package sshmanager

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

	"golang.org/x/crypto/ssh"
)

const ServerKeyLabel = "server"

func EnsureServerKey(sshDir string) (privPath, pubPath string, pubKey string, err error) {
	if err := os.MkdirAll(sshDir, 0700); err != nil {
		return "", "", "", fmt.Errorf("creating ssh dir: %w", err)
	}

	privPath = filepath.Join(sshDir, "id_ed25519")
	pubPath = filepath.Join(sshDir, "id_ed25519.pub")

	if _, err := os.Stat(privPath); os.IsNotExist(err) {
		pub, priv, err := ed25519.GenerateKey(rand.Reader)
		if err != nil {
			return "", "", "", fmt.Errorf("generating ed25519 key: %w", err)
		}

		privFile, err := os.OpenFile(privPath, os.O_CREATE|os.O_WRONLY, 0600)
		if err != nil {
			return "", "", "", fmt.Errorf("creating private key file: %w", err)
		}
		defer privFile.Close()

		privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
		if err != nil {
			return "", "", "", fmt.Errorf("marshaling private key: %w", err)
		}
		pem.Encode(privFile, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes})

		sshPubKey, err := ssh.NewPublicKey(pub)
		if err != nil {
			return "", "", "", fmt.Errorf("wrapping public key: %w", err)
		}
		pubKey = strings.TrimSpace(string(ssh.MarshalAuthorizedKey(sshPubKey))) + " syncserver"
		if err := os.WriteFile(pubPath, []byte(pubKey), 0644); err != nil {
			return "", "", "", fmt.Errorf("writing public key: %w", err)
		}
		return privPath, pubPath, pubKey, nil
	} else if err != nil {
		return "", "", "", fmt.Errorf("checking private key: %w", err)
	}

	data, err := os.ReadFile(pubPath)
	if err != nil {
		return "", "", "", fmt.Errorf("reading public key: %w", err)
	}
	pubKey = strings.TrimSpace(string(data))
	if _, err := Fingerprint(pubKey); err != nil {
		sshPubKey, err := PublicKeyFromPrivateKeyFile(privPath)
		if err != nil {
			return "", "", "", fmt.Errorf("recovering public key: %w", err)
		}
		pubKey = sshPubKey + " syncserver"
		if err := os.WriteFile(pubPath, []byte(pubKey), 0644); err != nil {
			return "", "", "", fmt.Errorf("rewriting public key: %w", err)
		}
	}
	return privPath, pubPath, pubKey, nil
}

func ReadPrivateKey(path string) ([]byte, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	block, _ := pem.Decode(data)
	if block == nil {
		return nil, fmt.Errorf("no PEM block found")
	}
	return block.Bytes, nil
}
