adds features

src/lib/pdf-thumbnails.ts

@@ -0,0 +1,71 @@
+export type PdfThumbnail = {
+	pageNumber: number;
+	imageUrl: string;
+	width: number;
+	height: number;
+};
+
+export type PdfDocumentHandle = {
+	pageCount: number;
+	thumbnails: PdfThumbnail[];
+	destroy: () => void;
+};
+
+export async function loadPdfDocument(data: Uint8Array): Promise<PdfDocumentHandle> {
+	const pdfjsLib = await import('pdfjs-dist');
+	const { getDocument, GlobalWorkerOptions } = pdfjsLib;
+
+	GlobalWorkerOptions.workerSrc = await import('pdfjs-dist/build/pdf.worker.mjs?url').then(
+		(module) => module.default
+	);
+
+	const loadingTask = getDocument({ data: new Uint8Array(data) });
+	const thumbnails: PdfThumbnail[] = [];
+
+	try {
+		const pdfDocument = await loadingTask.promise;
+
+		for (let pageNumber = 1; pageNumber <= pdfDocument.numPages; pageNumber += 1) {
+			const page = await pdfDocument.getPage(pageNumber);
+			const viewport = page.getViewport({ scale: 0.5 });
+			const canvas = document.createElement('canvas');
+			canvas.width = Math.ceil(viewport.width);
+			canvas.height = Math.ceil(viewport.height);
+			const canvasContext = canvas.getContext('2d');
+
+			if (!canvasContext) throw new Error('Could not create thumbnail canvas context.');
+
+			await page.render({ canvas, canvasContext, viewport }).promise;
+			const blob = await new Promise<Blob>((resolve, reject) => {
+				canvas.toBlob(
+					(result) =>
+						result ? resolve(result) : reject(new Error('Could not encode PDF thumbnail.')),
+					'image/png'
+				);
+			});
+
+			thumbnails.push({
+				pageNumber,
+				imageUrl: URL.createObjectURL(blob),
+				width: viewport.width,
+				height: viewport.height
+			});
+		}
+
+		let destroyed = false;
+		return {
+			pageCount: pdfDocument.numPages,
+			thumbnails,
+			destroy: () => {
+				if (destroyed) return;
+				destroyed = true;
+				for (const thumbnail of thumbnails) URL.revokeObjectURL(thumbnail.imageUrl);
+				void loadingTask.destroy();
+			}
+		};
+	} catch (error) {
+		for (const thumbnail of thumbnails) URL.revokeObjectURL(thumbnail.imageUrl);
+		await loadingTask.destroy();
+		throw error;
+	}
+}