muun-recovery/vendor/github.com/muun/libwallet/btcsuitew/btcutilw/segwit.go

package btcutilw

import (
	"bytes"
	"fmt"

	"github.com/muun/libwallet/btcsuitew/bech32m"
)

// -------------------------------------------------------------------------------------------------
// Methods below copied from btcd (address.go), but using our bech32m module instead of their bech32.
// Only that change was made. Some comments inside this code are not correct.

func encodeSegWitAddressV1(hrp string, witnessVersion byte, witnessProgram []byte) (string, error) {
	// Group the address bytes into 5 bit groups, as this is what is used to
	// encode each character in the address string.
	converted, err := bech32m.ConvertBits(witnessProgram, 8, 5, true)
	if err != nil {
		return "", err
	}

	// Concatenate the witness version and program, and encode the resulting
	// bytes using bech32 encoding.
	combined := make([]byte, len(converted)+1)
	combined[0] = witnessVersion
	copy(combined[1:], converted)
	bech, err := bech32m.Encode(hrp, combined)
	if err != nil {
		return "", err
	}

	// Check validity by decoding the created address.
	version, program, err := decodeSegWitAddressV1(bech)
	if err != nil {
		return "", fmt.Errorf("invalid taproot address: %v", err)
	}

	if version != witnessVersion || !bytes.Equal(program, witnessProgram) {
		return "", fmt.Errorf("invalid taproot address")
	}

	return bech, nil
}

func decodeSegWitAddressV1(address string) (byte, []byte, error) {
	// Decode the bech32 encoded address.
	_, data, err := bech32m.Decode(address)
	if err != nil {
		return 0, nil, err
	}

	// The first byte of the decoded address is the witness version, it must
	// exist.
	if len(data) < 1 {
		return 0, nil, fmt.Errorf("no witness version")
	}

	// ...and be <= 16.
	version := data[0]
	if version > 16 {
		return 0, nil, fmt.Errorf("invalid witness version for taproot: %v", version)
	}

	// The remaining characters of the address returned are grouped into
	// words of 5 bits. In order to restore the original witness program
	// bytes, we'll need to regroup into 8 bit words.
	regrouped, err := bech32m.ConvertBits(data[1:], 5, 8, false)
	if err != nil {
		return 0, nil, err
	}

	// The regrouped data must be between 2 and 40 bytes.
	if len(regrouped) < 2 || len(regrouped) > 40 {
		return 0, nil, fmt.Errorf("invalid data length")
	}

	// For witness version 0, address MUST be exactly 20 or 32 bytes.
	if version == 0 && len(regrouped) != 20 && len(regrouped) != 32 {
		return 0, nil, fmt.Errorf("invalid data length for witness "+
			"version 0: %v", len(regrouped))
	}

	return version, regrouped, nil
}