params.go

package main

import (
	"fmt"
	"net/http"
	"time"
)

type Params interface {
	String(r *http.Request, name string) string
}

type Binder interface {
	Bind(r *http.Request, i interface{}) error
}

type ParamsBinder struct{}

func (p ParamsBinder) Bind(r *http.Request, i interface{}) error {
	// cheating
	myParams := i.(*MyParams)

	dateStr := fmt.Sprintf(
		"%s-%s-%s",
		r.URL.Query().Get("year"),
		r.URL.Query().Get("month"),
		r.URL.Query().Get("day"),
	)

	date, err := time.Parse("2006-01-02", dateStr)
	if err != nil {
		return fmt.Errorf("invalid date %s", dateStr)
	}

	myParams.Date = date
	myParams.Name = r.URL.Query().Get("name")

	return nil
}

type QueryParams struct{}

func (q QueryParams) String(r *http.Request, name string) string {
	return r.URL.Query().Get(name)
}

type MyExtractor struct {
	Params
}

func (MyExtractor) DateFromQuery(r *http.Request) (time.Time, error) {
	dateStr := fmt.Sprintf(
		"%s-%s-%s",
		r.URL.Query().Get("year"),
		r.URL.Query().Get("month"),
		r.URL.Query().Get("day"),
	)

	date, err := time.Parse("2006-01-02", dateStr)
	if err != nil {
		return time.Time{}, fmt.Errorf("invalid date %s", dateStr)
	}

	return date, nil
}

type MyParams struct {
	Name string
	Date time.Time
}

func main() {
	req, _ := http.NewRequest("GET", "/?name=Claudemiro&year=2018&month=05&day=01", nil)
	myParams := MyParams{}

	binder := ParamsBinder{}
	if err := binder.Bind(req, &myParams); err != nil {
		panic(err)
	}

	m := MyExtractor{QueryParams{}}
	fmt.Println(m.String(req, "name"))
	fmt.Println(m.DateFromQuery(req))

	fmt.Println(myParams.Name)
	fmt.Println(myParams.Date)
}