//go:build cuda

package compute

import (
	"fmt"
	"unsafe"

	"makarna/pkg/backend/cpu"
	"makarna/pkg/backend/cpu/nn"
	"makarna/pkg/backend/cuda"
	"makarna/pkg/backend/device"
	"makarna/pkg/tensor"
)

func HybridTokenEmbedding(ids []int, tokenEmb tensor.Tensor, hiddenSize int, dispatcher *device.DeviceDispatcher) (*Activation, error) {
	seqLen := len(ids)

	// Fast-path: single-token decode, first layer on GPU, embedding weights are quantized.
	// We dequantize only the selected row directly on GPU to avoid CPU dequant + H2D copy.
	if seqLen == 1 && dispatcher != nil {
		p0 := dispatcher.LayerPlacement(0).Normalize()
		if p0.Type == tensor.CUDA && cuda.Available() {
			gpu := p0.GPU
			if gpu < 0 {
				gpu = 0
			}
			if embCPU, ok := tokenEmb.(*cpu.Tensor); ok {
				dtype := embCPU.DType()
				blocksPerDim := hiddenSize / 256
				if blocksPerDim > 0 && hiddenSize%256 == 0 {
					cache := GetWeightCache(gpu)
					wKey := fmt.Sprintf("tok_emb_%p", embCPU)
					gpuW, ok2 := cache.Get(wKey)
					var err error
					if !ok2 {
						gpuW, err = cache.Upload(wKey, embCPU)
						if err != nil {
							return nil, err
						}
					}

					var bytesPerBlock int
					switch dtype {
					case tensor.Q8_K:
						bytesPerBlock = 292
					case tensor.Q5_K:
						bytesPerBlock = 176
					case tensor.Q4_K:
						bytesPerBlock = 144
					case tensor.Q2_K:
						bytesPerBlock = 84
					case tensor.Q3_K:
						bytesPerBlock = 110
					case tensor.Q6_K:
						bytesPerBlock = 210
					default:
						bytesPerBlock = 0
					}

					if bytesPerBlock > 0 {
						hiddenGPU, err2 := cuda.NewTensor(tensor.Shape{1, hiddenSize}, tensor.Float32, gpu)
						if err2 == nil {
							id := ids[0]
							rowOff := uintptr(id * blocksPerDim * bytesPerBlock)
							rowPtr := unsafe.Pointer(uintptr(gpuW) + rowOff)
							outPtr := hiddenGPU.Data().(unsafe.Pointer)
							switch dtype {
							case tensor.Q8_K:
								err2 = cuda.DequantQ8K(rowPtr, outPtr, blocksPerDim, gpu)
							case tensor.Q5_K:
								err2 = cuda.DequantQ5K(rowPtr, outPtr, blocksPerDim, gpu)
							case tensor.Q4_K:
								err2 = cuda.DequantQ4K(rowPtr, outPtr, blocksPerDim, gpu)
							case tensor.Q2_K:
								err2 = cuda.DequantQ2K(rowPtr, outPtr, blocksPerDim, gpu)
							case tensor.Q3_K:
								err2 = cuda.DequantQ3K(rowPtr, outPtr, blocksPerDim, gpu)
							case tensor.Q6_K:
								err2 = cuda.DequantQ6K(rowPtr, outPtr, blocksPerDim, gpu)
							}
							if err2 == nil {
								return NewActivationFrom(hiddenGPU), nil
							}
						}
					}
				}
			}
		}
	}

	// Generic CPU embedding.
	embCPU, err := ToCPU(tokenEmb)
	if err != nil {
		return nil, err
	}
	hiddenCPU := cpu.NewTensor(tensor.Shape{seqLen, hiddenSize}, nil)
	if err := nn.Embedding(ids, embCPU, hiddenCPU); err != nil {
		return nil, err
	}
	return NewActivationFrom(hiddenCPU), nil
}