BREAKING CHANGE(smartpdf): improve image generation quality and API consistency

- Renamed convertPDFToWebpPreviews to convertPDFToWebpBytes for consistency
- Added configurable scale options with DPI support
- Changed default scale to 3.0 (216 DPI) for better quality
- Added DPI helper methods and scale constants

test/test.ts

@@ -15,6 +15,13 @@ function ensureDir(dirPath: string): void {
   }
 }
 
+// Clean test results directory at start
+const testResultsDir = path.join('.nogit', 'testresults');
+if (fs.existsSync(testResultsDir)) {
+  fs.rmSync(testResultsDir, { recursive: true, force: true });
+}
+ensureDir(testResultsDir);
+
 tap.test('should create a valid instance of SmartPdf', async () => {
   testSmartPdf = new smartpdf.SmartPdf();
   expect(testSmartPdf).toBeInstanceOf(smartpdf.SmartPdf);
@@ -65,19 +72,108 @@ tap.test('should create PNG images from combined PDF using Puppeteer conversion'
 });
 
 tap.test('should store PNG results from both conversion functions in .nogit/testresults', async () => {
-  const testResultsDir = path.join('.nogit', 'testresults');
-  ensureDir(testResultsDir);
-
   const pdfObject = await testSmartPdf.readFileToPdfObject('.nogit/combined.pdf');
 
   // Convert using Puppeteer-based function and store images
   const imagesPuppeteer = await testSmartPdf.convertPDFToPngBytes(pdfObject.buffer);
   imagesPuppeteer.forEach((img, index) => {
-    const filePath = path.join(testResultsDir, `puppeteer_method_page_${index + 1}.png`);
+    const filePath = path.join(testResultsDir, `png_combined_page${index + 1}.png`);
     fs.writeFileSync(filePath, Buffer.from(img));
   });
 });
 
+tap.test('should create WebP preview images from PDF', async () => {
+  const pdfObject = await testSmartPdf.readFileToPdfObject('.nogit/3.pdf');
+  const webpPreviews = await testSmartPdf.convertPDFToWebpBytes(pdfObject.buffer);
+  expect(webpPreviews.length).toBeGreaterThan(0);
+  console.log('WebP preview sizes:', webpPreviews.map(img => img.length));
+  
+  // Also create PNG previews for comparison
+  const pngPreviews = await testSmartPdf.convertPDFToPngBytes(pdfObject.buffer);
+  console.log('PNG preview sizes:', pngPreviews.map(img => img.length));
+  
+  // Save the first page as both WebP and PNG preview
+  fs.writeFileSync(path.join(testResultsDir, 'webp_default_page1.webp'), Buffer.from(webpPreviews[0]));
+  fs.writeFileSync(path.join(testResultsDir, 'png_default_page1.png'), Buffer.from(pngPreviews[0]));
+});
+
+tap.test('should create WebP previews with custom scale and quality', async () => {
+  const pdfObject = await testSmartPdf.readFileToPdfObject('.nogit/3.pdf');
+  
+  // Create smaller previews with lower quality for thumbnails
+  const thumbnails = await testSmartPdf.convertPDFToWebpBytes(pdfObject.buffer, {
+    scale: 0.5,  // Create readable thumbnails at ~36 DPI
+    quality: 70
+  });
+  
+  expect(thumbnails.length).toBeGreaterThan(0);
+  console.log('Thumbnail sizes:', thumbnails.map(img => img.length));
+  
+  // Save thumbnails
+  thumbnails.forEach((thumb, index) => {
+    fs.writeFileSync(path.join(testResultsDir, `webp_thumbnail_page${index + 1}.webp`), Buffer.from(thumb));
+  });
+});
+
+tap.test('should create WebP previews with max dimensions', async () => {
+  const pdfObject = await testSmartPdf.readFileToPdfObject('.nogit/3.pdf');
+  
+  // Create previews with maximum dimensions (will use high scale but constrain to max size)
+  const constrainedPreviews = await testSmartPdf.convertPDFToWebpBytes(pdfObject.buffer, {
+    scale: smartpdf.SmartPdf.SCALE_HIGH,  // Start with high quality
+    quality: 90,
+    maxWidth: 800,
+    maxHeight: 1000
+  });
+  
+  expect(constrainedPreviews.length).toBeGreaterThan(0);
+  console.log('Constrained preview sizes:', constrainedPreviews.map(img => img.length));
+  
+  // Save constrained preview
+  fs.writeFileSync(path.join(testResultsDir, 'webp_constrained_page1.webp'), Buffer.from(constrainedPreviews[0]));
+});
+
+tap.test('should verify WebP files are smaller than PNG', async () => {
+  const pdfObject = await testSmartPdf.readFileToPdfObject('.nogit/3.pdf');
+  
+  // Generate both PNG and WebP versions at the same scale for fair comparison
+  const comparisonScale = smartpdf.SmartPdf.SCALE_HIGH; // Both use 3.0 scale
+  
+  const pngImages = await testSmartPdf.convertPDFToPngBytes(pdfObject.buffer, {
+    scale: comparisonScale
+  });
+  const webpImages = await testSmartPdf.convertPDFToWebpBytes(pdfObject.buffer, {
+    scale: comparisonScale,
+    quality: 85
+  });
+  
+  expect(pngImages.length).toEqual(webpImages.length);
+  
+  // Compare sizes
+  let totalPngSize = 0;
+  let totalWebpSize = 0;
+  
+  pngImages.forEach((png, index) => {
+    const pngSize = png.length;
+    const webpSize = webpImages[index].length;
+    totalPngSize += pngSize;
+    totalWebpSize += webpSize;
+    
+    const reduction = ((pngSize - webpSize) / pngSize * 100).toFixed(1);
+    console.log(`Page ${index + 1}: PNG=${pngSize} bytes, WebP=${webpSize} bytes, Reduction=${reduction}%`);
+    
+    // Save comparison files
+    fs.writeFileSync(path.join(testResultsDir, `comparison_png_page${index + 1}.png`), Buffer.from(png));
+    fs.writeFileSync(path.join(testResultsDir, `comparison_webp_page${index + 1}.webp`), Buffer.from(webpImages[index]));
+  });
+  
+  const totalReduction = ((totalPngSize - totalWebpSize) / totalPngSize * 100).toFixed(1);
+  console.log(`Total size reduction: ${totalReduction}% (PNG: ${totalPngSize} bytes, WebP: ${totalWebpSize} bytes)`);
+  
+  // WebP should be smaller
+  expect(totalWebpSize).toBeLessThan(totalPngSize);
+});
+
 tap.test('should close the SmartPdf instance properly', async () => {
   await testSmartPdf.stop();
 });