package nostr

import (
	"encoding/hex"
	"errors"
	"strings"

	gn "github.com/nbd-wtf/go-nostr"
	"github.com/nbd-wtf/go-nostr/nip19"
)

var (
	ErrInvalidPubkey = errors.New("invalid pubkey")
	ErrInvalidNsec   = errors.New("invalid nsec")
)

// NormalizePubkey accepts npub bech32 or 64-char hex and returns lowercase hex.
func NormalizePubkey(in string) (string, error) {
	in = strings.TrimSpace(in)
	if in == "" {
		return "", ErrInvalidPubkey
	}
	if strings.HasPrefix(in, "npub1") {
		prefix, data, err := nip19.Decode(in)
		if err != nil {
			return "", ErrInvalidPubkey
		}
		if prefix != "npub" {
			return "", ErrInvalidPubkey
		}
		s, ok := data.(string)
		if !ok {
			return "", ErrInvalidPubkey
		}
		return strings.ToLower(s), nil
	}
	if len(in) != 64 {
		return "", ErrInvalidPubkey
	}
	if _, err := hex.DecodeString(in); err != nil {
		return "", ErrInvalidPubkey
	}
	if !gn.IsValidPublicKey(in) {
		return "", ErrInvalidPubkey
	}
	return strings.ToLower(in), nil
}

// HexToNpub converts hex pubkey to npub bech32. Empty string on error.
func HexToNpub(hexpk string) string {
	npub, err := nip19.EncodePublicKey(hexpk)
	if err != nil {
		return ""
	}
	return npub
}

// NsecToHex decodes nsec1... to hex private key.
func NsecToHex(nsec string) (string, error) {
	prefix, data, err := nip19.Decode(strings.TrimSpace(nsec))
	if err != nil {
		return "", ErrInvalidNsec
	}
	if prefix != "nsec" {
		return "", ErrInvalidNsec
	}
	s, ok := data.(string)
	if !ok {
		return "", ErrInvalidNsec
	}
	return strings.ToLower(s), nil
}