//go:build ignore
// +build ignore

package main

import (
	"bytes"
	"go/format"
	"io"
	"log"
	"os"
	"os/exec"
)

// Running this generator requires addchain v0.4.0, which can be installed with
//
//   go install github.com/mmcloughlin/addchain/cmd/addchain@v0.4.0
//

func main() {
	tmplAddchainFile, err := os.CreateTemp("", "addchain-template")
	if err != nil {
		log.Fatal(err)
	}
	defer os.Remove(tmplAddchainFile.Name())
	if _, err := io.WriteString(tmplAddchainFile, tmplAddchain); err != nil {
		log.Fatal(err)
	}
	if err := tmplAddchainFile.Close(); err != nil {
		log.Fatal(err)
	}
	log.Printf("Generating gfp_invert.go...")
	f, err := os.CreateTemp("", "addchain-gfp")
	if err != nil {
		log.Fatal(err)
	}
	defer os.Remove(f.Name())
	cmd := exec.Command("addchain", "search", "0xb640000002a3a6f1d603ab4ff58ec74521f2934b1a7aeedbe56f9b27e351457b")
	cmd.Stderr = os.Stderr
	cmd.Stdout = f
	if err := cmd.Run(); err != nil {
		log.Fatal(err)
	}
	if err := f.Close(); err != nil {
		log.Fatal(err)
	}
	cmd = exec.Command("addchain", "gen", "-tmpl", tmplAddchainFile.Name(), f.Name())
	cmd.Stderr = os.Stderr
	out, err := cmd.Output()
	if err != nil {
		log.Fatal(err)
	}
	out = bytes.Replace(out, []byte("Element"), []byte("gfP"), -1)
	out, err = format.Source(out)
	if err != nil {
		log.Fatal(err)
	}
	if err := os.WriteFile("gfp_invert.go", out, 0644); err != nil {
		log.Fatal(err)
	}
}

const tmplAddchain = `// Code generated by {{ .Meta.Name }}. DO NOT EDIT.
package bn256
// Invert sets e = 1/x, and returns e.
//
// If x == 0, Invert returns e = 0.
func (e *Element) Invert(x *Element) *Element {
	// Inversion is implemented as exponentiation with exponent p − 2.
	// The sequence of {{ .Ops.Adds }} multiplications and {{ .Ops.Doubles }} squarings is derived from the
	// following addition chain generated with {{ .Meta.Module }} {{ .Meta.ReleaseTag }}.
	//
	{{- range lines (format .Script) }}
	//	{{ . }}
	{{- end }}
	//
	var z = new(Element).Set(e)
	{{- range .Program.Temporaries }}
	var {{ . }} = new(Element)
	{{- end }}
	{{ range $i := .Program.Instructions -}}
	{{- with add $i.Op }}
	{{ $i.Output }}.Mul({{ .X }}, {{ .Y }})
	{{- end -}}
	{{- with double $i.Op }}
	{{ $i.Output }}.Square({{ .X }})
	{{- end -}}
	{{- with shift $i.Op -}}
	{{- $first := 0 -}}
	{{- if ne $i.Output.Identifier .X.Identifier }}
	{{ $i.Output }}.Square({{ .X }})
	{{- $first = 1 -}}
	{{- end }}
	for s := {{ $first }}; s < {{ .S }}; s++ {
		{{ $i.Output }}.Square({{ $i.Output }})
	}
	{{- end -}}
	{{- end }}
	return e.Set(z)
}
`