using ILGPU;
using ILGPU.Algorithms;
using ILGPU.Runtime;
using OpenNest.Engine.BestFit;
using System;

namespace OpenNest.Gpu
{
    public class GpuSlideComputer : ISlideComputer
    {
        private readonly Context _context;
        private readonly Accelerator _accelerator;
        private readonly object _lock = new object();

        // ── Kernels ──────────────────────────────────────────────────

        private readonly Action<Index1D,
            ArrayView1D<double, Stride1D.Dense>,   // stationaryPrep
            ArrayView1D<double, Stride1D.Dense>,   // movingPrep
            ArrayView1D<double, Stride1D.Dense>,   // offsets
            ArrayView1D<double, Stride1D.Dense>,   // results
            int, int, int> _kernel;

        private readonly Action<Index1D,
            ArrayView1D<double, Stride1D.Dense>,   // stationaryPrep
            ArrayView1D<double, Stride1D.Dense>,   // movingPrep
            ArrayView1D<double, Stride1D.Dense>,   // offsets
            ArrayView1D<double, Stride1D.Dense>,   // results
            ArrayView1D<int, Stride1D.Dense>,      // directions
            int, int> _kernelMultiDir;

        private readonly Action<Index1D,
            ArrayView1D<double, Stride1D.Dense>,   // raw
            ArrayView1D<double, Stride1D.Dense>,   // prepared
            int> _prepareKernel;

        // ── Buffers ──────────────────────────────────────────────────

        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuStationaryRaw;
        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuStationaryPrep;
        private double[]? _lastStationaryData; // Keep CPU copy/ref for content check

        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuMovingRaw;
        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuMovingPrep;
        private double[]? _lastMovingData; // Keep CPU copy/ref for content check

        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuOffsets;
        private MemoryBuffer1D<double, Stride1D.Dense>? _gpuResults;
        private MemoryBuffer1D<int, Stride1D.Dense>? _gpuDirs;
        private int _offsetCapacity;

        public GpuSlideComputer()
        {
            _context = Context.CreateDefault();
            _accelerator = _context.GetPreferredDevice(preferCPU: false)
                .CreateAccelerator(_context);

            _kernel = _accelerator.LoadAutoGroupedStreamKernel<
                Index1D,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                int, int, int>(SlideKernel);

            _kernelMultiDir = _accelerator.LoadAutoGroupedStreamKernel<
                Index1D,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<int, Stride1D.Dense>,
                int, int>(SlideKernelMultiDir);

            _prepareKernel = _accelerator.LoadAutoGroupedStreamKernel<
                Index1D,
                ArrayView1D<double, Stride1D.Dense>,
                ArrayView1D<double, Stride1D.Dense>,
                int>(PrepareKernel);
        }

        public double[] ComputeBatch(
            double[] stationarySegments, int stationaryCount,
            double[] movingTemplateSegments, int movingCount,
            double[] offsets, int offsetCount,
            PushDirection direction)
        {
            var results = new double[offsetCount];
            if (offsetCount == 0 || stationaryCount == 0 || movingCount == 0)
            {
                Array.Fill(results, double.MaxValue);
                return results;
            }

            lock (_lock)
            {
                EnsureStationary(stationarySegments, stationaryCount);
                EnsureMoving(movingTemplateSegments, movingCount);
                EnsureOffsetBuffers(offsetCount);

                _gpuOffsets!.View.SubView(0, offsetCount * 2).CopyFromCPU(offsets);

                _kernel(offsetCount,
                    _gpuStationaryPrep!.View, _gpuMovingPrep!.View,
                    _gpuOffsets.View, _gpuResults!.View,
                    stationaryCount, movingCount, (int)direction);

                _accelerator.Synchronize();
                _gpuResults.View.SubView(0, offsetCount).CopyToCPU(results);
            }

            return results;
        }

        public double[] ComputeBatchMultiDir(
            double[] stationarySegments, int stationaryCount,
            double[] movingTemplateSegments, int movingCount,
            double[] offsets, int offsetCount,
            int[] directions)
        {
            var results = new double[offsetCount];
            if (offsetCount == 0 || stationaryCount == 0 || movingCount == 0)
            {
                Array.Fill(results, double.MaxValue);
                return results;
            }

            lock (_lock)
            {
                EnsureStationary(stationarySegments, stationaryCount);
                EnsureMoving(movingTemplateSegments, movingCount);
                EnsureOffsetBuffers(offsetCount);

                _gpuOffsets!.View.SubView(0, offsetCount * 2).CopyFromCPU(offsets);
                _gpuDirs!.View.SubView(0, offsetCount).CopyFromCPU(directions);

                _kernelMultiDir(offsetCount,
                    _gpuStationaryPrep!.View, _gpuMovingPrep!.View,
                    _gpuOffsets.View, _gpuResults!.View, _gpuDirs.View,
                    stationaryCount, movingCount);

                _accelerator.Synchronize();
                _gpuResults.View.SubView(0, offsetCount).CopyToCPU(results);
            }

            return results;
        }

        public void InvalidateStationary() => _lastStationaryData = null;
        public void InvalidateMoving() => _lastMovingData = null;

        private void EnsureStationary(double[] data, int count)
        {
            // Fast check: if same object or content is identical, skip upload
            if (_gpuStationaryPrep != null &&
                _lastStationaryData != null &&
                _lastStationaryData.Length == data.Length)
            {
                // Reference equality or content equality
                if (_lastStationaryData == data ||
                    new ReadOnlySpan<double>(_lastStationaryData).SequenceEqual(new ReadOnlySpan<double>(data)))
                {
                    return;
                }
            }

            _gpuStationaryRaw?.Dispose();
            _gpuStationaryPrep?.Dispose();

            _gpuStationaryRaw = _accelerator.Allocate1D(data);
            _gpuStationaryPrep = _accelerator.Allocate1D<double>(count * 10);

            _prepareKernel(count, _gpuStationaryRaw.View, _gpuStationaryPrep.View, count);
            _accelerator.Synchronize();

            _lastStationaryData = data; // store reference for next comparison
        }

        private void EnsureMoving(double[] data, int count)
        {
            if (_gpuMovingPrep != null &&
               _lastMovingData != null &&
               _lastMovingData.Length == data.Length)
            {
                if (_lastMovingData == data ||
                    new ReadOnlySpan<double>(_lastMovingData).SequenceEqual(new ReadOnlySpan<double>(data)))
                {
                    return;
                }
            }

            _gpuMovingRaw?.Dispose();
            _gpuMovingPrep?.Dispose();

            _gpuMovingRaw = _accelerator.Allocate1D(data);
            _gpuMovingPrep = _accelerator.Allocate1D<double>(count * 10);

            _prepareKernel(count, _gpuMovingRaw.View, _gpuMovingPrep.View, count);
            _accelerator.Synchronize();

            _lastMovingData = data;
        }

        private void EnsureOffsetBuffers(int offsetCount)
        {
            if (_offsetCapacity >= offsetCount)
                return;

            var newCapacity = System.Math.Max(offsetCount, _offsetCapacity * 3 / 2);

            _gpuOffsets?.Dispose();
            _gpuResults?.Dispose();
            _gpuDirs?.Dispose();

            _gpuOffsets = _accelerator.Allocate1D<double>(newCapacity * 2);
            _gpuResults = _accelerator.Allocate1D<double>(newCapacity);
            _gpuDirs = _accelerator.Allocate1D<int>(newCapacity);

            _offsetCapacity = newCapacity;
        }

        // ── Preparation Kernel ───────────────────────────────────────

        private static void PrepareKernel(
            Index1D index,
            ArrayView1D<double, Stride1D.Dense> raw,
            ArrayView1D<double, Stride1D.Dense> prepared,
            int count)
        {
            if (index >= count) return;
            var x1 = raw[index * 4 + 0];
            var y1 = raw[index * 4 + 1];
            var x2 = raw[index * 4 + 2];
            var y2 = raw[index * 4 + 3];

            prepared[index * 10 + 0] = x1;
            prepared[index * 10 + 1] = y1;
            prepared[index * 10 + 2] = x2;
            prepared[index * 10 + 3] = y2;

            var dx = x2 - x1;
            var dy = y2 - y1;

            // invD is used for parameter 't'. We use a small epsilon for stability.
            prepared[index * 10 + 4] = (XMath.Abs(dx) < 1e-9) ? 0 : 1.0 / dx;
            prepared[index * 10 + 5] = (XMath.Abs(dy) < 1e-9) ? 0 : 1.0 / dy;

            prepared[index * 10 + 6] = XMath.Min(x1, x2);
            prepared[index * 10 + 7] = XMath.Max(x1, x2);
            prepared[index * 10 + 8] = XMath.Min(y1, y2);
            prepared[index * 10 + 9] = XMath.Max(y1, y2);
        }

        // ── Main Slide Kernels ───────────────────────────────────────

        private static void SlideKernel(
            Index1D index,
            ArrayView1D<double, Stride1D.Dense> stationaryPrep,
            ArrayView1D<double, Stride1D.Dense> movingPrep,
            ArrayView1D<double, Stride1D.Dense> offsets,
            ArrayView1D<double, Stride1D.Dense> results,
            int sCount, int mCount, int direction)
        {
            if (index >= results.Length) return;

            var dx = offsets[index * 2];
            var dy = offsets[index * 2 + 1];

            results[index] = ComputeSlideLean(
                stationaryPrep, movingPrep, dx, dy, sCount, mCount, direction);
        }

        private static void SlideKernelMultiDir(
            Index1D index,
            ArrayView1D<double, Stride1D.Dense> stationaryPrep,
            ArrayView1D<double, Stride1D.Dense> movingPrep,
            ArrayView1D<double, Stride1D.Dense> offsets,
            ArrayView1D<double, Stride1D.Dense> results,
            ArrayView1D<int, Stride1D.Dense> directions,
            int sCount, int mCount)
        {
            if (index >= results.Length) return;

            var dx = offsets[index * 2];
            var dy = offsets[index * 2 + 1];
            var dir = directions[index];

            results[index] = ComputeSlideLean(
                stationaryPrep, movingPrep, dx, dy, sCount, mCount, dir);
        }

        private static double ComputeSlideLean(
            ArrayView1D<double, Stride1D.Dense> sPrep,
            ArrayView1D<double, Stride1D.Dense> mPrep,
            double dx, double dy, int sCount, int mCount, int direction)
        {
            const double eps = 0.00001;
            var minDist = double.MaxValue;
            var horizontal = direction >= 2;
            var oppDir = direction ^ 1;

            // ── Forward Pass: moving vertices vs stationary edges ─────
            for (int i = 0; i < mCount; i++)
            {
                var m1x = mPrep[i * 10 + 0] + dx;
                var m1y = mPrep[i * 10 + 1] + dy;
                var m2x = mPrep[i * 10 + 2] + dx;
                var m2y = mPrep[i * 10 + 3] + dy;

                for (int j = 0; j < sCount; j++)
                {
                    var sMin = horizontal ? sPrep[j * 10 + 8] : sPrep[j * 10 + 6];
                    var sMax = horizontal ? sPrep[j * 10 + 9] : sPrep[j * 10 + 7];

                    // Test moving vertex 1 against stationary edge j
                    var mv1 = horizontal ? m1y : m1x;
                    if (mv1 >= sMin - eps && mv1 <= sMax + eps)
                    {
                        var d = RayEdgeLean(m1x, m1y, sPrep, j, direction, eps);
                        if (d < minDist) minDist = d;
                    }

                    // Test moving vertex 2 against stationary edge j
                    var mv2 = horizontal ? m2y : m2x;
                    if (mv2 >= sMin - eps && mv2 <= sMax + eps)
                    {
                        var d = RayEdgeLean(m2x, m2y, sPrep, j, direction, eps);
                        if (d < minDist) minDist = d;
                    }
                }
            }

            // ── Reverse Pass: stationary vertices vs moving edges ─────
            for (int i = 0; i < sCount; i++)
            {
                var s1x = sPrep[i * 10 + 0];
                var s1y = sPrep[i * 10 + 1];
                var s2x = sPrep[i * 10 + 2];
                var s2y = sPrep[i * 10 + 3];

                for (int j = 0; j < mCount; j++)
                {
                    var mMin = horizontal ? (mPrep[j * 10 + 8] + dy) : (mPrep[j * 10 + 6] + dx);
                    var mMax = horizontal ? (mPrep[j * 10 + 9] + dy) : (mPrep[j * 10 + 7] + dx);

                    // Test stationary vertex 1 against moving edge j
                    var sv1 = horizontal ? s1y : s1x;
                    if (sv1 >= mMin - eps && sv1 <= mMax + eps)
                    {
                        var d = RayEdgeLeanMoving(s1x, s1y, mPrep, j, dx, dy, oppDir, eps);
                        if (d < minDist) minDist = d;
                    }

                    // Test stationary vertex 2 against moving edge j
                    var sv2 = horizontal ? s2y : s2x;
                    if (sv2 >= mMin - eps && sv2 <= mMax + eps)
                    {
                        var d = RayEdgeLeanMoving(s2x, s2y, mPrep, j, dx, dy, oppDir, eps);
                        if (d < minDist) minDist = d;
                    }
                }
            }

            return minDist;
        }

        private static double RayEdgeLean(
            double vx, double vy,
            ArrayView1D<double, Stride1D.Dense> sPrep, int j,
            int direction, double eps)
        {
            var p1x = sPrep[j * 10 + 0];
            var p1y = sPrep[j * 10 + 1];
            var p2x = sPrep[j * 10 + 2];
            var p2y = sPrep[j * 10 + 3];

            if (direction >= 2) // Horizontal (Left=2, Right=3)
            {
                var invDy = sPrep[j * 10 + 5];
                if (invDy == 0) return double.MaxValue;

                var t = (vy - p1y) * invDy;
                if (t < -eps || t > 1.0 + eps) return double.MaxValue;

                var ix = p1x + t * (p2x - p1x);
                var dist = (direction == 2) ? (vx - ix) : (ix - vx);

                if (dist > eps) return dist;
                return (dist >= -eps) ? 0.0 : double.MaxValue;
            }
            else // Vertical (Up=0, Down=1)
            {
                var invDx = sPrep[j * 10 + 4];
                if (invDx == 0) return double.MaxValue;

                var t = (vx - p1x) * invDx;
                if (t < -eps || t > 1.0 + eps) return double.MaxValue;

                var iy = p1y + t * (p2y - p1y);
                var dist = (direction == 1) ? (vy - iy) : (iy - vy);

                if (dist > eps) return dist;
                return (dist >= -eps) ? 0.0 : double.MaxValue;
            }
        }

        private static double RayEdgeLeanMoving(
            double vx, double vy,
            ArrayView1D<double, Stride1D.Dense> mPrep, int j,
            double dx, double dy, int direction, double eps)
        {
            var p1x = mPrep[j * 10 + 0] + dx;
            var p1y = mPrep[j * 10 + 1] + dy;
            var p2x = mPrep[j * 10 + 2] + dx;
            var p2y = mPrep[j * 10 + 3] + dy;

            if (direction >= 2) // Horizontal
            {
                var invDy = mPrep[j * 10 + 5];
                if (invDy == 0) return double.MaxValue;

                var t = (vy - p1y) * invDy;
                if (t < -eps || t > 1.0 + eps) return double.MaxValue;

                var ix = p1x + t * (p2x - p1x);
                var dist = (direction == 2) ? (vx - ix) : (ix - vx);

                if (dist > eps) return dist;
                return (dist >= -eps) ? 0.0 : double.MaxValue;
            }
            else // Vertical
            {
                var invDx = mPrep[j * 10 + 4];
                if (invDx == 0) return double.MaxValue;

                var t = (vx - p1x) * invDx;
                if (t < -eps || t > 1.0 + eps) return double.MaxValue;

                var iy = p1y + t * (p2y - p1y);
                var dist = (direction == 1) ? (vy - iy) : (iy - vy);

                if (dist > eps) return dist;
                return (dist >= -eps) ? 0.0 : double.MaxValue;
            }
        }

        public void Dispose()
        {
            _gpuStationaryRaw?.Dispose();
            _gpuStationaryPrep?.Dispose();
            _gpuMovingRaw?.Dispose();
            _gpuMovingPrep?.Dispose();
            _gpuOffsets?.Dispose();
            _gpuResults?.Dispose();
            _gpuDirs?.Dispose();
            _accelerator?.Dispose();
            _context?.Dispose();
        }
    }
}