package main

import (
	"fmt"
	"os"
	"time"
	"github.com/pkg/errors"
	"strings"
)

// 1. use interfaces to interact between modules

type Person interface {
	GetName() string
	GetAge() int
}

// implementation
type Man struct {
	name string
	age  int
}

func (m Man) GetName() string {
	return m.name
}

func (m Man) GetAge() int {
	return m.age
}

func printPerson(person Person) {
	fmt.Printf("Name %s. Age %d", person.GetName(), person.GetAge())
}

// 2. Do not ignore errors

func test() error {
	// Good
	if err := os.Chown("/tmp/test", 2, 2); err != nil {
		return err
	}
	return nil
	// Bad
	// os.Chown("/tmp/test", 2, 2)
}

// 3. letter case struct fields are not available from other modules struct functions and cat not be serializable via Json

func test1() {
	p := Man{}

	// Not available from foreign modules
	// p.name

	// Use methods instead
	// p.GetName()

	// Or fields starting with Upper case(BAD)
	// p.Name

	// Create special structure with upper case fields for marshalling and unmarshalling

	fmt.Printf("Data: %v", p)
}

// 4. for cycle

func main1() {
	g := []int{1, 2, 3, 4, 5, 6, 7}

	// Bad
	for _, value := range g {
		go func() {
			fmt.Printf("Value is: %d \n", value)
		}()
	}
	time.Sleep(time.Duration(2) * time.Second)

	// Good
	for _, value := range g {
		// pass cycle value as function parameter!
		go func(param int) {
			fmt.Printf("Value is: %d \n", param)
		}(value)
	}
	time.Sleep(time.Duration(2) * time.Second)
}

// 5. if clause
func test51() (string, error) {
	return "lol", nil
}

func main() {
	var res string

	// pay attention to so-called variables inside if-clause
	if res, _ := test51(); res != "" {
		// res variable scope
		fmt.Printf("Res: %s \n", res)
	}

	fmt.Printf("Res: %s \n", res)

	// do not allow golang to make decision about partially definition
	res, err := test51()
	_ = err

	// res variable scope
	fmt.Printf("Res: %s \n", res)
}

// 6. errors are not strings

func test6() {
	err1 := errors.New("test error")
	err2 := errors.New("test1 error")

	if err1 == err2 {
		fmt.Printf("wtf?")
	}

	fmt.Printf("Err1: %s. Err2: %s", err1, err2)

	// please, no
	if strings.Contains(err1.Error(), "test ") {

	}

	// more advanced error handling - later
}

// Course: Effective go
// https://talks.golang.org/2012/10things.slide#1