watch-only.scala

import scala.util.Success
import org.bitcoins.core.protocol.script._
import org.bitcoins.core.protocol.Bech32Address
import org.bitcoins.core.config.TestNet3

//                          first account -------┐
//                          bitcoin ----------┐  |
//                          segwit --------┐  |  |
val accountPath = BIP32Path.fromString("m/84'/0'/0'")
// accountPath: BIP32Path = m/84'/0'/0'
val accountXpub = {
    // this key is sensitive, keep away from prying eyes!
    val accountXpriv = xpriv.deriveChildPrivKey(accountPath)

    // this key is not sufficient to spend from, but we
    // can generate addresses with it!
    accountXpriv.extPublicKey
}
// accountXpub: ExtPublicKey = zpub6rFVjPLJN2jSekPmRnBZAuLXy9K82puEBdHnf7Dt9LutwRhBjHRn9iZXwJijfbcpwugM5FNQe2pHfBcXjefbf6KSj7ueP9e3qL32JVyexKr

                              // address no. 0 ---------------┐
                              // external address ----------┐ |
val firstAddressPath = SegWitHDPath.fromString("m/84'/0'/0'/0/0")
// firstAddressPath: SegWitHDPath = m/84'/0'/0'/0/0
val firstAccountAddress = {
    // this is a bit quirky, but we're not interesting in
    // deriving the complete path from our account xpub
    // instead, we're only interested in the part after
    // the account level (3rd level). the .diff() method
    // achieves that
    val Some(pathDiff) = accountPath.diff(firstAddressPath)

    // deriving public keys from hardened extended keys
    // is not possible, that's why .deriveChildPubKey()
    // returns a Try[ExtPublicKey]. A hardened key is marked
    // by a ' after the number in the notation we use above.
    val Success(extPubKey) = accountXpub.deriveChildPubKey(pathDiff)
    val pubkey = extPubKey.key
    val scriptPubKey = P2WPKHWitnessSPKV0(pubkey)
    Bech32Address(scriptPubKey, TestNet3)
}
// firstAccountAddress: Bech32Address = Bech32Address(tb1qdymd8a5z85d6nrafn3p7few8z7pk5spd4qejmx)

// tada! We just generated an address you can send money to,
// without having access to the private key!
firstAccountAddress.value
// res2: String = tb1qdymd8a5z85d6nrafn3p7few8z7pk5spd4qejmx

// you can now continue deriving addresses from the same public
// key, by imitating what we did above. To get the next
// HD path to generate an address at:
val nextAddressPath: SegWitHDPath = firstAddressPath.next
// nextAddressPath: SegWitHDPath = m/84'/0'/0'/0/1