package webutility

  
  import (

  	"encoding/json"

  	"net/http"

  )

  const (
  	templateHttpErr500_EN = "An internal server error has occurred."
  	templateHttpErr500_RS = "Došlo je do greške na serveru."
  	templateHttpErr400_EN = "Bad request: invalid request body."
  	templateHttpErr400_RS = "Neispravan zahtev."
  	templateHttpErr401_EN = "Unauthorized request."
  	templateHttpErr401_RS = "Neautorizovan zahtev."
  )

  type httpError struct {

  	Error   []HttpErrorDesc `json:"error"`
  	Request string          `json:"request"`
  }
  
  type HttpErrorDesc struct {
  	Lang string `json:"lang"`
  	Desc string `json:"description"`
  }

  // ErrorResponse writes HTTP error to w.

  func ErrorResponse(w http.ResponseWriter, r *http.Request, code int, desc []HttpErrorDesc) {

  	err := httpError{desc, r.Method + " " + r.URL.Path}

  	w.WriteHeader(code)
  	json.NewEncoder(w).Encode(err)
  }

  // BadRequestResponse writes HTTP error 400 to w.

  func BadRequestResponse(w http.ResponseWriter, req *http.Request) {
  	ErrorResponse(w, req, http.StatusBadRequest, []HttpErrorDesc{

  		{"en", templateHttpErr400_EN},
  		{"rs", templateHttpErr400_RS},

  	})

  }

  // InternalSeverErrorResponse writes HTTP error 500 to w.

  func InternalServerErrorResponse(w http.ResponseWriter, req *http.Request) {
  	ErrorResponse(w, req, http.StatusInternalServerError, []HttpErrorDesc{

  		{"en", templateHttpErr500_EN},
  		{"rs", templateHttpErr500_RS},

  	})

  }

  // UnauthorizedError writes HTTP error 401 to w.

  func UnauthorizedResponse(w http.ResponseWriter, req *http.Request) {

  	w.Header().Set("WWW-Authenticate", "Bearer")

  	ErrorResponse(w, req, http.StatusUnauthorized, []HttpErrorDesc{

  		{"en", templateHttpErr401_EN},
  		{"rs", templateHttpErr401_RS},

  	})
  }

  // NotFoundHandler writes HTTP error 404 to w.

  func NotFoundHandler(w http.ResponseWriter, req *http.Request) {

  	SetDefaultHeaders(w)
  	if req.Method == "OPTIONS" {
  		return
  	}

  	ErrorResponse(w, req, http.StatusNotFound, []HttpErrorDesc{

  		{"en", "Not found."},
  		{"rs", "Traženi resurs ne postoji."},

  	})

  }

  // SetDefaultHeaders set's default headers for an HTTP response.

  func SetDefaultHeaders(w http.ResponseWriter) {
  	w.Header().Set("Access-Control-Allow-Origin", "*")

  	w.Header().Set("Access-Control-Allow-Methods", "POST, GET, PUT, DELETE, OPTIONS")

  	w.Header().Set("Access-Control-Allow-Headers", `Accept, Content-Type,
  		Content-Length, Accept-Encoding, X-CSRF-Token, Authorization`)

  	w.Header().Set("Content-Type", "application/json; charset=utf-8")
  }