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src/util/generateDocumentThumb.js

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+import sharp from 'sharp';
+import { spawn } from 'node:child_process';
+
+const THUMB_MAX = 200;
+
+/**
+ * Renders page 1 of a PDF into a PNG buffer using pdftocairo.
+ * @param {Buffer} pdfBuffer
+ * @returns {Promise<Buffer>}
+ */
+function renderPdfPageToPng(pdfBuffer) {
+  return new Promise((resolve, reject) => {
+    const proc = spawn('pdftocairo', ['-png', '-singlefile', '-', '-'], {
+      stdio: ['pipe', 'pipe', 'pipe'],
+    });
+
+    const chunks = [];
+    const errChunks = [];
+
+    proc.stdout.on('data', (chunk) => chunks.push(chunk));
+    proc.stderr.on('data', (chunk) => errChunks.push(chunk));
+
+    proc.on('error', (err) => {
+      reject(new Error(`Failed to start pdftocairo: ${err.message}`));
+    });
+
+    proc.on('close', (code) => {
+      if (code !== 0) {
+        const stderr = Buffer.concat(errChunks).toString('utf8').trim();
+        reject(new Error(`pdftocairo exited with code ${code}${stderr ? `: ${stderr}` : ''}`));
+      } else {
+        resolve(Buffer.concat(chunks));
+      }
+    });
+
+    proc.stdin.end(pdfBuffer);
+  });
+}
+
+/**
+ * Generates an AVIF thumbnail for a document (PDF or image).
+ * Returns { thumbavif, thumbx, thumby } or nulls if unsupported or rendering fails.
+ *
+ * @param {Buffer} content
+ * @param {string} mimetype
+ * @returns {Promise<{thumbavif: Buffer|null, thumbx: number|null, thumby: number|null}>}
+ */
+export default async function generateDocumentThumb(content, mimetype) {
+  if (!Buffer.isBuffer(content) || content.length === 0) {
+    return { thumbavif: null, thumbx: null, thumby: null };
+  }
+
+  const type = typeof mimetype === 'string' ? mimetype.trim().toLowerCase() : '';
+
+  let imageBuffer = null;
+  if (type === 'application/pdf') {
+    try {
+      imageBuffer = await renderPdfPageToPng(content);
+    } catch (err) {
+      console.warn('generateDocumentThumb: PDF render failed:', err.message);
+      return { thumbavif: null, thumbx: null, thumby: null };
+    }
+  } else if (type.startsWith('image/')) {
+    imageBuffer = content;
+  } else {
+    // Other formats (e.g. text/plain) do not have an image thumbnail
+    return { thumbavif: null, thumbx: null, thumby: null };
+  }
+
+  try {
+    const thumbResult = await sharp(imageBuffer)
+      .resize(THUMB_MAX, THUMB_MAX, { fit: 'inside', withoutEnlargement: true })
+      .avif({ effort: 4 })
+      .toBuffer({ resolveWithObject: true });
+
+    return {
+      thumbavif: thumbResult.data,
+      thumbx: thumbResult.info.width,
+      thumby: thumbResult.info.height,
+    };
+  } catch (err) {
+    console.warn('generateDocumentThumb: sharp thumbnail generation failed:', err.message);
+    return { thumbavif: null, thumbx: null, thumby: null };
+  }
+}