package main

import (
	"errors"
	"fmt"
)

// a function that can fail, so it returns an error as the second return value
func f(arg int) (int, error) {
	if arg == 42 {
		// in case of an error, return the zero value for the result and a non-nil error
		return 0, errors.New("can't work with 42")
	}

	// simply return the result and a nil error in the success case
	return arg + 3, nil
}

// define some errors to use in makeTea
var ErrOutOfTea = fmt.Errorf("no more tea available")
var ErrPower = fmt.Errorf("can't boil water")

// a function that can fail in multiple ways, so it returns an error as the second return value
func makeTea(arg int) error {
	if arg == 2 {
		// return the error directly, so we can check for it later with errors.Is
		return ErrOutOfTea
	} else if arg == 4 {
		// use %w to wrap the error, so we can check for it later with errors.Is
		return fmt.Errorf("making tea: %w", ErrPower)
	}
	return nil
}

func main() {
	for _, i := range []int{7, 42} {

		//typical pattern for checking errors in Go: if the error is not nil, handle it and return or continue; otherwise, use the result
		if r, e := f(i); e != nil {
			fmt.Println("f failed:", e)
		} else {
			fmt.Println("f worked:", r)
		}
	}

	for i := range 5 {
		if err := makeTea(i); err != nil {

			// use errors.Is to check for specific errors, even if they are wrapped
			if errors.Is(err, ErrOutOfTea) {
				fmt.Println("We should buy new tea!")
			} else if errors.Is(err, ErrPower) { // this error is wrapped, but errors.Is can still check for it
				fmt.Println("Now it is dark.")
			} else {
				fmt.Printf("unknown error: %s\n", err)
			}
			continue
		}

		fmt.Println("Tea is ready!")
	}
}