package handlers

import (
	"encoding/base64"
	"errors"
	"io"
	"net/http"
	"strings"

	"github.com/gofiber/fiber/v2"
)

const (
	maxAvatarImageBytes     = 2 << 20
	maxBackgroundImageBytes = 6 << 20
)

var (
	errImageTooLarge = errors.New("image is too large")
	errImageType     = errors.New("unsupported image type")
)

func validImageDataURI(value string) bool {
	for _, prefix := range []string{
		"data:image/png;base64,",
		"data:image/jpeg;base64,",
		"data:image/webp;base64,",
		"data:image/gif;base64,",
	} {
		if strings.HasPrefix(value, prefix) {
			return true
		}
	}
	return false
}

// readImageField accepts either a browser-resized data URI or a multipart
// upload for one image field. An empty result means the field was not changed.
func readImageField(c *fiber.Ctx, dataField, fileField string, maxBytes int64) (string, error) {
	if data := strings.TrimSpace(c.FormValue(dataField)); data != "" {
		if !validImageDataURI(data) {
			return "", errImageType
		}
		if int64(len(data)) > maxBytes*4/3+4096 {
			return "", errImageTooLarge
		}
		return data, nil
	}

	file, err := c.FormFile(fileField)
	if err != nil || file == nil || file.Size <= 0 {
		return "", nil
	}
	if file.Size > maxBytes {
		return "", errImageTooLarge
	}

	f, err := file.Open()
	if err != nil {
		return "", err
	}
	defer f.Close()

	buf, err := io.ReadAll(io.LimitReader(f, maxBytes+1))
	if err != nil {
		return "", err
	}
	if int64(len(buf)) > maxBytes {
		return "", errImageTooLarge
	}
	mime := http.DetectContentType(buf)
	if semi := strings.IndexByte(mime, ';'); semi >= 0 {
		mime = mime[:semi]
	}
	switch mime {
	case "image/png", "image/jpeg", "image/gif", "image/webp":
	default:
		return "", errImageType
	}
	return "data:" + mime + ";base64," + base64.StdEncoding.EncodeToString(buf), nil
}