// Copyright 2025 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"bytes"
	"fmt"
	"log"
	"sort"
	"strings"
)

const simdMachineOpsTmpl = `
package main

func simdAMD64Ops(v11, v21, v2k, vkv, v2kv, v2kk, v31, v3kv, vgpv, vgp, vfpv, vfpkv, w11, w21, w2k, wkw, w2kw, w2kk, w31, w3kw, wgpw, wgp, wfpw, wfpkw,
	wkwload, v21load, v31load, v11load, w21load, w31load, w2kload, w2kwload, w11load, w3kwload, w2kkload, v31x0AtIn2 regInfo) []opData {
	return []opData{
{{- range .OpsData }}
		{name: "{{.OpName}}", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", commutative: {{.Comm}}, typ: "{{.Type}}", resultInArg0: {{.ResultInArg0}}},
{{- end }}
{{- range .OpsDataImm }}
		{name: "{{.OpName}}", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", aux: "UInt8", commutative: {{.Comm}}, typ: "{{.Type}}", resultInArg0: {{.ResultInArg0}}},
{{- end }}
{{- range .OpsDataLoad}}
		{name: "{{.OpName}}", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", commutative: {{.Comm}}, typ: "{{.Type}}", aux: "SymOff", symEffect: "Read", resultInArg0: {{.ResultInArg0}}},
{{- end}}
{{- range .OpsDataImmLoad}}
		{name: "{{.OpName}}", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", commutative: {{.Comm}}, typ: "{{.Type}}", aux: "SymValAndOff", symEffect: "Read", resultInArg0: {{.ResultInArg0}}},
{{- end}}
{{- range .OpsDataMerging }}
		{name: "{{.OpName}}Merging", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", commutative: false, typ: "{{.Type}}", resultInArg0: true},
{{- end }}
{{- range .OpsDataImmMerging }}
		{name: "{{.OpName}}Merging", argLength: {{.OpInLen}}, reg: {{.RegInfo}}, asm: "{{.Asm}}", aux: "UInt8", commutative: false, typ: "{{.Type}}", resultInArg0: true},
{{- end }}
	}
}
`

// writeSIMDMachineOps generates the machine ops and writes it to simdAMD64ops.go
// within the specified directory.
func writeSIMDMachineOps(ops []Operation) *bytes.Buffer {
	t := templateOf(simdMachineOpsTmpl, "simdAMD64Ops")
	buffer := new(bytes.Buffer)
	buffer.WriteString(generatedHeader)

	type opData struct {
		OpName       string
		Asm          string
		OpInLen      int
		RegInfo      string
		Comm         bool
		Type         string
		ResultInArg0 bool
	}
	type machineOpsData struct {
		OpsData           []opData
		OpsDataImm        []opData
		OpsDataLoad       []opData
		OpsDataImmLoad    []opData
		OpsDataMerging    []opData
		OpsDataImmMerging []opData
	}

	regInfoSet := map[string]bool{
		"v11": true, "v21": true, "v2k": true, "v2kv": true, "v2kk": true, "vkv": true, "v31": true, "v3kv": true, "vgpv": true, "vgp": true, "vfpv": true, "vfpkv": true,
		"w11": true, "w21": true, "w2k": true, "w2kw": true, "w2kk": true, "wkw": true, "w31": true, "w3kw": true, "wgpw": true, "wgp": true, "wfpw": true, "wfpkw": true,
		"wkwload": true, "v21load": true, "v31load": true, "v11load": true, "w21load": true, "w31load": true, "w2kload": true, "w2kwload": true, "w11load": true,
		"w3kwload": true, "w2kkload": true, "v31x0AtIn2": true}
	opsData := make([]opData, 0)
	opsDataImm := make([]opData, 0)
	opsDataLoad := make([]opData, 0)
	opsDataImmLoad := make([]opData, 0)
	opsDataMerging := make([]opData, 0)
	opsDataImmMerging := make([]opData, 0)

	// Determine the "best" version of an instruction to use
	best := make(map[string]Operation)
	var mOpOrder []string
	countOverrides := func(s []Operand) int {
		a := 0
		for _, o := range s {
			if o.OverwriteBase != nil {
				a++
			}
		}
		return a
	}
	for _, op := range ops {
		_, _, maskType, _, gOp := op.shape()
		asm := machineOpName(maskType, gOp)
		other, ok := best[asm]
		if !ok {
			best[asm] = op
			mOpOrder = append(mOpOrder, asm)
			continue
		}
		// see if "op" is better than "other"
		if countOverrides(op.In)+countOverrides(op.Out) < countOverrides(other.In)+countOverrides(other.Out) {
			best[asm] = op
		}
	}

	regInfoErrs := make([]error, 0)
	regInfoMissing := make(map[string]bool, 0)
	for _, asm := range mOpOrder {
		op := best[asm]
		shapeIn, shapeOut, maskType, _, gOp := op.shape()

		// TODO: all our masked operations are now zeroing, we need to generate machine ops with merging masks, maybe copy
		// one here with a name suffix "Merging". The rewrite rules will need them.
		makeRegInfo := func(op Operation, mem memShape) (string, error) {
			regInfo, err := op.regShape(mem)
			if err != nil {
				panic(err)
			}
			regInfo, err = rewriteVecAsScalarRegInfo(op, regInfo)
			if err != nil {
				if mem == NoMem || mem == InvalidMem {
					panic(err)
				}
				return "", err
			}
			if regInfo == "v01load" {
				regInfo = "vload"
			}
			// Makes AVX512 operations use upper registers
			if strings.Contains(op.CPUFeature, "AVX512") {
				regInfo = strings.ReplaceAll(regInfo, "v", "w")
			}
			if _, ok := regInfoSet[regInfo]; !ok {
				regInfoErrs = append(regInfoErrs, fmt.Errorf("unsupported register constraint, please update the template and AMD64Ops.go: %s.  Op is %s", regInfo, op))
				regInfoMissing[regInfo] = true
			}
			return regInfo, nil
		}
		regInfo, err := makeRegInfo(op, NoMem)
		if err != nil {
			panic(err)
		}
		var outType string
		if shapeOut == OneVregOut || shapeOut == OneVregOutAtIn || gOp.Out[0].OverwriteClass != nil {
			// If class overwrite is happening, that's not really a mask but a vreg.
			outType = fmt.Sprintf("Vec%d", *gOp.Out[0].Bits)
		} else if shapeOut == OneGregOut {
			outType = gOp.GoType() // this is a straight Go type, not a VecNNN type
		} else if shapeOut == OneKmaskOut {
			outType = "Mask"
		} else {
			panic(fmt.Errorf("simdgen does not recognize this output shape: %d", shapeOut))
		}
		resultInArg0 := false
		if shapeOut == OneVregOutAtIn {
			resultInArg0 = true
		}
		var memOpData *opData
		regInfoMerging := regInfo
		hasMerging := false
		if op.MemFeatures != nil && *op.MemFeatures == "vbcst" {
			// Right now we only have vbcst case
			// Make a full vec memory variant.
			opMem := rewriteLastVregToMem(op)
			regInfo, err := makeRegInfo(opMem, VregMemIn)
			if err != nil {
				// Just skip it if it's non nill.
				// an error could be triggered by [checkVecAsScalar].
				// TODO: make [checkVecAsScalar] aware of mem ops.
				if *Verbose {
					log.Printf("Seen error: %e", err)
				}
			} else {
				memOpData = &opData{asm + "load", gOp.Asm, len(gOp.In) + 1, regInfo, false, outType, resultInArg0}
			}
		}
		hasMerging = gOp.hasMaskedMerging(maskType, shapeOut)
		if hasMerging && !resultInArg0 {
			// We have to copy the slice here becasue the sort will be visible from other
			// aliases when no reslicing is happening.
			newIn := make([]Operand, len(op.In), len(op.In)+1)
			copy(newIn, op.In)
			op.In = newIn
			op.In = append(op.In, op.Out[0])
			op.sortOperand()
			regInfoMerging, err = makeRegInfo(op, NoMem)
			if err != nil {
				panic(err)
			}
		}

		if shapeIn == OneImmIn || shapeIn == OneKmaskImmIn {
			opsDataImm = append(opsDataImm, opData{asm, gOp.Asm, len(gOp.In), regInfo, gOp.Commutative, outType, resultInArg0})
			if memOpData != nil {
				if *op.MemFeatures != "vbcst" {
					panic("simdgen only knows vbcst for mem ops for now")
				}
				opsDataImmLoad = append(opsDataImmLoad, *memOpData)
			}
			if hasMerging {
				mergingLen := len(gOp.In)
				if !resultInArg0 {
					mergingLen++
				}
				opsDataImmMerging = append(opsDataImmMerging, opData{asm, gOp.Asm, mergingLen, regInfoMerging, gOp.Commutative, outType, resultInArg0})
			}
		} else {
			opsData = append(opsData, opData{asm, gOp.Asm, len(gOp.In), regInfo, gOp.Commutative, outType, resultInArg0})
			if memOpData != nil {
				if *op.MemFeatures != "vbcst" {
					panic("simdgen only knows vbcst for mem ops for now")
				}
				opsDataLoad = append(opsDataLoad, *memOpData)
			}
			if hasMerging {
				mergingLen := len(gOp.In)
				if !resultInArg0 {
					mergingLen++
				}
				opsDataMerging = append(opsDataMerging, opData{asm, gOp.Asm, mergingLen, regInfoMerging, gOp.Commutative, outType, resultInArg0})
			}
		}
	}
	if len(regInfoErrs) != 0 {
		for _, e := range regInfoErrs {
			log.Printf("Errors: %e\n", e)
		}
		panic(fmt.Errorf("these regInfo unseen: %v", regInfoMissing))
	}
	sort.Slice(opsData, func(i, j int) bool {
		return compareNatural(opsData[i].OpName, opsData[j].OpName) < 0
	})
	sort.Slice(opsDataImm, func(i, j int) bool {
		return compareNatural(opsDataImm[i].OpName, opsDataImm[j].OpName) < 0
	})
	sort.Slice(opsDataLoad, func(i, j int) bool {
		return compareNatural(opsDataLoad[i].OpName, opsDataLoad[j].OpName) < 0
	})
	sort.Slice(opsDataImmLoad, func(i, j int) bool {
		return compareNatural(opsDataImmLoad[i].OpName, opsDataImmLoad[j].OpName) < 0
	})
	sort.Slice(opsDataMerging, func(i, j int) bool {
		return compareNatural(opsDataMerging[i].OpName, opsDataMerging[j].OpName) < 0
	})
	sort.Slice(opsDataImmMerging, func(i, j int) bool {
		return compareNatural(opsDataImmMerging[i].OpName, opsDataImmMerging[j].OpName) < 0
	})
	err := t.Execute(buffer, machineOpsData{opsData, opsDataImm, opsDataLoad, opsDataImmLoad,
		opsDataMerging, opsDataImmMerging})
	if err != nil {
		panic(fmt.Errorf("failed to execute template: %w", err))
	}

	return buffer
}