// Package classes holds the golem15.feedback services: the screenshot
// content guard, the G15Office client and the job that files a submission
// as a G15Office task.
package classes

import (
	"bytes"
	"image"
	"net/http"

	// The decoders image.DecodeConfig needs for the allowed formats; the
	// webp decoder is registered by lagoon/attach.
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"

	_ "git.golem15.com/golem15/summercms/modules/lagoon/attach"
)

// AllowedImageMIMEs is ImageContentGuard::ALLOWED_IMAGE_MIMES.
var AllowedImageMIMEs = []string{"image/jpeg", "image/png", "image/gif", "image/webp"}

// SniffImageMIME is the finfo magic-byte sniff of ImageContentGuard: the
// content type the bytes themselves declare, independent of any file name
// or client header.
func SniffImageMIME(data []byte) string {
	return http.DetectContentType(data)
}

// IsAllowedImage ports ImageContentGuard::isAllowedImage: the bytes must
// sniff as JPEG, PNG, GIF or WebP and must decode as that image
// (getimagesize), which rejects a polyglot whose header alone looks right.
// It fails closed: empty or unreadable content is refused. The WinterCMS
// plugins keep one copy of the guard each, and so do their ports.
func IsAllowedImage(data []byte) bool {
	if len(data) == 0 {
		return false
	}
	sniffed := SniffImageMIME(data)
	allowed := false
	for _, m := range AllowedImageMIMEs {
		if sniffed == m {
			allowed = true
			break
		}
	}
	if !allowed {
		return false
	}
	cfg, format, err := image.DecodeConfig(bytes.NewReader(data))
	if err != nil || cfg.Width <= 0 || cfg.Height <= 0 {
		return false
	}
	switch format {
	case "jpeg", "png", "gif", "webp":
		return true
	}
	return false
}