using System;
using System.Diagnostics;

namespace TestsForUnitTestSharp
{
    /// <summary>
    /// Spins the calling thread until it has used a given amount of CPU, however contended the machine is.
    /// </summary>
    public static class CpuBurner
    {
        /// <summary>
        /// Bounds a burn that can't reach its target, so a broken clock fails its test instead of hanging it.
        /// </summary>
        public static readonly TimeSpan WallClockCap = TimeSpan.FromSeconds(5);

        public static void Burn(TimeSpan cpu)
        {
            // Measured on the process rather than the thread, so the burn doesn't lean on the ThreadCpuClock that
            // several callers are testing.  Tests run one at a time, so this thread is nearly all the process uses.
            Process process = Process.GetCurrentProcess();
            TimeSpan target = process.TotalProcessorTime + cpu;
            var elapsed = Stopwatch.StartNew();
            double accumulator = 0;
            while (elapsed.Elapsed < WallClockCap)
            {
                for (int i = 0; i < 10000; ++i)
                {
                    accumulator += Math.Sqrt(accumulator + 1);
                }

                if (process.TotalProcessorTime >= target)
                {
                    return;
                }
            }
        }
    }
}