using System.Runtime.InteropServices;
using System.Security.Cryptography;

namespace XFESystem.DriverOracle;

internal sealed class VectorCase
{
    public const int Count = 65_537, GuardWords = 32, BlockThreads = 256;
    public const long MaximumDeviceBytes = 4 * 1024 * 1024;
    public uint Seed { get; }
    public uint Poison { get; }
    public uint[] A { get; } = new uint[Count];
    public uint[] B { get; } = new uint[Count];
    public uint[] Initial { get; } = new uint[Count + 2 * GuardWords];
    public uint[] Expected { get; } = new uint[Count + 2 * GuardWords];
    public long DeviceBytes => ((long)A.Length + B.Length + Initial.Length) * sizeof(uint);

    public VectorCase(uint seed)
    {
        Seed = seed; Poison = 0xDEADBEEFu ^ seed;
        for (int index = 0; index < Count; index++)
        {
            A[index] = unchecked((0xFFFFFF00u + (uint)index * 0x9E3779B9u) ^ seed);
            B[index] = unchecked(0x10203040u + ((uint)index ^ seed) * 0x85EBCA6Bu);
            Initial[GuardWords + index] = Poison;
            Expected[GuardWords + index] = unchecked(A[index] + B[index]);
        }
        for (int index = 0; index < GuardWords; index++)
        {
            Initial[index] = Expected[index] = 0xCAFE0000u ^ seed ^ (uint)index;
            Initial[GuardWords + Count + index] = Expected[GuardWords + Count + index] = unchecked(0xBADC0000u ^ (seed + (uint)index));
        }
        if (DeviceBytes >= MaximumDeviceBytes) throw new InvalidOperationException("The fixed test exceeds the device allocation bound.");
    }

    public object Verify(uint[] actual)
    {
        if (actual.Length != Expected.Length) throw new InvalidOperationException("Result length differs from the complete guarded allocation.");
        for (int index = 0; index < actual.Length; index++)
            if (actual[index] != Expected[index]) throw new InvalidOperationException($"GPU result/guard mismatch at allocation word {index}: expected {Expected[index]:x8}, received {actual[index]:x8}.");
        int changed = Enumerable.Range(0, Count).Count(index => actual[GuardWords + index] != Poison);
        if (changed == 0) throw new InvalidOperationException("The output remains poisoned.");
        return new { AllElementsMatched = true, MatchedElements = Count, PrefixGuardWords = GuardWords,
            SuffixGuardWords = GuardWords, PrefixGuardPassed = true, SuffixGuardPassed = true,
            ChangedFromPoison = changed, Modulo32OverflowElements = Enumerable.Range(0, Count).Count(index => (ulong)A[index] + B[index] > uint.MaxValue),
            ExpectedSha256 = Hash(Expected), ActualSha256 = Hash(actual), OutputBodySha256 = Hash(actual.AsSpan(GuardWords, Count)),
            InputASha256 = Hash(A), InputBSha256 = Hash(B) };
    }

    public static string Hash(ReadOnlySpan<uint> data) => Convert.ToHexStringLower(SHA256.HashData(MemoryMarshal.AsBytes(data)));
    public static int SelfTest()
    {
        int checks = 0;
        foreach (uint seed in new[] { 0u, 1u, uint.MaxValue, 0x12345678u })
        {
            var vector = new VectorCase(seed); _ = vector.Verify((uint[])vector.Expected.Clone()); checks++;
            foreach (int index in new[] { 0, GuardWords - 1, GuardWords, GuardWords + Count - 1, GuardWords + Count, vector.Expected.Length - 1 })
            {
                var bad = (uint[])vector.Expected.Clone(); bad[index] ^= 1;
                bool rejected = false;
                try { vector.Verify(bad); } catch (InvalidOperationException) { rejected = true; }
                if (!rejected) throw new InvalidOperationException("The verifier accepted a corrupted result or guard.");
                checks++;
            }
            bool poisonRejected = false;
            try { vector.Verify(vector.Initial); } catch (InvalidOperationException) { poisonRejected = true; }
            if (!poisonRejected) throw new InvalidOperationException("The verifier accepted untouched poison.");
            checks++;
        }
        if (Count % BlockThreads == 0) throw new InvalidOperationException("The launch must exercise the partial-block bound.");
        return checks + 1;
    }
}