package utils

import "encoding/hex"

// use to look up number of 1 bit in 4 bits
var halfByteLookup = [16]int{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4}

// FromHex returns the bytes represented by the hexadecimal string s.
// s may be prefixed with "0x".
func FromHex(s string) []byte {
	if len(s) > 1 {
		if s[0:2] == "0x" || s[0:2] == "0X" {
			s = s[2:]
		}
	}
	if len(s)%2 == 1 {
		s = "0" + s
	}
	return Hex2Bytes(s)
}

// CopyBytes returns an exact copy of the provided bytes.
func CopyBytes(b []byte) (copiedBytes []byte) {
	if b == nil {
		return nil
	}
	copiedBytes = make([]byte, len(b))
	copy(copiedBytes, b)

	return
}

// HasHexPrefix validates str begins with '0x' or '0X'.
func HasHexPrefix(str string) bool {
	return len(str) >= 2 && str[0] == '0' && (str[1] == 'x' || str[1] == 'X')
}

// isHexCharacter returns bool of c being a valid hexadecimal.
func isHexCharacter(c byte) bool {
	return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') || ('A' <= c && c <= 'F')
}

// IsHex validates whether each byte is valid hexadecimal string.
func IsHex(str string) bool {
	if len(str)%2 != 0 {
		return false
	}
	for _, c := range []byte(str) {
		if !isHexCharacter(c) {
			return false
		}
	}
	return true
}

// Hex2Bytes returns the bytes represented by the hexadecimal string str.
func Hex2Bytes(str string) []byte {
	h, _ := hex.DecodeString(str)
	return h
}

// RightPadBytes zero-pads slice to the right up to length l.
func RightPadBytes(slice []byte, l int) []byte {
	if l <= len(slice) {
		return slice
	}

	padded := make([]byte, l)
	copy(padded, slice)

	return padded
}

// LeftPadBytes zero-pads slice to the left up to length l.
func LeftPadBytes(slice []byte, l int) []byte {
	if l <= len(slice) {
		return slice
	}

	padded := make([]byte, l)
	copy(padded[l-len(slice):], slice)

	return padded
}

// counts number of one bits in a byte
func countOneBitsInByte(by byte) int {
	return halfByteLookup[by&0x0F] + halfByteLookup[by>>4]
}

// CountOneBits counts the number of 1 bit in byte array
func CountOneBits(arr []byte) int {
	count := 0
	for i := range arr {
		count += countOneBitsInByte(arr[i])
	}
	return count
}