From 599568382e3de09eb68ec4be200ef2b26fdba6af Mon Sep 17 00:00:00 2001
From: Laura <milanbartky@gmail.com>
Date: Thu, 19 Jun 2025 12:50:31 +0200
Subject: [PATCH] gif

---
 internal/codec/gif/gif.go | 72 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 internal/codec/gif/gif.go

diff --git a/internal/codec/gif/gif.go b/internal/codec/gif/gif.go
new file mode 100644
index 0000000..be9d52b
--- /dev/null
+++ b/internal/codec/gif/gif.go
@@ -0,0 +1,72 @@
+package gif
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/gif"
+	"io"
+
+	"github.com/coalaura/ffwebp/internal/codec"
+	"github.com/coalaura/ffwebp/internal/opts"
+	"github.com/urfave/cli/v3"
+)
+
+var numColors int
+
+func init() {
+	codec.Register(impl{})
+}
+
+type impl struct{}
+
+func (impl) Name() string {
+	return "gif"
+}
+
+func (impl) Extensions() []string {
+	return []string{"gif"}
+}
+
+func (impl) Flags(flags []cli.Flag) []cli.Flag {
+	return append(flags, &cli.IntFlag{
+		Name:        "gif.colors",
+		Usage:       "GIF: Number of colors (1-256)",
+		Value:       256,
+		Destination: &numColors,
+		Validator: func(value int) error {
+			if value < 1 || value > 256 {
+				return fmt.Errorf("invalid number of colors: %d", value)
+			}
+
+			return nil
+		},
+	})
+}
+
+func (impl) Sniff(reader io.ReaderAt) (int, error) {
+	magic7a := []byte("GIF87a")
+	magic9a := []byte("GIF89a")
+
+	buf := make([]byte, 6)
+
+	if _, err := reader.ReadAt(buf, 0); err != nil {
+		return 0, err
+	}
+
+	if bytes.Equal(buf, magic7a) || bytes.Equal(buf, magic9a) {
+		return 100, nil
+	}
+
+	return 0, nil
+}
+
+func (impl) Decode(reader io.Reader) (image.Image, error) {
+	return gif.Decode(reader)
+}
+
+func (impl) Encode(writer io.Writer, img image.Image, options opts.Common) error {
+	return gif.Encode(writer, img, &gif.Options{
+		NumColors: numColors,
+	})
+}