package portservice

import (
	"crypto/ed25519"
	"crypto/rand"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"fmt"
	"os"
	"path/filepath"

	"golang.org/x/crypto/ssh"

	"tera-clone/services/tera-api/internal/storage/atomicfile"
)

func LoadOrCreateSSHSigner(path string) (ssh.Signer, error) {
	if path == "" || !filepath.IsAbs(path) {
		return nil, errors.New("SSH host key path must be absolute")
	}
	if payload, err := os.ReadFile(path); err == nil {
		return ssh.ParsePrivateKey(payload)
	} else if !os.IsNotExist(err) {
		return nil, fmt.Errorf("read SSH host key: %w", err)
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
		return nil, fmt.Errorf("prepare SSH host key directory: %w", err)
	}
	_, privateKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return nil, fmt.Errorf("generate SSH host key: %w", err)
	}
	encoded, err := x509.MarshalPKCS8PrivateKey(privateKey)
	if err != nil {
		return nil, fmt.Errorf("encode SSH host key: %w", err)
	}
	payload := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: encoded})
	if err := atomicfile.Write(path, payload, 0o600); err != nil {
		return nil, fmt.Errorf("persist SSH host key: %w", err)
	}
	return ssh.ParsePrivateKey(payload)
}