package utils

import (
	"crypto/sha1"
	"crypto/sha512"
	"encoding/base32"
	"encoding/base64"
	"golang.org/x/crypto/ed25519"
	"golang.org/x/crypto/sha3"
	"strings"
)

// GetTorHostname takes a []byte contained a DER-encoded RSA public key
// and returns the first 16 bytes of the base32 encoded sha1 hash of the key.
// This is the onion hostname of the tor service represented by the public key.
func GetTorHostname(publicKeyBytes []byte) string {
	h := sha1.New()
	h.Write(publicKeyBytes)
	sha1bytes := h.Sum(nil)

	data := base32.StdEncoding.EncodeToString(sha1bytes)
	return strings.ToLower(data[0:16])
}

// Expand ed25519.PrivateKey to (a || RH) form, return base64
func expandKey(pri ed25519.PrivateKey) string {
	h := sha512.Sum512(pri[:32])
	// Set bits so that h[:32] is private scalar "a"
	h[0] &= 248
	h[31] &= 127
	h[31] |= 64
	// Since h[32:] is RH, h is now (a || RH)
	return base64.StdEncoding.EncodeToString(h[:])
}

// V3HostnameLength is the length of a Tor V3 Onion Address (without the .onion suffix)
const V3HostnameLength = 56

// Hidden service version
const version = byte(0x03)

// Salt used to create checkdigits
const salt = ".onion checksum"

func getCheckdigits(pub ed25519.PublicKey) []byte {
	// Calculate checksum sha3(".onion checksum" || publicKey || version)
	checkstr := []byte(salt)
	checkstr = append(checkstr, pub...)
	checkstr = append(checkstr, version)
	checksum := sha3.Sum256(checkstr)
	return checksum[:2]
}

// GetTorV3Hostname converts an ed25519 public key to a valid tor onion hostname
func GetTorV3Hostname(pub ed25519.PublicKey) string {
	// Construct onion address base32(publicKey || checkdigits || version)
	checkdigits := getCheckdigits(pub)
	combined := pub[:]
	combined = append(combined, checkdigits...)
	combined = append(combined, version)
	serviceID := base32.StdEncoding.EncodeToString(combined)
	return strings.ToLower(serviceID)
}

// IsValidHostname returns true if the given address is a valid onion v3 address
func IsValidHostname(address string) bool {
	if len(address) == V3HostnameLength {
		data, err := base32.StdEncoding.DecodeString(strings.ToUpper(address))
		if err == nil {
			pubkey := data[0:ed25519.PublicKeySize]
			if GetTorV3Hostname(ed25519.PublicKey(pubkey)) == address {
				return true
			}
		}
	}
	return false
}