package main

import (
	"fmt"
	"reflect"
)

// PrintTags prints all tag values for the given struct.
func PrintTags(s interface{}, tag string) {
	st := reflect.TypeOf(s)

	for i := 0; i < st.NumField(); i++ {
		f := st.Field(i)
		fmt.Printf("field=%s\t%s=%s\n", f.Name, tag, f.Tag.Get(tag))
	}
}

// Populate sets values of the input struct by using a struct tag as a key
// into a values map.
func Populate(s interface{}, tag string, values map[string]string) {
	st := reflect.TypeOf(s).Elem()
	v := reflect.ValueOf(s).Elem()

	for i := 0; i < st.NumField(); i++ {
		f := st.Field(i)
		key := f.Tag.Get(tag)
		value := values[key]
		v.Field(i).SetString(value)
	}
}

type Example struct {
	A string `namespace:"hello"`
	B string `namespace:"world"`
}

func main() {
	e := Example{}

	PrintTags(e, "namespace")

	values := map[string]string{
		"hello": "a",
		"world": "b",
	}
	fmt.Println(e)
	Populate(&e, "namespace", values)
	fmt.Println(e)
}