package utils

// HexToCompact converts a hex path to the compact encoded format
func HexToCompact(hex []byte) []byte {
	return hexToCompact(hex)
}

func hexToCompact(hex []byte) []byte {
	terminator := byte(0)
	if hasTerm(hex) {
		terminator = 1
		hex = hex[:len(hex)-1]
	}
	buf := make([]byte, len(hex)/2+1)
	buf[0] = terminator << 5 // the flag byte
	if len(hex)&1 == 1 {
		buf[0] |= 1 << 4 // odd flag
		buf[0] |= hex[0] // first nibble is contained in the first byte
		hex = hex[1:]
	}
	decodeNibbles(hex, buf[1:])
	return buf
}

// CompactToHex converts a compact encoded path to hex format
func CompactToHex(compact []byte) []byte {
	return compactToHex(compact)
}

func compactToHex(compact []byte) []byte {
	if len(compact) == 0 {
		return compact
	}
	base := KeybytesToHex(compact)
	// delete terminator flag
	if base[0] < 2 {
		base = base[:len(base)-1]
	}
	// apply odd flag
	chop := 2 - base[0]&1
	return base[chop:]
}

func KeybytesToHex(str []byte) []byte {
	l := len(str)*2 + 1
	var nibbles = make([]byte, l)
	for i, b := range str {
		nibbles[i*2] = b / 16
		nibbles[i*2+1] = b % 16
	}
	nibbles[l-1] = 16
	return nibbles
}

func decodeNibbles(nibbles []byte, bytes []byte) {
	for bi, ni := 0, 0; ni < len(nibbles); bi, ni = bi+1, ni+2 {
		bytes[bi] = nibbles[ni]<<4 | nibbles[ni+1]
	}
}

// hasTerm returns whether a hex key has the terminator flag.
func hasTerm(s []byte) bool {
	return len(s) > 0 && s[len(s)-1] == 16
}