package relay

import (
	"encoding/hex"
	"encoding/json"
	"fmt"
	"os"
)

type keypairFile struct {
	Pub  string `json:"pub"`
	Priv string `json:"priv"`
}

// LoadOrCreateKeyPair loads an X25519 relay keypair from path, creating it if absent.
func LoadOrCreateKeyPair(path string) (*KeyPair, error) {
	data, err := os.ReadFile(path)
	if err == nil {
		var f keypairFile
		if err := json.Unmarshal(data, &f); err != nil {
			return nil, fmt.Errorf("parse relay key file: %w", err)
		}
		pubBytes, err := hex.DecodeString(f.Pub)
		if err != nil || len(pubBytes) != 32 {
			return nil, fmt.Errorf("invalid relay pub key in %s", path)
		}
		privBytes, err := hex.DecodeString(f.Priv)
		if err != nil || len(privBytes) != 32 {
			return nil, fmt.Errorf("invalid relay priv key in %s", path)
		}
		kp := &KeyPair{}
		copy(kp.Pub[:], pubBytes)
		copy(kp.Priv[:], privBytes)
		return kp, nil
	}
	if !os.IsNotExist(err) {
		return nil, fmt.Errorf("read relay key file: %w", err)
	}

	// Generate new keypair and persist.
	kp, err := GenerateKeyPair()
	if err != nil {
		return nil, err
	}
	f := keypairFile{
		Pub:  kp.PubHex(),
		Priv: hex.EncodeToString(kp.Priv[:]),
	}
	out, _ := json.MarshalIndent(f, "", "  ")
	if err := os.WriteFile(path, out, 0600); err != nil {
		return nil, fmt.Errorf("write relay key file: %w", err)
	}
	return kp, nil
}