refactor thumbnails

Signed-off-by: Christian Richter <crichter@owncloud.com>

extensions/thumbnails/pkg/thumbnail/encoding.go

@@ -0,0 +1,112 @@
+package thumbnail
+
+import (
+	"errors"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"strings"
+)
+
+const (
+	typePng  = "png"
+	typeJpg  = "jpg"
+	typeJpeg = "jpeg"
+	typeGif  = "gif"
+)
+
+var (
+	// ErrInvalidType represents the error when a type can't be encoded.
+	ErrInvalidType = errors.New("can't encode this type")
+	// ErrNoEncoderForType represents the error when an encoder couldn't be found for a type.
+	ErrNoEncoderForType = errors.New("no encoder for this type found")
+)
+
+// Encoder encodes the thumbnail to a specific format.
+type Encoder interface {
+	// Encode encodes the image to a format.
+	Encode(io.Writer, interface{}) error
+	// Types returns the formats suffixes.
+	Types() []string
+	// MimeType returns the mimetype used by the encoder.
+	MimeType() string
+}
+
+// PngEncoder encodes to png
+type PngEncoder struct{}
+
+// Encode encodes to png format
+func (e PngEncoder) Encode(w io.Writer, img interface{}) error {
+	m, ok := img.(image.Image)
+	if !ok {
+		return ErrInvalidType
+	}
+	return png.Encode(w, m)
+}
+
+// Types returns the png suffix
+func (e PngEncoder) Types() []string {
+	return []string{typePng}
+}
+
+// MimeType returns the mimetype for png files.
+func (e PngEncoder) MimeType() string {
+	return "image/png"
+}
+
+// JpegEncoder encodes to jpg.
+type JpegEncoder struct{}
+
+// Encode encodes to jpg
+func (e JpegEncoder) Encode(w io.Writer, img interface{}) error {
+	m, ok := img.(image.Image)
+	if !ok {
+		return ErrInvalidType
+	}
+	return jpeg.Encode(w, m, nil)
+}
+
+// Types returns the jpg suffixes.
+func (e JpegEncoder) Types() []string {
+	return []string{typeJpeg, typeJpg}
+}
+
+// MimeType returns the mimetype for jpg files.
+func (e JpegEncoder) MimeType() string {
+	return "image/jpeg"
+}
+
+type GifEncoder struct{}
+
+func (e GifEncoder) Encode(w io.Writer, img interface{}) error {
+	g, ok := img.(*gif.GIF)
+	if !ok {
+		return ErrInvalidType
+	}
+	return gif.EncodeAll(w, g)
+}
+
+func (e GifEncoder) Types() []string {
+	return []string{typeGif}
+}
+
+func (e GifEncoder) MimeType() string {
+	return "image/gif"
+}
+
+// EncoderForType returns the encoder for a given file type
+// or nil if the type is not supported.
+func EncoderForType(fileType string) (Encoder, error) {
+	switch strings.ToLower(fileType) {
+	case typePng:
+		return PngEncoder{}, nil
+	case typeJpg, typeJpeg:
+		return JpegEncoder{}, nil
+	case typeGif:
+		return GifEncoder{}, nil
+	default:
+		return nil, ErrNoEncoderForType
+	}
+}