// Chapter 21 example: the input-reading lines, in functions of their own.
// Run with: go run exercises/21/08-read-functions.go

package main

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

var reader = bufio.NewReader(os.Stdin)

// readLine prints the prompt and gives back one trimmed line. The error is
// not nil when there is no more input.
func readLine(prompt string) (string, error) {
	fmt.Print(prompt)
	text, err := reader.ReadString('\n')
	line := strings.TrimSpace(text)
	if err != nil && line == "" {
		return "", err
	}
	return line, nil
}

// readInt asks until it gets a whole number. The error is not nil when
// there is no more input.
func readInt(prompt string) (int, error) {
	for {
		line, err := readLine(prompt)
		if err != nil {
			return 0, err
		}

		number, err := strconv.Atoi(line)
		if err == nil {
			return number, nil
		}
		fmt.Println("That is not a whole number.")
	}
}

func main() {
	a, err := readInt("First number:  ")
	if err != nil {
		fmt.Println("No more input.")
		return
	}

	b, err := readInt("Second number: ")
	if err != nil {
		fmt.Println("No more input.")
		return
	}

	fmt.Printf("Sum: %d\n", a+b)
}