package web

import (
	"errors"
	"fmt"
	"mime/multipart"
	"net/http"
	"path"
	"strings"
)

// parseUpload parses a multipart form with a file in the "file" field. On
// failure it returns an HTTP status and a message for the page.
//
// Files bigger than 1 MB are spooled to temporary files rather than kept in
// memory; net/http removes them when the handler returns.
func (s *Server) parseUpload(w http.ResponseWriter, r *http.Request) (multipart.File, *multipart.FileHeader, int, string) {
	// Allow some slack over the file size limit for the multipart framing and form fields.
	r.Body = http.MaxBytesReader(w, r.Body, s.cfg.MaxUploadBytes+64<<10)
	if err := r.ParseMultipartForm(1 << 20); err != nil {
		var tooBig *http.MaxBytesError
		if errors.As(err, &tooBig) {
			return nil, nil, http.StatusRequestEntityTooLarge, "file too large; the maximum upload is " + s.maxUpload()
		}
		return nil, nil, http.StatusBadRequest, "bad upload: " + err.Error()
	}
	file, hdr, err := r.FormFile("file")
	if err != nil {
		return nil, nil, http.StatusBadRequest, "choose a pcap file"
	}
	return file, hdr, 0, ""
}

func (s *Server) maxUpload() string {
	return fmt.Sprintf("%d MB", s.cfg.MaxUploadBytes/1e6)
}

// uploadStem returns the sanitized name of an uploaded file without its extension.
func uploadStem(hdr *multipart.FileHeader) string {
	name := safeName(hdr.Filename, "capture.pcap")
	return strings.TrimSuffix(name, path.Ext(name))
}