package kimi_linear

import (
	"context"
	"fmt"

	"makarna/pkg/backend/cpu"
	"makarna/pkg/backend/cpu/nn"
	"makarna/pkg/compute"
	"makarna/pkg/model"
	"makarna/pkg/tensor"
)

func (m *Model) Forward(ctx context.Context, input tensor.Tensor, positions tensor.Tensor, kvCache model.KVCache) (tensor.Tensor, error) {
	cfg := m.config
	seqLen := input.Shape()[0]

	ids := nn.ParseTokenIDs(input)
	posArr := nn.ParsePositions(positions, seqLen)
	dispatcher := compute.DispatcherFromContext(ctx)
	scratchSet := compute.ScratchSetFromContext(ctx)
	baseScratch := compute.ScratchFromContext(ctx)
	cpuMoE := compute.CPUMoEFromContext(ctx)

	// Track GPU allocations for cleanup at end of forward pass
	var gpuAllocations []*compute.Activation
	defer func() {
		for _, act := range gpuAllocations {
			compute.FreeActivation(act)
		}
	}()

	hidden, err := compute.HybridTokenEmbedding(ids, m.tokenEmb, cfg.HiddenSize, dispatcher)
	if err != nil {
		return nil, fmt.Errorf("embedding: %w", err)
	}

	var cache *KimiCache
	if kvCache != nil {
		if c, ok := AsKimiCache(kvCache); ok {
			cache = c
		}
	}
	if cache == nil {
		kdaCfg, _ := parseLinearAttnConfig(cfg)
		cache, err = NewKimiCache(cfg.NumLayers, m.kdaNumHeads, m.kdaHeadDim, kdaCfg.ShortConvKernel, m.mlaNumHeads, m.mlaKHeadDim, m.mlaVHeadDim)
		if err != nil {
			return nil, err
		}
	}

	eps := float32(cfg.RMSNormEps)
	if eps == 0 {
		eps = 1e-5
	}

	for i, layer := range m.layers {
		compCtx := compute.NewContext(dispatcher, i)
		compCtx.CPUMoE = cpuMoE
		if p := compCtx.Placement(); p.Type == tensor.CUDA {
			var layerScratch *compute.ScratchSpace
			if scratchSet != nil {
				layerScratch = scratchSet.Scratch(p.GPU)
			} else if baseScratch != nil && baseScratch.GPU() == p.GPU {
				layerScratch = baseScratch
			}
			if layerScratch != nil {
				layerScratch.Reset()
			}
			compCtx.Scratch = layerScratch
		}

		allocAct := func(shape tensor.Shape) (*compute.Activation, error) {
			if compCtx.Scratch != nil && compCtx.Placement().Type == tensor.CUDA {
				if act, err := compCtx.Scratch.GetTensor(shape, tensor.Float32); err == nil {
					return act, nil
				}
			}
			act, err := compute.NewActivation(shape, compCtx.Placement())
			if err == nil && act != nil && compCtx.Placement().Type == tensor.CUDA {
				// Track GPU allocations that are not from scratch
				gpuAllocations = append(gpuAllocations, act)
			}
			return act, err
		}

		// Ensure activations are on the target device for this layer.
		if _, err := hidden.EnsureOn(compCtx.Placement()); err != nil {
			return nil, err
		}

		// Save residual BEFORE layernorm (pre-norm architecture)
		residualAct, err := allocAct(tensor.Shape{seqLen, cfg.HiddenSize})
		if err != nil {
			return nil, err
		}
		if err := compute.HybridCopy(compCtx, residualAct, hidden); err != nil {
			return nil, err
		}

		if layer.inputLayernorm == nil {
			return nil, fmt.Errorf("layer %d: missing input_layernorm", i)
		}
		if err := compute.HybridRMSNorm(compCtx, hidden, layer.inputLayernorm, eps); err != nil {
			return nil, fmt.Errorf("layer %d: attn norm: %w", i, err)
		}

		attnOutAct, err := allocAct(tensor.Shape{seqLen, cfg.HiddenSize})
		if err != nil {
			return nil, err
		}

		switch layer.kind {
		case layerKindKDA:
			if layer.kdaQProj == nil || layer.kdaKProj == nil || layer.kdaVProj == nil || layer.kdaOProj == nil {
				return nil, fmt.Errorf("layer %d: missing KDA projections", i)
			}
			if layer.kdaQConv == nil || layer.kdaKConv == nil || layer.kdaVConv == nil {
				return nil, fmt.Errorf("layer %d: missing KDA conv weights", i)
			}
			if layer.kdaFAProj == nil || layer.kdaFBProj == nil || layer.kdaBProj == nil {
				return nil, fmt.Errorf("layer %d: missing KDA gate/beta projections", i)
			}
			if layer.kdaALog == nil || layer.kdaDTBias == nil {
				return nil, fmt.Errorf("layer %d: missing KDA A_log/dt_bias", i)
			}
			if layer.kdaGAProj == nil || layer.kdaGBProj == nil {
				return nil, fmt.Errorf("layer %d: missing KDA o_norm gate projections", i)
			}
			kdaCfg, _ := parseLinearAttnConfig(m.config)
			convQ, convK, convV, err := cache.ConvStates(i, compCtx.Placement())
			if err != nil {
				return nil, err
			}
			stT, err := cache.RecurrentState(i, compCtx.Placement())
			if err != nil {
				return nil, err
			}
			if err := compute.HybridKDA(
				compCtx,
				hidden,
				layer.kdaQProj, layer.kdaKProj, layer.kdaVProj,
				layer.kdaQConv, layer.kdaKConv, layer.kdaVConv,
				layer.kdaFAProj, layer.kdaFBProj, layer.kdaBProj,
				layer.kdaALog,
				layer.kdaDTBias,
				layer.kdaGAProj, layer.kdaGBProj,
				layer.kdaONorm,
				layer.kdaOProj,
				convQ, convK, convV,
				stT,
				seqLen, m.kdaNumHeads, m.kdaHeadDim, kdaCfg.ShortConvKernel,
				eps,
				attnOutAct,
			); err != nil {
				return nil, fmt.Errorf("layer %d: kda: %w", i, err)
			}

		case layerKindFull:
			if layer.mlaQProj == nil || layer.mlaKVAProjWithMQA == nil || layer.mlaKVALayernorm == nil || layer.mlaKVBProj == nil || layer.mlaOProj == nil {
				return nil, fmt.Errorf("layer %d: missing MLA weights", i)
			}
			mlaCfg, _ := parseMLAConfig(m.config)
			qkNope := mlaCfg.QKNopeHeadDim
			qkRope := mlaCfg.QKRopeHeadDim
			vDim := mlaCfg.VHeadDim
			kvARank := mlaCfg.KVLoraRank
			if kvARank <= 0 || qkNope <= 0 || qkRope <= 0 || vDim <= 0 {
				return nil, fmt.Errorf("layer %d: invalid MLA config", i)
			}
			if qkNope+qkRope != m.mlaKHeadDim {
				return nil, fmt.Errorf("layer %d: mla head dim mismatch", i)
			}
			if vDim != m.mlaVHeadDim {
				return nil, fmt.Errorf("layer %d: mla v dim mismatch", i)
			}

			qAct, err := compute.NewActivation(tensor.Shape{seqLen, m.mlaNumHeads * m.mlaKHeadDim}, tensor.DevicePlacement{Type: tensor.CPU, GPU: -1})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridLinear(compCtx, hidden, layer.mlaQProj, qAct); err != nil {
				return nil, fmt.Errorf("layer %d: mla q_proj: %w", i, err)
			}
			qCPU, _ := qAct.AsCPU()

			kvAAct, err := compute.NewActivation(tensor.Shape{seqLen, kvARank + qkRope}, tensor.DevicePlacement{Type: tensor.CPU, GPU: -1})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridLinear(compCtx, hidden, layer.mlaKVAProjWithMQA, kvAAct); err != nil {
				return nil, fmt.Errorf("layer %d: mla kv_a_proj: %w", i, err)
			}
			kvACPU, _ := kvAAct.AsCPU()

			kvPass := cpu.NewTensor(tensor.Shape{seqLen, kvARank}, nil)
			for t := 0; t < seqLen; t++ {
				copy(kvPass.DataFloat32()[t*kvARank:(t+1)*kvARank], kvACPU.DataFloat32()[t*(kvARank+qkRope):t*(kvARank+qkRope)+kvARank])
			}
			kvPassAct := compute.NewActivationFrom(kvPass)
			if compCtx.IsGPU() {
				if _, err := kvPassAct.EnsureOn(compCtx.Placement()); err != nil {
					return nil, err
				}
			}
			if err := compute.HybridRMSNorm(compCtx, kvPassAct, layer.mlaKVALayernorm, eps); err != nil {
				return nil, fmt.Errorf("layer %d: mla kv_a_layernorm: %w", i, err)
			}

			kvBAct, err := allocAct(tensor.Shape{seqLen, m.mlaNumHeads * (qkNope + vDim)})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridLinear(compCtx, kvPassAct, layer.mlaKVBProj, kvBAct); err != nil {
				return nil, fmt.Errorf("layer %d: mla kv_b_proj: %w", i, err)
			}
			kvBCPU, _ := kvBAct.AsCPU()

			kStep := cpu.NewTensor(tensor.Shape{seqLen, m.mlaNumHeads * m.mlaKHeadDim}, nil)
			vStep := cpu.NewTensor(tensor.Shape{seqLen, m.mlaNumHeads * m.mlaVHeadDim}, nil)
			for t := 0; t < seqLen; t++ {
				kRotBase := t*(kvARank+qkRope) + kvARank
				kRot := kvACPU.DataFloat32()[kRotBase : kRotBase+qkRope]
				for h := 0; h < m.mlaNumHeads; h++ {
					srcBase := t*(m.mlaNumHeads*(qkNope+vDim)) + h*(qkNope+vDim)
					copy(kStep.DataFloat32()[t*(m.mlaNumHeads*m.mlaKHeadDim)+h*m.mlaKHeadDim:t*(m.mlaNumHeads*m.mlaKHeadDim)+h*m.mlaKHeadDim+qkNope], kvBCPU.DataFloat32()[srcBase:srcBase+qkNope])
					copy(kStep.DataFloat32()[t*(m.mlaNumHeads*m.mlaKHeadDim)+h*m.mlaKHeadDim+qkNope:t*(m.mlaNumHeads*m.mlaKHeadDim)+h*m.mlaKHeadDim+qkNope+qkRope], kRot)
					copy(vStep.DataFloat32()[t*(m.mlaNumHeads*m.mlaVHeadDim)+h*m.mlaVHeadDim:t*(m.mlaNumHeads*m.mlaVHeadDim)+h*m.mlaVHeadDim+vDim], kvBCPU.DataFloat32()[srcBase+qkNope:srcBase+qkNope+vDim])
				}
			}

			startPos, err := cache.AppendFull(i, kStep, vStep)
			if err != nil {
				return nil, fmt.Errorf("layer %d: cache append: %w", i, err)
			}
			fullK, fullV, _, ok := cache.FullKV(i)
			if !ok {
				return nil, fmt.Errorf("layer %d: full kv missing", i)
			}

			attnCore := cpu.NewTensor(tensor.Shape{seqLen, m.mlaNumHeads * m.mlaVHeadDim}, nil)
			if err := nn.CausalAttentionCachedKV(qCPU, fullK, fullV, attnCore, m.mlaNumHeads, m.mlaNumHeads, m.mlaKHeadDim, m.mlaVHeadDim, startPos); err != nil {
				return nil, fmt.Errorf("layer %d: mla attention: %w", i, err)
			}
			attnCoreAct := compute.NewActivationFrom(attnCore)
			if compCtx.IsGPU() {
				if _, err := attnCoreAct.EnsureOn(compCtx.Placement()); err != nil {
					return nil, err
				}
			}
			if err := compute.HybridLinear(compCtx, attnCoreAct, layer.mlaOProj, attnOutAct); err != nil {
				return nil, fmt.Errorf("layer %d: mla o_proj: %w", i, err)
			}

		default:
			return nil, fmt.Errorf("layer %d: unknown layer kind", i)
		}

		if err := compute.HybridAdd(compCtx, attnOutAct, residualAct); err != nil {
			return nil, err
		}
		hidden = attnOutAct

		// Save MLP residual BEFORE post_attention_layernorm (pre-norm architecture)
		mlpResidualAct, err := allocAct(tensor.Shape{seqLen, cfg.HiddenSize})
		if err != nil {
			return nil, err
		}
		if err := compute.HybridCopy(compCtx, mlpResidualAct, hidden); err != nil {
			return nil, err
		}

		if layer.postAttnNorm == nil {
			return nil, fmt.Errorf("layer %d: missing post_attention_layernorm", i)
		}
		if err := compute.HybridRMSNorm(compCtx, hidden, layer.postAttnNorm, eps); err != nil {
			return nil, fmt.Errorf("layer %d: post attn norm: %w", i, err)
		}
		moeCfg, _ := parseMoEConfig(m.config)
		useMoE := layer.moeGateW != nil && len(layer.moeW1) > 0 && len(layer.moeW2) > 0 && len(layer.moeW3) > 0
		if useMoE {
			first := moeCfg.FirstKDenseReplace
			if first <= 0 {
				first = 1
			}
			freq := moeCfg.LayerFreq
			if freq <= 0 {
				freq = 1
			}
			if i < first || (i-first)%freq != 0 {
				useMoE = false
			}
		}

		if useMoE {
			moeOutAct, err := allocAct(tensor.Shape{seqLen, cfg.HiddenSize})
			if err != nil {
				return nil, err
			}
			moeWeights := &compute.MoEWeights{
				GateW:      layer.moeGateW,
				GateBias:   layer.moeGateBias,
				W1:         layer.moeW1,
				W2:         layer.moeW2,
				W3:         layer.moeW3,
				SharedGate: layer.moeSharedGate,
				SharedUp:   layer.moeSharedUp,
				SharedDown: layer.moeSharedDown,
			}
			moeCfgCompute := compute.MoEConfig{
				NumExperts:           moeCfg.NumExperts,
				TopK:                 moeCfg.TopK,
				IntermediateSize:     moeCfg.IntermediateSize,
				RouterActivationFunc: moeCfg.RouterActivationFunc,
				UseGroupedTopK:       moeCfg.UseGroupedTopK,
				NumExpertGroup:       moeCfg.NumExpertGroup,
				TopKGroup:            moeCfg.TopKGroup,
				Renormalize:          moeCfg.Renormalize,
				RoutedScalingFactor:  moeCfg.RoutedScalingFactor,
				NumSharedExperts:     moeCfg.NumSharedExperts,
			}
			if err := compute.HybridMoE(compCtx, hidden, moeWeights, moeCfgCompute, moeOutAct); err != nil {
				return nil, fmt.Errorf("layer %d: moe: %w", i, err)
			}
			if err := compute.HybridAdd(compCtx, moeOutAct, mlpResidualAct); err != nil {
				return nil, err
			}
			hidden = moeOutAct
		} else {
			if layer.mlpGateProj == nil || layer.mlpUpProj == nil || layer.mlpDownProj == nil {
				return nil, fmt.Errorf("layer %d: missing MLP weights", i)
			}
			gateAct, err := allocAct(tensor.Shape{seqLen, cfg.Intermediate})
			if err != nil {
				return nil, err
			}
			upAct, err := allocAct(tensor.Shape{seqLen, cfg.Intermediate})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridLinear(compCtx, hidden, layer.mlpGateProj, gateAct); err != nil {
				return nil, fmt.Errorf("layer %d: mlp gate: %w", i, err)
			}
			if err := compute.HybridLinear(compCtx, hidden, layer.mlpUpProj, upAct); err != nil {
				return nil, fmt.Errorf("layer %d: mlp up: %w", i, err)
			}
			act, err := allocAct(tensor.Shape{seqLen, cfg.Intermediate})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridSwiGLU(compCtx, gateAct, upAct, act); err != nil {
				return nil, fmt.Errorf("layer %d: swiglu: %w", i, err)
			}
			mlpOut, err := allocAct(tensor.Shape{seqLen, cfg.HiddenSize})
			if err != nil {
				return nil, err
			}
			if err := compute.HybridLinear(compCtx, act, layer.mlpDownProj, mlpOut); err != nil {
				return nil, fmt.Errorf("layer %d: mlp down: %w", i, err)
			}
			if err := compute.HybridAdd(compCtx, mlpOut, mlpResidualAct); err != nil {
				return nil, err
			}
			hidden = mlpOut
		}
	}

	cache.Commit(seqLen)

	finalCtx := compute.NewContext(dispatcher, len(m.layers)-1)
	if m.norm == nil {
		return nil, fmt.Errorf("missing model.norm.weight")
	}
	if err := compute.HybridRMSNorm(finalCtx, hidden, m.norm, eps); err != nil {
		return nil, fmt.Errorf("final norm: %w", err)
	}

	logits := compute.NewActivationFrom(cpu.NewTensor(tensor.Shape{seqLen, cfg.VocabSize}, nil))
	outputW := m.output
	if outputW == nil {
		outputW = m.tokenEmb
	}
	if outputW == nil {
		return nil, fmt.Errorf("missing lm_head.weight and embed_tokens.weight")
	}
	if err := compute.HybridLinear(finalCtx, hidden, outputW, logits); err != nil {
		return nil, fmt.Errorf("lm head: %w", err)
	}

	_ = posArr
	return logits.Tensor(), nil
}