package main

import (
  "os"
  "crypto/ed25519"
  "crypto/rand"
  "crypto/x509"
  "encoding/pem"
  "fmt"
)

func usage(code int, err error) {
  if err != nil {
    fmt.Fprintf(os.Stderr, "error: %s\n", err)
  }
  fmt.Fprintf(os.Stderr, "usage: %s [output_path]\n", os.Args[0])
  os.Exit(code)
}

func main() {
  if len(os.Args) != 2 {
    usage(0, nil)
  }
  output_path := os.Args[1]

  private_file, err := os.Create(output_path)
  if err != nil {
    usage(1, err)
  }

  public_file, err := os.Create(fmt.Sprintf("%s.pub", output_path))
  if err != nil {
    usage(2, err)
  }

  public, private, err := ed25519.GenerateKey(rand.Reader)
  if err != nil {
    usage(3, err)
  }

  public_bytes, err := x509.MarshalPKIXPublicKey(public)
  if err != nil {
    usage(4, err)
  }

  private_bytes, err := x509.MarshalPKCS8PrivateKey(private)
  if err != nil {
    usage(5, err)
  }

  err = pem.Encode(public_file, &pem.Block{
    Type: "PUBLIC KEY",
    Bytes: public_bytes,
  })

  err = pem.Encode(private_file, &pem.Block{
    Type: "PRIVATE KEY",
    Bytes: private_bytes,
  })
  err = public_file.Close()
  if err != nil {
    usage(6, err)
  }

  err = private_file.Close()
  if err != nil {
    usage(7, err)
  }
  fmt.Printf("Wrote %s and %s.pub\n", output_path, output_path)
}