package webutility

  
  import (
  	"net/http"
  	"encoding/json"
  )

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

  const templateHttpErr401_EN = "Unauthorized request."
  const 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) {
  	ErrorResponse(w, req, http.StatusUnauthorized, []HttpErrorDesc{

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

  	})
  }

  // TODO: Check for content type

  // WrapHandler sets common headers, checks for token validity and performs access control.
  // If authentication passes it calls the handlerFunc.

  func WrapHandler(handlerFunc http.HandlerFunc, auth bool) http.HandlerFunc {

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

  		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")
  
  		if req.Method == "OPTIONS" {
  			return
  		}

  		if auth {

  			token := req.Header.Get("Authorization")
  			if _, err := ParseAPIToken(token); err != nil {

  				UnauthorizedResponse(w, req)

  				return

  			}
  		}
  
  		err := req.ParseForm()
  		if err != nil {

  			BadRequestResponse(w, req)

  			return
  		}

  
  		// execute HandlerFunc

  		handlerFunc(w, req)

  	}
  }

  // NotFoundHandler writes HTTP error 404 to w.

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

  	ErrorResponse(w, req, http.StatusNotFound, []HttpErrorDesc{
  		{ "en", "Not found." },
  		{ "rs", "Traženi resurs ne postoji." },

  	})

  }