XFESystem

namespace XFESystem.Kernel;

/// <summary>
/// Bounds adapter discovery with the monotonic clock, independently of the PIT
/// and its software timer registry. The caller supplies the already-running
/// LAPIC interrupt wait; neither delegate may block indefinitely.
/// </summary>
internal static class NativeNetworkBootWait
{
    internal const int TimeoutSeconds = 5;

    internal static bool WaitUntilReady(Func<bool> pollReady, Func<long> monotonicTimestamp,
        long timestampFrequency, Action waitOneInterrupt)
    {
        ArgumentNullException.ThrowIfNull(pollReady);
        ArgumentNullException.ThrowIfNull(monotonicTimestamp);
        ArgumentNullException.ThrowIfNull(waitOneInterrupt);
        // Keep the budget below half the counter range. This permits an
        // unsigned elapsed subtraction across signed Stopwatch wrap without
        // overflowing an absolute deadline or accepting a backwards clock.
        if (timestampFrequency <= 0 || timestampFrequency > long.MaxValue / TimeoutSeconds)
            throw new ArgumentOutOfRangeException(nameof(timestampFrequency));

        ulong budget = (ulong)timestampFrequency * TimeoutSeconds;
        long started = monotonicTimestamp();
        while (true)
        {
            if (Elapsed(monotonicTimestamp(), started) >= budget) return false;
            bool ready = pollReady();
            // Count time spent polling as part of the same total budget. A
            // readiness result obtained at or after the deadline is too late.
            if (Elapsed(monotonicTimestamp(), started) >= budget) return false;
            if (ready) return true;
            waitOneInterrupt();
        }
    }

    private static ulong Elapsed(long current, long started) => unchecked((ulong)(current - started));
}