commit 081f542e08cc9b04cf26119bd27fa37bec45216d
Author: mappu <mappu04@gmail.com>
Date:   Thu Oct 13 22:25:11 2016 +1300

    initial commit

diff --git a/thumbnail.go b/thumbnail.go
new file mode 100644
index 0000000..cfcd598
--- /dev/null
+++ b/thumbnail.go
@@ -0,0 +1,185 @@
+// Package thumbnail contains functions for taking the thumbnail of image and
+// video files, and caching the result for performance.
+package thumbnail
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"sync"
+	//"os/exec"
+	"strings"
+)
+
+type Thumbnailer struct {
+	Width        int
+	Height       int
+	MaxCacheSize int
+
+	cacheMtx   sync.RWMutex
+	thumbCache map[string][]byte
+}
+
+func NewThumbnailer() *Thumbnailer {
+	return &Thumbnailer{
+		Width:        100,
+		Height:       100,
+		MaxCacheSize: 10,
+		thumbCache:   make(map[string][]byte, 0),
+	}
+}
+
+func videoThumbnail(absPath string) {
+	/*
+		cmd := exec.Command(
+			"ffmpeg",
+			"-loglevel", "0",
+			"-an",
+			"-i", absPath,
+			"-vf", "thumbnail,scale=100:100",
+			"-frames:v", "1",
+			"-f", "image2pipe",
+			"-c:v", "png",
+			"-",
+		)
+	*/
+}
+
+func (this *Thumbnailer) RenderFile(absPath string) ([]byte, error) {
+	this.cacheMtx.RLock()
+	tcache, ok := this.thumbCache[absPath]
+	this.cacheMtx.RUnlock()
+
+	if ok {
+		return tcache, nil
+	}
+
+	// Add to cache
+	tcache, err := this.RenderFile_NoCache(absPath)
+	if err != nil {
+		return nil, err
+	}
+
+	this.cacheMtx.Lock()
+	// FIXME prune old cached thumbnails
+	this.thumbCache[absPath] = tcache
+	this.cacheMtx.Unlock()
+
+	return tcache, nil
+}
+
+func (this *Thumbnailer) RenderFile_NoCache(absPath string) ([]byte, error) {
+
+	fh, err := os.OpenFile(absPath, os.O_RDONLY, 0400)
+	if err != nil {
+		return nil, err
+	}
+
+	defer fh.Close()
+
+	var src image.Image
+	err = fmt.Errorf("No thumbnailer for file type")
+
+	comparePath := strings.ToLower(absPath)
+
+	if strings.HasSuffix(comparePath, "jpg") {
+		src, err = jpeg.Decode(fh)
+
+	} else if strings.HasSuffix(comparePath, "png") {
+		src, err = png.Decode(fh)
+
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return this.RenderScaledImage(src)
+}
+
+func Blend(a, b color.Color) color.Color {
+	switch a.(type) {
+	case color.RGBA:
+		return BlendRGBA(a.(color.RGBA), b.(color.RGBA)) // FIXME there's syntax for this
+
+	case color.YCbCr:
+		return BlendYCbCr(a.(color.YCbCr), b.(color.YCbCr))
+
+	default:
+		return a // ??? unknown color format
+	}
+}
+
+func BlendYCbCr(a, b color.YCbCr) color.YCbCr {
+	return color.YCbCr{
+		Y:  uint8((int(a.Y) + int(b.Y)) / 2),
+		Cb: uint8((int(a.Cb) + int(b.Cb)) / 2),
+		Cr: uint8((int(a.Cr) + int(b.Cr)) / 2),
+	}
+}
+
+func BlendRGBA(a, b color.RGBA) color.RGBA {
+	return color.RGBA{
+		R: uint8((int(a.R) + int(b.R)) / 2),
+		G: uint8((int(a.G) + int(b.G)) / 2),
+		B: uint8((int(a.B) + int(b.B)) / 2),
+		A: uint8((int(a.A) + int(b.A)) / 2),
+	}
+}
+
+func (this *Thumbnailer) RenderScaledImage(src image.Image) ([]byte, error) {
+	srcW := src.Bounds().Max.X
+	srcH := src.Bounds().Max.Y
+	destW := 0
+	destH := 0
+
+	if srcW > srcH {
+		destW = this.Width
+		destH = this.Height * srcH / srcW
+	} else {
+		destW = this.Width * srcW / srcH
+		destH = this.Height
+	}
+
+	offsetX := (this.Width - destW) / 2
+	offsetY := (this.Height - destH) / 2
+
+	scaleW := float64(srcW) / float64(destW)
+	scaleH := float64(srcH) / float64(destH)
+
+	dest := image.NewRGBA(image.Rectangle{Max: image.Point{X: this.Width, Y: this.Height}})
+
+	for y := 0; y < destH; y += 1 {
+		for x := 0; x < destW; x += 1 {
+
+			/*
+				// NN
+				mapx := int(float64(x) * scaleW)
+				mapy := int(float64(y) * scaleH)
+				dest.Set(x+offsetX, y+offsetY, src.At(mapx, mapy))
+			*/
+
+			// Bilinear
+			c00 := src.At(int(float64(x)*scaleW), int(float64(y)*scaleH))
+			c01 := src.At(int((float64(x)+0.5)*scaleW), int(float64(y)*scaleH))
+			c10 := src.At(int(float64(x)*scaleW), int((float64(y)+0.5)*scaleH))
+			c11 := src.At(int((float64(x)+0.5)*scaleW), int((float64(y)+0.5)*scaleH))
+			cBlend := Blend(Blend(c00, c01), Blend(c10, c11))
+			dest.Set(x+offsetX, y+offsetY, cBlend)
+
+		}
+	}
+
+	var b bytes.Buffer
+
+	err := png.Encode(&b, dest)
+	if err != nil {
+		return nil, err
+	}
+
+	return b.Bytes(), nil
+}