// -*- go -*-
//
// Copyright (c) 2023 Markku Rossi
//
// All rights reserved.
//

package hex

import (
	"math"
)

// Digits define the hexadecimal ASCII digits (0-9, a-f).
var Digits = []byte{
	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
	0x38, 0x39, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
}

// DecodeString decodes the bytes represented by the hexadecimal
// string s. The function returns also a boolean success value. The
// success value is false if the input string length is not even or if
// any of the runes in the input string are not valid hexadecimal
// digits (0-9, a-f, A-F).
func DecodeString(s string) ([]byte, bool) {
	result := make([]byte, len(s)/2)

	if len(s)%2 != 0 {
		return result, false
	}
	var lo, hi int32
	for i := 0; i < len(s); i += 2 {
		hi = DigitToByte(rune(s[i]))
		if hi > 0xff {
			return result, false
		}
		lo = DigitToByte(rune(s[i+1]))
		if lo > 0xff {
			return result, false
		}
		result[i/2] = hi<<4 | lo
	}
	return result, true
}

// DigitToByte converts the hexadecimal digit r to its byte value. The
// return value is math.MaxInt32 if the input digit is invalid.
func DigitToByte(r rune) int32 {
	if '0' <= r && r <= '9' {
		return r - '0'
	}
	if 'a' <= r && r <= 'f' {
		return r - 'a' + 10
	}
	if 'A' <= r && r <= 'F' {
		return r - 'A' + 10
	}
	return math.MaxInt32
}

// EncodeToString returns a hexadecimal encoding of src.
func EncodeToString(src []byte) string {
	bytes := make([]byte, len(src)*2)

	for i := 0; i < len(src); i++ {
		bytes[i*2] = Digits[src[i]>>4]
		bytes[i*2+1] = Digits[src[i]&0xf]
	}
	return string(bytes)
}

// EncodedLen returns the length of an encoding of n source
// bytes. Specifically, this returns n * 2.
func EncodedLen(n int) int {
	return n * 2
}