From d8484bb7e0700300063792d6792d5ca7a8b3e3d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Yann=20Sala=C3=BCn?=
 <1910607+yansal@users.noreply.github.com>
Date: Thu, 10 Sep 2020 14:01:33 +0200
Subject: [PATCH] feat: add gifsicle backend (#134)

---
 engine/backend/gifsicle.go | 112 +++++++++++++++++++++++++++++++++++++
 engine/config/config.go    |  11 +++-
 engine/engine.go           |  28 +++++++---
 3 files changed, 142 insertions(+), 9 deletions(-)
 create mode 100644 engine/backend/gifsicle.go

diff --git a/engine/backend/gifsicle.go b/engine/backend/gifsicle.go
new file mode 100644
index 00000000..deccee51
--- /dev/null
+++ b/engine/backend/gifsicle.go
@@ -0,0 +1,112 @@
+package backend
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"image/gif"
+	"os/exec"
+
+	"github.com/thoas/picfit/image"
+)
+
+// Gifsicle is the gifsicle backend.
+type Gifsicle struct {
+	Path string
+}
+
+func (b *Gifsicle) String() string {
+	return "gifsicle"
+}
+
+// Fit implements Backend.
+func (b *Gifsicle) Fit(*image.ImageFile, *Options) ([]byte, error) {
+	return nil, MethodNotImplementedError
+}
+
+// Flat implements Backend.
+func (b *Gifsicle) Flat(*image.ImageFile, *Options) ([]byte, error) {
+	return nil, MethodNotImplementedError
+}
+
+// Flip implements Backend.
+func (b *Gifsicle) Flip(*image.ImageFile, *Options) ([]byte, error) {
+	return nil, MethodNotImplementedError
+}
+
+// Resize implements Backend.
+func (b *Gifsicle) Resize(imgfile *image.ImageFile, opts *Options) ([]byte, error) {
+	cmd := exec.Command(b.Path,
+		"--resize", fmt.Sprintf("%dx%d", opts.Width, opts.Height),
+	)
+	cmd.Stdin = bytes.NewReader(imgfile.Source)
+	stdout := new(bytes.Buffer)
+	cmd.Stdout = stdout
+	stderr := new(bytes.Buffer)
+	cmd.Stderr = stderr
+
+	var target *exec.ExitError
+	if err := cmd.Run(); errors.As(err, &target) && target.Exited() {
+		return nil, errors.New(stderr.String())
+	} else if err != nil {
+		return nil, err
+	}
+	return stdout.Bytes(), nil
+}
+
+// Rotate implements Backend.
+func (b *Gifsicle) Rotate(*image.ImageFile, *Options) ([]byte, error) {
+	return nil, MethodNotImplementedError
+}
+
+// Thumbnail implements Backend.
+func (b *Gifsicle) Thumbnail(imgfile *image.ImageFile, opts *Options) ([]byte, error) {
+	img, err := gif.Decode(bytes.NewReader(imgfile.Source))
+	if err != nil {
+		return nil, err
+	}
+	bounds := img.Bounds()
+	left, top, cropw, croph := computecrop(bounds.Dx(), bounds.Dy(), opts.Width, opts.Height)
+
+	cmd := exec.Command(b.Path,
+		"--crop", fmt.Sprintf("%d,%d+%dx%d", left, top, cropw, croph),
+		"--resize", fmt.Sprintf("%dx%d", opts.Width, opts.Height),
+	)
+	cmd.Stdin = bytes.NewReader(imgfile.Source)
+	stdout := new(bytes.Buffer)
+	cmd.Stdout = stdout
+	stderr := new(bytes.Buffer)
+	cmd.Stderr = stderr
+
+	var target *exec.ExitError
+	if err := cmd.Run(); errors.As(err, &target) && target.Exited() {
+		return nil, errors.New(stderr.String())
+	} else if err != nil {
+		return nil, err
+	}
+	return stdout.Bytes(), nil
+}
+
+func computecrop(srcw, srch, destw, desth int) (left, top, cropw, croph int) {
+	srcratio := float64(srcw) / float64(srch)
+	destratio := float64(destw) / float64(desth)
+
+	if srcratio > destratio {
+		cropw = int((destratio * float64(srch)) + 0.5)
+		croph = srch
+	} else {
+		croph = int((float64(srcw) / destratio) + 0.5)
+		cropw = srcw
+	}
+
+	left = int(float64(srcw-cropw) * 0.5)
+	if left < 0 {
+		left = 0
+	}
+
+	top = int(float64(srch-croph) * 0.5)
+	if top < 0 {
+		top = 0
+	}
+	return
+}
diff --git a/engine/config/config.go b/engine/config/config.go
index 349d695d..747252ad 100644
--- a/engine/config/config.go
+++ b/engine/config/config.go
@@ -1,8 +1,9 @@
 package config
 
 type Backends struct {
-	Lilliput *Backend `mapstructure:"lilliput"`
-	GoImage  *Backend `mapstructure:"goimage"`
+	Gifsicle *CommandBackend `mapstructure:"gifsicle"`
+	GoImage  *Backend        `mapstructure:"goimage"`
+	Lilliput *Backend        `mapstructure:"lilliput"`
 }
 
 type Backend struct {
@@ -10,6 +11,12 @@ type Backend struct {
 	Mimetypes []string
 }
 
+type CommandBackend struct {
+	Path      string
+	Mimetypes []string
+	Weight    int
+}
+
 // Config is the engine config
 type Config struct {
 	Backends        *Backends `mapstructure:"backends"`
diff --git a/engine/engine.go b/engine/engine.go
index 058b4938..da3b3b1a 100644
--- a/engine/engine.go
+++ b/engine/engine.go
@@ -2,6 +2,7 @@ package engine
 
 import (
 	"fmt"
+	"os/exec"
 	"sort"
 	"strings"
 
@@ -34,14 +35,20 @@ func New(cfg config.Config) *Engine {
 			mimetypes: MimeTypes,
 		})
 	} else {
-		if cfg.Backends.Lilliput != nil {
-			b = append(b, Backend{
-				Backend:   backend.NewLilliput(cfg),
-				mimetypes: cfg.Backends.Lilliput.Mimetypes,
-				weight:    cfg.Backends.Lilliput.Weight,
-			})
-		}
+		if cfg.Backends.Gifsicle != nil {
+			path := cfg.Backends.Gifsicle.Path
+			if path == "" {
+				path = "gifsicle"
+			}
 
+			if _, err := exec.LookPath(path); err == nil {
+				b = append(b, Backend{
+					Backend:   &backend.Gifsicle{Path: path},
+					mimetypes: cfg.Backends.Gifsicle.Mimetypes,
+					weight:    cfg.Backends.Gifsicle.Weight,
+				})
+			}
+		}
 		if cfg.Backends.GoImage != nil {
 			b = append(b, Backend{
 				Backend:   &backend.GoImage{},
@@ -49,6 +56,13 @@ func New(cfg config.Config) *Engine {
 				weight:    cfg.Backends.GoImage.Weight,
 			})
 		}
+		if cfg.Backends.Lilliput != nil {
+			b = append(b, Backend{
+				Backend:   backend.NewLilliput(cfg),
+				mimetypes: cfg.Backends.Lilliput.Mimetypes,
+				weight:    cfg.Backends.Lilliput.Weight,
+			})
+		}
 	}
 
 	sort.Slice(b, func(i, j int) bool {