// Chapter 29 example: error is an interface, and your own type can satisfy it.
// Run with: go run exercises/29/06-custom-error.go

package main

import "fmt"

type levelError struct {
	level int
}

func (e levelError) Error() string {
	return fmt.Sprintf("level %d is not from 1 to 99", e.level)
}

func checkLevel(level int) error {
	if level < 1 || level > 99 {
		return levelError{level: level}
	}
	return nil
}

func main() {
	err := checkLevel(7)
	fmt.Println(err) // <nil>

	err = checkLevel(150)
	if err != nil {
		fmt.Println("Error:", err) // Error: level 150 is not from 1 to 99
	}

	// A type assertion asks for the real type inside the interface.
	bad, ok := err.(levelError)
	if ok {
		fmt.Println("The level was", bad.level) // The level was 150
	}
}