package csgo

import (
	"encoding/binary"
	"fmt"
	"math/big"
	"regexp"
	"strings"
)

//goland:noinspection SpellCheckingInspection
var DICT = "ABCDEFGHJKLMNOPQRSTUVWXYZabcdefhijkmnopqrstuvwxyz23456789"
var sharecodeRexEx = regexp.MustCompile("^CSGO(?:-?\\w{5}){5}$")

func DecodeSharecode(code string) (uint64, uint64, uint16, error) {
	if !sharecodeRexEx.MatchString(code) {
		return 0, 0, 0, fmt.Errorf("not a CSGO sharecode: %s", code)
	}

	cleanCode := strings.ReplaceAll(strings.ReplaceAll(code, "CSGO", ""), "-", "")

	chars := ReverseString(strings.Split(cleanCode, ""))
	bigInt := new(big.Int)
	dictLenBig := big.NewInt(int64(len(DICT)))

	for _, c := range chars {
		bigInt.Mul(bigInt, dictLenBig)
		bigInt.Add(bigInt, big.NewInt(int64(strings.Index(DICT, c))))
	}

	if bigInt.BitLen() > 144 {
		return 0, 0, 0, fmt.Errorf("invalid sharecode")
	}
	bytes := make([]byte, 18)
	bigInt.FillBytes(bytes)

	matchId := binary.LittleEndian.Uint64(bytes[0:8])
	outcomeId := binary.LittleEndian.Uint64(bytes[8:16])
	tokenId := binary.LittleEndian.Uint16(bytes[16:18])

	return matchId, outcomeId, tokenId, nil
}

func ReverseString(numbers []string) []string {
	for i, j := 0, len(numbers)-1; i < j; i, j = i+1, j-1 {
		numbers[i], numbers[j] = numbers[j], numbers[i]
	}
	return numbers
}