package utils

import (
	"crypto/md5"
	"encoding/base64"
	"fmt"
	"net/http"
	"regexp"
	"strings"
)

// ProcessBase64Image transforms a base64 encoded string from a form post and returns the MD5 hash of the data and the
// image itself as a byte slice.
func ProcessBase64Image(imageString string) (string, []byte, error) {
	if imageString == "" {
		return "", nil, fmt.Errorf("empty image string")
	}

	regex := regexp.MustCompile(`^data:.+\/(.+);base64,(.*)$`)
	matches := regex.FindStringSubmatch(imageString)
	var encodedString string
	if len(matches) > 2 {
		encodedString = regex.FindStringSubmatch(imageString)[2]
	} else {
		encodedString = imageString
	}
	imageData, err := GetDataFromBase64String(encodedString)
	if err != nil {
		return "", nil, err
	}

	return MD5FromBytes(imageData), imageData, nil
}

// GetDataFromBase64String returns the given base64 encoded string as a byte slice
func GetDataFromBase64String(encodedString string) ([]byte, error) {
	return base64.StdEncoding.DecodeString(encodedString)
}

// GetBase64StringFromData returns the given byte slice as a base64 encoded string
func GetBase64StringFromData(data []byte) string {
	return base64.StdEncoding.EncodeToString(data)

	// Really slow
	//result = regexp.MustCompile(`(.{60})`).ReplaceAllString(result, "$1\n")
	//if result[len(result)-1:] != "\n" {
	//	result += "\n"
	//}
	//return result
}

func ServeImage(image []byte, w http.ResponseWriter, r *http.Request) error {
	etag := fmt.Sprintf("%x", md5.Sum(image))

	if match := r.Header.Get("If-None-Match"); match != "" {
		if strings.Contains(match, etag) {
			w.WriteHeader(http.StatusNotModified)
			return nil
		}
	}

	contentType := http.DetectContentType(image)
	if contentType == "text/xml; charset=utf-8" || contentType == "text/plain; charset=utf-8" {
		contentType = "image/svg+xml"
	}

	w.Header().Set("Content-Type", contentType)
	w.Header().Add("Etag", etag)
	_, err := w.Write(image)
	return err
}