package xraykeys

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"fmt"

	"golang.org/x/crypto/curve25519"
)

// GenerateRealityKeyPair returns Xray-compatible Reality private/public keys
// (raw URL-safe base64 without padding, same as `xray x25519`).
func GenerateRealityKeyPair() (privateKey, publicKey string, err error) {
	var priv [32]byte
	if _, err = rand.Read(priv[:]); err != nil {
		return "", "", err
	}
	priv[0] &= 248
	priv[31] &= 127
	priv[31] |= 64

	var pub [32]byte
	curve25519.ScalarBaseMult(&pub, &priv)

	privateKey = base64.RawURLEncoding.EncodeToString(priv[:])
	publicKey = base64.RawURLEncoding.EncodeToString(pub[:])
	return privateKey, publicKey, nil
}

// GenerateShortID returns a random Reality shortId (1–16 hex chars).
func GenerateShortID() (string, error) {
	b := make([]byte, 4)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return hex.EncodeToString(b), nil
}

// EnsureReality fills missing Reality keys/shortId on an inbound-like struct.
func EnsureReality(privateKey, publicKey, shortID, dest, serverNames string) (priv, pub, sid, d, names string, err error) {
	priv, pub, sid, d, names = privateKey, publicKey, shortID, dest, serverNames
	if d == "" {
		d = "www.microsoft.com:443"
	}
	if names == "" {
		names = "www.microsoft.com"
	}
	if priv == "" || pub == "" {
		priv, pub, err = GenerateRealityKeyPair()
		if err != nil {
			return "", "", "", "", "", fmt.Errorf("reality keys: %w", err)
		}
	}
	if sid == "" {
		sid, err = GenerateShortID()
		if err != nil {
			return "", "", "", "", "", fmt.Errorf("reality short id: %w", err)
		}
	}
	return priv, pub, sid, d, names, nil
}