start refactor of media package

internal/media/processing.go

@@ -0,0 +1,190 @@
+package media
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+
+	"github.com/buckket/go-blurhash"
+	"github.com/nfnt/resize"
+	"github.com/superseriousbusiness/exifremove/pkg/exifremove"
+)
+
+// purgeExif is a little wrapper for the action of removing exif data from an image.
+// Only pass pngs or jpegs to this function.
+func purgeExif(data []byte) ([]byte, error) {
+	if len(data) == 0 {
+		return nil, errors.New("passed image was not valid")
+	}
+
+	clean, err := exifremove.Remove(data)
+	if err != nil {
+		return nil, fmt.Errorf("could not purge exif from image: %s", err)
+	}
+
+	if len(clean) == 0 {
+		return nil, errors.New("purged image was not valid")
+	}
+	
+	return clean, nil
+}
+
+func deriveGif(b []byte, extension string) (*imageAndMeta, error) {
+	var g *gif.GIF
+	var err error
+	switch extension {
+	case mimeGif:
+		g, err = gif.DecodeAll(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("extension %s not recognised", extension)
+	}
+
+	// use the first frame to get the static characteristics
+	width := g.Config.Width
+	height := g.Config.Height
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	return &imageAndMeta{
+		image:  b,
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+func deriveImage(b []byte, contentType string) (*imageAndMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImageJpeg:
+		i, err = jpeg.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case mimeImagePng:
+		i, err = png.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("content type %s not recognised", contentType)
+	}
+
+	width := i.Bounds().Size().X
+	height := i.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	return &imageAndMeta{
+		image:  b,
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+// deriveThumbnail returns a byte slice and metadata for a thumbnail of width x and height y,
+// of a given jpeg, png, or gif, or an error if something goes wrong.
+//
+// Note that the aspect ratio of the image will be retained,
+// so it will not necessarily be a square, even if x and y are set as the same value.
+func deriveThumbnail(b []byte, contentType string, x uint, y uint) (*imageAndMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImageJpeg:
+		i, err = jpeg.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case mimeImagePng:
+		i, err = png.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case mimeImageGif:
+		i, err = gif.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("content type %s not recognised", contentType)
+	}
+
+	thumb := resize.Thumbnail(x, y, i, resize.NearestNeighbor)
+	width := thumb.Bounds().Size().X
+	height := thumb.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	tiny := resize.Thumbnail(32, 32, thumb, resize.NearestNeighbor)
+	bh, err := blurhash.Encode(4, 3, tiny)
+	if err != nil {
+		return nil, err
+	}
+
+	out := &bytes.Buffer{}
+	if err := jpeg.Encode(out, thumb, &jpeg.Options{
+		Quality: 75,
+	}); err != nil {
+		return nil, err
+	}
+	return &imageAndMeta{
+		image:    out.Bytes(),
+		width:    width,
+		height:   height,
+		size:     size,
+		aspect:   aspect,
+		blurhash: bh,
+	}, nil
+}
+
+// deriveStaticEmojji takes a given gif or png of an emoji, decodes it, and re-encodes it as a static png.
+func deriveStaticEmoji(b []byte, contentType string) (*imageAndMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImagePng:
+		i, err = png.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case mimeImageGif:
+		i, err = gif.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("content type %s not allowed for emoji", contentType)
+	}
+
+	out := &bytes.Buffer{}
+	if err := png.Encode(out, i); err != nil {
+		return nil, err
+	}
+	return &imageAndMeta{
+		image: out.Bytes(),
+	}, nil
+}
+
+type imageAndMeta struct {
+	image    []byte
+	width    int
+	height   int
+	size     int
+	aspect   float64
+	blurhash string
+}