OCR: extract util functions

src/common/util/ocrUtils.ts

@@ -0,0 +1,100 @@
+/**
+ * Shared OCR utilities using Tesseract.js
+ *
+ * Used by:
+ * - image-ocr converter (single image)
+ * - pdf-auto converter (multi-page fallback)
+ * - pdf-images-ocr converter (forced OCR on PDF pages)
+ */
+
+
+/**
+ * Result of OCR operation with quality metadata
+ */
+export interface OcrResult {
+  text: string;
+  avgCharsPerPage: number;
+  pageCount: number;
+}
+
+
+/**
+ * OCR a single image with progress tracking
+ *
+ * @param imageData - Blob or base64 data URL
+ * @param onProgress - Progress callback (0-1)
+ * @returns Extracted text
+ */
+export async function ocrImageWithProgress(
+  imageData: Blob | string,
+  onProgress?: (progress: number) => void,
+): Promise<string> {
+  const { recognize } = await import('tesseract.js');
+  let lastProgress = -1;
+
+  const { data: page } = await recognize(imageData, undefined, {
+    errorHandler: e => {
+      // NOTE: shall we inform the user about the error?
+      console.error('[OCR Error]', e);
+    },
+    logger: (message) => {
+      if (!onProgress || message.status !== 'recognizing text')
+        return;
+      if (message.progress > lastProgress + 0.01) {
+        lastProgress = message.progress;
+        onProgress(message.progress);
+      }
+    },
+  });
+
+  return page.text;
+}
+
+
+/**
+ * OCR multiple PDF page images with cumulative progress tracking
+ *
+ * @param imageDataURLs - Array of rendered PDF page images
+ * @param onProgress - Progress callback (0-1, cumulative across all pages)
+ * @returns Combined text from all pages with quality metadata
+ */
+export async function ocrPdfPagesWithProgress(
+  imageDataURLs: Array<{ mimeType: string; base64Data: string }>,
+  onProgress?: (progress: number) => void,
+): Promise<OcrResult> {
+
+  const pageTexts: string[] = [];
+  const totalPages = imageDataURLs.length;
+
+  for (let pageNum = 0; pageNum < totalPages; pageNum++) {
+    const pageImage = imageDataURLs[pageNum];
+
+    // Convert base64 to data URL for Tesseract
+    const dataUrl = `data:${pageImage.mimeType};base64,${pageImage.base64Data}`;
+    const pageText = await ocrImageWithProgress(dataUrl,
+      (pageProgress) => {
+        // Distribute progress across all pages
+        const cumulativeProgress = (pageNum + pageProgress) / totalPages;
+        onProgress?.(cumulativeProgress);
+      },
+    );
+
+    pageTexts.push(pageText);
+
+    // Update progress after each page completes
+    onProgress?.((pageNum + 1) / totalPages);
+  }
+
+  // Combine pages with informative separators for multi-page PDFs
+  const combinedText = pageTexts
+    .map((text, i) => `--- Page ${i + 1}/${totalPages} (OCR) ---\n\n${text}`)
+    .join('\n\n') + `\n\n--- End of OCR Document | If content is missing or garbled, re-attach PDF as images ---`;
+
+  const trimmedLength = combinedText.trim().length;
+
+  return {
+    text: combinedText,
+    pageCount: totalPages,
+    avgCharsPerPage: totalPages > 0 ? trimmedLength / totalPages : 0,
+  };
+}