using System;
using System.Reflection;

namespace Glass.Testbed
{
    /// <summary>
    /// Reads how many bytes the calling thread has allocated, for the frame readout.
    /// </summary>
    /// <remarks>
    /// This project targets netstandard2.0, which predates GC.GetAllocatedBytesForCurrentThread, so it's bound by
    /// reflection once at startup instead (see UnitTestSharp.AllocationCounter for the same trick).
    /// </remarks>
    public static class AllocationCounter
    {
        private static readonly Func<long> source = BindToRuntime();

        private static Func<long> BindToRuntime()
        {
            MethodInfo counter = typeof(GC).GetMethod("GetAllocatedBytesForCurrentThread",
                BindingFlags.Public | BindingFlags.Static, null, Type.EmptyTypes, null);

            return counter == null ? null : (Func<long>)counter.CreateDelegate(typeof(Func<long>));
        }

        /// <summary>
        /// Bytes the calling thread has allocated since it started, or zero on a runtime that won't say.
        /// </summary>
        public static long BytesAllocatedOnThisThread()
        {
            return source?.Invoke() ?? 0;
        }
    }
}