From 5b08043210b6d55681e3d98ee112ed2be36dbb17 Mon Sep 17 00:00:00 2001
From: Přemysl Eric Janouch <p@janouch.name>
Date: Thu, 28 Dec 2023 04:23:30 +0100
Subject: Teach the thumbnail command to load existing files

---
 main.go | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/main.go b/main.go
index 971391e..5dae14e 100644
--- a/main.go
+++ b/main.go
@@ -2147,7 +2147,28 @@ func cmdCheck(fs *flag.FlagSet, args []string) error {
 
 // --- Thumbnailing ------------------------------------------------------------
 
-func makeThumbnail(pathImage, pathThumb string) (int, int, error) {
+func identifyThumbnail(path string) (w, h int, err error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	config, err := webp.DecodeConfig(f)
+	if err != nil {
+		return
+	}
+	return config.Width, config.Height, nil
+}
+
+func makeThumbnail(load bool, pathImage, pathThumb string) (
+	w, h int, err error) {
+	if load {
+		if w, h, err = identifyThumbnail(pathThumb); err == nil {
+			return
+		}
+	}
+
 	thumbDirname, _ := filepath.Split(pathThumb)
 	if err := os.MkdirAll(thumbDirname, 0755); err != nil {
 		return 0, 0, err
@@ -2176,13 +2197,13 @@ func makeThumbnail(pathImage, pathThumb string) (int, int, error) {
 		return 0, 0, err
 	}
 
-	var w, h int
 	_, err = fmt.Fscanf(bytes.NewReader(out), "%d %d", &w, &h)
 	return w, h, err
 }
 
 // cmdThumbnail generates missing thumbnails, in parallel.
 func cmdThumbnail(fs *flag.FlagSet, args []string) error {
+	load := fs.Bool("load", false, "try to load existing thumbnail files")
 	if err := fs.Parse(args); err != nil {
 		return err
 	}
@@ -2215,7 +2236,7 @@ func cmdThumbnail(fs *flag.FlagSet, args []string) error {
 	return parallelize(hexSHA1, func(sha1 string) (message string, err error) {
 		pathImage := imagePath(sha1)
 		pathThumb := thumbPath(sha1)
-		w, h, err := makeThumbnail(pathImage, pathThumb)
+		w, h, err := makeThumbnail(*load, pathImage, pathThumb)
 		if err != nil {
 			if ee, ok := err.(*exec.ExitError); ok {
 				return string(ee.Stderr), nil
-- 
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