From 2fcdd687f7ac52f13635689544fa471215dce753 Mon Sep 17 00:00:00 2001
From: Randall Stillwell <me@randallstillwell.com>
Date: Tue, 7 Apr 2026 13:27:16 -0500
Subject: [PATCH] Fix duplex scan rotation and swap front/back image labels
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Duplex scanners flip the sheet between sides, so odd pages (back) are
180° rotated relative to even pages (front). Landscape back pages now
rotate CCW instead of CW, and portrait back pages get a 180° flip.
Also swapped "Front"/"Back" labels to match the physical card sides.

Made-with: Cursor
---
 src/app/cards/[id]/page.tsx |  4 ++--
 src/lib/pdf.ts              | 18 ++++++++++++++----
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/app/cards/[id]/page.tsx b/src/app/cards/[id]/page.tsx
index 2fb13ea..f900b94 100644
--- a/src/app/cards/[id]/page.tsx
+++ b/src/app/cards/[id]/page.tsx
@@ -342,8 +342,8 @@ export default function CardDetailPage() {
           </CardHeader>
           <CardContent className="space-y-4">
             <div className="grid gap-4 grid-cols-1 sm:grid-cols-2">
-              <ImagePanel label="Response Card (Back)" url={card.backImageUrl as string | null} />
-              <ImagePanel label="Survey (Front)" url={card.frontImageUrl as string | null} />
+              <ImagePanel label="Response Card (Front)" url={card.backImageUrl as string | null} />
+              <ImagePanel label="Survey (Back)" url={card.frontImageUrl as string | null} />
             </div>
           </CardContent>
         </Card>
diff --git a/src/lib/pdf.ts b/src/lib/pdf.ts
index cb35da1..0334555 100644
--- a/src/lib/pdf.ts
+++ b/src/lib/pdf.ts
@@ -26,11 +26,21 @@ export async function pdfToImages(pdfBuffer: Buffer): Promise<PageImage[]> {
     if (result.buffer) {
       let buf = result.buffer as Buffer;
       let meta = await sharp(buf).metadata();
+      const w = meta.width || 0;
+      const h = meta.height || 0;
 
-      // Scanners often store landscape content with a PDF /Rotate flag that
-      // pdf2pic may not apply. Detect and rotate to portrait orientation.
-      if ((meta.width || 0) > (meta.height || 0)) {
-        buf = await sharp(buf).rotate(90).jpeg({ quality: 90 }).toBuffer();
+      // Duplex scanners flip the sheet between sides, so odd pages
+      // (back/response card) are 180° rotated relative to even pages
+      // (front/survey). Landscape pages need rotation to portrait;
+      // the direction depends on which side of the sheet was scanned.
+      const isBackSide = i % 2 === 1;
+
+      if (w > h) {
+        const angle = isBackSide ? -90 : 90;
+        buf = await sharp(buf).rotate(angle).jpeg({ quality: 90 }).toBuffer();
+        meta = await sharp(buf).metadata();
+      } else if (isBackSide) {
+        buf = await sharp(buf).rotate(180).jpeg({ quality: 90 }).toBuffer();
         meta = await sharp(buf).metadata();
       }