package hws

import (
	"context"
	"io"
	"net/http"
	"net/http/httptest"

	"github.com/pkg/errors"
)

// HWSError wraps an error with other information for use with HWS features
type HWSError struct {
	StatusCode      int        // HTTP Status code
	Message         string     // Error message
	Error           error      // Error
	Level           ErrorLevel // Error level to use for logging. Defaults to Error
	RenderErrorPage bool       // If true, the servers ErrorPage will be rendered
}

type ErrorLevel string

const (
	ErrorDEBUG ErrorLevel = "Debug"
	ErrorINFO  ErrorLevel = "Info"
	ErrorWARN  ErrorLevel = "Warn"
	ErrorERROR ErrorLevel = "Error"
	ErrorFATAL ErrorLevel = "Fatal"
	ErrorPANIC ErrorLevel = "Panic"
)

// ErrorPageFunc is a function that returns an ErrorPage with the specified HTTP Status code
// This will be called by the server when it needs to render an error page
type ErrorPageFunc func(error HWSError) (ErrorPage, error)

// ErrorPage must implement a Render() function that takes in a context and ResponseWriter,
// and should write a reponse as output to the ResponseWriter.
// Server.ThrowError will call the Render() function on the current request
type ErrorPage interface {
	Render(ctx context.Context, w io.Writer) error
}

// AddErrorPage registers a handler that returns an ErrorPage
func (s *Server) AddErrorPage(pageFunc ErrorPageFunc) error {
	rr := httptest.NewRecorder()
	req := httptest.NewRequest("GET", "/", nil)
	page, err := pageFunc(HWSError{StatusCode: http.StatusInternalServerError})
	if err != nil {
		return errors.Wrap(err, "An error occured when trying to get the error page")
	}
	err = page.Render(req.Context(), rr)
	if err != nil {
		return errors.Wrap(err, "An error occured when trying to render the error page")
	}
	if len(rr.Header()) == 0 && rr.Body.String() == "" {
		return errors.New("Render method of the error page did not write anything to the response writer")
	}

	s.errorPage = pageFunc
	return nil
}

// ThrowError will write the HTTP status code to the response headers, and log
// the error with the level specified by the HWSError.
// If HWSError.RenderErrorPage is true, the error page will be rendered to the ResponseWriter
// and the request chain should be terminated.
func (s *Server) ThrowError(w http.ResponseWriter, r *http.Request, error HWSError) {
	err := s.throwError(w, r, error)
	if err != nil {
		s.LogError(error)
		s.LogError(HWSError{
			Message: "Error occured during throwError",
			Error:   errors.Wrap(err, "s.throwError"),
			Level:   ErrorERROR,
		})
	}
}

func (s *Server) throwError(w http.ResponseWriter, r *http.Request, error HWSError) error {
	if error.StatusCode <= 0 {
		return errors.New("HWSError.StatusCode cannot be 0.")
	}
	if error.Message == "" {
		return errors.New("HWSError.Message cannot be empty")
	}
	if error.Error == nil {
		return errors.New("HWSError.Error cannot be nil")
	}
	if r == nil {
		return errors.New("Request cannot be nil")
	}
	if !s.IsReady() {
		return errors.New("ThrowError called before server started")
	}
	w.WriteHeader(error.StatusCode)
	s.LogError(error)
	if s.errorPage == nil {
		s.LogError(HWSError{Message: "No error page provided", Error: nil, Level: ErrorDEBUG})
		return nil
	}
	if error.RenderErrorPage {
		s.LogError(HWSError{Message: "Error page rendering", Error: nil, Level: ErrorDEBUG})
		errPage, err := s.errorPage(error)
		if err != nil {
			s.LogError(HWSError{Message: "Failed to get a valid error page", Error: err})
		}
		err = errPage.Render(r.Context(), w)
		if err != nil {
			s.LogError(HWSError{Message: "Failed to render error page", Error: err})
		}
	} else {
		s.LogError(HWSError{Message: "Error page specified not to render", Error: nil, Level: ErrorDEBUG})
	}
	return nil
}