package relay

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"os"
	"path/filepath"
	"strings"

	"git.smesh.lol/torly/pkg/config"
	"git.smesh.lol/torly/pkg/crypto/secp256k1"
	"git.smesh.lol/torly/pkg/nostr"
)

// loadRelayKey resolves the key torly uses to sign its own events (today the
// _graph result). The key comes from TORLY_SECRET_KEY when set, otherwise from
// DATA_DIR/relay.key, which is created on first start. A relay identity must
// survive restarts, so a key file is preferred over an ephemeral key.
func loadRelayKey(cfg *config.Config) ([32]byte, error) {
	var sk [32]byte
	if raw := strings.TrimSpace(cfg.SecretKey); raw != "" {
		if err := nostr.Decode32(raw, sk[:]); err != nil {
			return sk, errors.New("secret key must be 64 lowercase hex characters")
		}
	} else {
		path := filepath.Join(cfg.DataDir, "relay.key")
		body, err := os.ReadFile(path)
		switch {
		case err == nil:
			if err := decodeKeyFile(body, sk[:]); err != nil {
				return sk, err
			}
		case os.IsNotExist(err):
			if err := createRelayKey(path, &sk); err != nil {
				return sk, err
			}
		default:
			return sk, err
		}
	}
	pub, ok := secp256k1.PubKey(sk)
	if !ok {
		return sk, errors.New("invalid relay secret key")
	}
	cfg.RelayPubKey = nostr.Hex(pub[:])
	return sk, nil
}

// decodeKeyFile accepts either the 32 raw bytes or the 64-hex text form, so a
// key generated by nak or another tool can be dropped in unchanged.
func decodeKeyFile(body, dst []byte) error {
	if len(body) == 32 {
		copy(dst, body)
		return nil
	}
	text := strings.TrimSpace(string(body))
	if err := nostr.Decode32(text, dst); err != nil {
		return errors.New("relay key file must contain 32 raw bytes or 64 hex characters")
	}
	return nil
}

func createRelayKey(path string, dst *[32]byte) error {
	for {
		if _, err := rand.Read(dst[:]); err != nil {
			return err
		}
		if _, ok := secp256k1.PubKey(*dst); ok {
			break
		}
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return err
	}
	tmp := path + ".tmp"
	text := hex.EncodeToString(dst[:]) + "\n"
	if err := os.WriteFile(tmp, []byte(text), 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, path)
}