package main

import (
	"fmt"
	"bufio"
	"os"
	"log"
	"strconv"
)

func readInput() *string {
	reader := bufio.NewReader(os.Stdin)
	fmt.Print("Rechnung: ")
	text, err := reader.ReadString('\n')
	if err != nil {
		log.Fatal(err)
	}
	text = text[:len(text)-1]

	return &text
}

func parseCalculation(calculation *string) *int64 {
	for i := 0; i < len(*calculation); i++ { // no range because unicode would be wasteful
		if (*calculation)[i] == '+' {
			left, err := strconv.ParseInt((*calculation)[:i], 10, 64)
			if err != nil {
				log.Fatal(err)
			}
			right, err := strconv.ParseInt((*calculation)[i+1:], 10, 64)
			if err != nil {
				log.Fatal(err)
			}

			switch (*calculation)[i] {
			case '+':
				return add(&left, &right)
			default:
				log.Fatal("Unbekanntes Rechenzeichen")
			}


		}
	}
	singleNumber, err := strconv.ParseInt(*calculation, 10, 64)
	if err != nil {
		log.Fatal("Invalide Zahl")
	}

	return &singleNumber
}

func add(left *int64, right *int64) *int64 {

	result := *left + *right

	return &result
}

func main() {
	inputptr := readInput()
	resultptr := parseCalculation(inputptr)

	fmt.Printf("Ergebnis: %d", *resultptr)
}