// Package common contains various helper functions.
package common

import (
	"encoding/hex"
	"errors"

	"github.com/ethereum/go-ethereum/common/hexutil"
)

// FromHex returns the bytes represented by the hexadecimal string s.
// s may be prefixed with "0x".
func FromHex(s string) []byte {
	if has0xPrefix(s) {
		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
}

// has0xPrefix validates str begins with '0x' or '0X'.
func has0xPrefix(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
}

// Bytes2Hex returns the hexadecimal encoding of d.
func Bytes2Hex(d []byte) string {
	return hex.EncodeToString(d)
}

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

// Hex2BytesFixed returns bytes of a specified fixed length flen.
func Hex2BytesFixed(str string, flen int) []byte {
	h, _ := hex.DecodeString(str)
	if len(h) == flen {
		return h
	}
	if len(h) > flen {
		return h[len(h)-flen:]
	}
	hh := make([]byte, flen)
	copy(hh[flen-len(h):flen], h)
	return hh
}

// ParseHexOrString tries to hexdecode b, but if the prefix is missing, it instead just returns the raw bytes
func ParseHexOrString(str string) ([]byte, error) {
	b, err := hexutil.Decode(str)
	if errors.Is(err, hexutil.ErrMissingPrefix) {
		return []byte(str), nil
	}
	return b, err
}

// 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
}

// TrimLeftZeroes returns a subslice of s without leading zeroes
func TrimLeftZeroes(s []byte) []byte {
	idx := 0
	for ; idx < len(s); idx++ {
		if s[idx] != 0 {
			break
		}
	}
	return s[idx:]
}

// TrimRightZeroes returns a subslice of s without trailing zeroes
func TrimRightZeroes(s []byte) []byte {
	idx := len(s)
	for ; idx > 0; idx-- {
		if s[idx-1] != 0 {
			break
		}
	}
	return s[:idx]
}
