                var date = (DateTimeOffset.UtcNow - TimeSpan.FromDays(i)).Date;
                if (!existingDates.Contains(date))
                {
                    series.Add(new SalesItem { Date = date, Label = date.ToString("MMM dd") });
                    existingDates.Add(date);
                }
            }
        }

        static List<SalesItem> MakeSparse(int days, int gapEvery)
        {
            var list = new List<SalesItem>();
            for (int i = 0; i < days; i++)
            {
                if (i % gapEvery != 0) continue;
                var date = (DateTimeOffset.UtcNow - TimeSpan.FromDays(i)).Date;
                list.Add(new SalesItem { Date = date, Label = date.ToString("MMM dd"), SalesCount = 1 });
            }
            return list;
        }

        public static void Main(string[] args)
        {
            int D = 3000; // exaggerated for benchmark
            int gapEvery = 5;

            // Warmup
            var warmup1 = MakeSparse(D, gapEvery);
            FillGapsOriginal(warmup1, D);
            var warmup2 = MakeSparse(D, gapEvery);
            FillGapsPatched(warmup2, D);

            var sw = Stopwatch.StartNew();
            for (int run = 0; run < 3; run++)
            {
                var s = MakeSparse(D, gapEvery);
                FillGapsOriginal(s, D);
            }
            sw.Stop();
            long originalMs = sw.ElapsedMilliseconds;

            sw.Restart();
            for (int run = 0; run < 3; run++)
            {
                var s = MakeSparse(D, gapEvery);
                FillGapsPatched(s, D);
            }
            sw.Stop();
            long patchedMs = sw.ElapsedMilliseconds;

            double ratio = (double)originalMs / Math.Max(1, patchedMs);

            Console.WriteLine($"D = {D}, gap every {gapEvery} days");
            Console.WriteLine($"Original (List.All):  {originalMs} ms");
            Console.WriteLine($"Patched  (HashSet):   {patchedMs} ms");
            Console.WriteLine($"Speedup ratio:        {ratio:F1}x");

            // Correctness
            var orig = MakeSparse(D, gapEvery);
            FillGapsOriginal(orig, D);
            var patched = MakeSparse(D, gapEvery);
            FillGapsPatched(patched, D);

            bool correct = orig.Count == patched.Count && orig.Count == D;
            Console.WriteLine($"Count match:          {(correct ? "PASS" : "FAIL")} (orig={orig.Count}, patched={patched.Count})");

            // Verify no duplicate dates
            bool noDupsOrig = orig.Select(e => e.Date).Distinct().Count() == orig.Count;
            bool noDupsPatched = patched.Select(e => e.Date).Distinct().Count() == patched.Count;
            Console.WriteLine($"No dups (original):   {(noDupsOrig ? "PASS" : "FAIL")}");
            Console.WriteLine($"No dups (patched):    {(noDupsPatched ? "PASS" : "FAIL")}");

            if (!correct || !noDupsOrig || !noDupsPatched)
                Environment.Exit(1);
        }
    }
}