Adrien
115 lines
4.3 KiB
Java
115 lines
4.3 KiB
Java
package com.aiteacher.document;
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import org.apache.pdfbox.Loader;
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import org.apache.pdfbox.pdmodel.PDDocument;
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import org.apache.pdfbox.pdmodel.PDPage;
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import org.apache.pdfbox.pdmodel.common.PDRectangle;
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import org.apache.pdfbox.text.PDFTextStripperByArea;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.stereotype.Service;
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import org.springframework.transaction.annotation.Transactional;
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import java.awt.Rectangle;
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import java.io.IOException;
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import java.nio.file.Path;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.UUID;
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/**
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* Parses a PDF into page-level SectionEntity records stored in Postgres.
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* Uses column-aware extraction via PDFTextStripperByArea: for two-column pages,
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* left column is extracted first then right, preserving correct reading order.
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* Text is also normalized (collapsed whitespace) before storage.
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*/
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@Service
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public class PdfStructureParser {
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private static final Logger log = LoggerFactory.getLogger(PdfStructureParser.class);
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// Right column is considered empty (single-column page) if it has < 20% of left column's content
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private static final double TWO_COLUMN_THRESHOLD = 0.2;
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private final ChapterRepository chapterRepository;
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private final SectionRepository sectionRepository;
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public PdfStructureParser(ChapterRepository chapterRepository,
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SectionRepository sectionRepository) {
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this.chapterRepository = chapterRepository;
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this.sectionRepository = sectionRepository;
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}
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@Transactional
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public List<SectionEntity> parse(UUID bookId, String bookTitle, Path pdfPath) {
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log.info("Parsing PDF structure for book {}", bookId);
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String chapterId = bookId + "-ch1";
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ChapterEntity chapter = new ChapterEntity(chapterId, bookId, 1, bookTitle, 1);
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chapterRepository.save(chapter);
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List<SectionEntity> sections = new ArrayList<>();
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try (PDDocument doc = Loader.loadPDF(pdfPath.toFile())) {
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List<PDPage> pages = new ArrayList<>();
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doc.getPages().forEach(pages::add);
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for (int i = 0; i < 25; i++) {
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int pageNum = i + 1;
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String text = normalizeWhitespace(extractPageText(pages.get(i)));
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if (text.isBlank()) continue;
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String sectionId = bookId + "-p" + pageNum;
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SectionEntity section = new SectionEntity(
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sectionId, chapterId, bookId,
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String.valueOf(pageNum),
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"Page " + pageNum,
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pageNum, pageNum,
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text
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);
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sections.add(sectionRepository.save(section));
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}
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} catch (IOException e) {
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throw new RuntimeException("Failed to parse PDF for book " + bookId, e);
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}
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log.info("Parsed {} sections for book {}", sections.size(), bookId);
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return sections;
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}
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/**
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* Extracts text from a single page using column-aware region extraction.
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* Splits the page at the horizontal midpoint. If the right region has fewer
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* than 20% of the characters of the left region, treats the page as single-column.
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*/
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private String extractPageText(PDPage page) throws IOException {
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PDRectangle mediaBox = page.getMediaBox();
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int width = (int) mediaBox.getWidth();
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int height = (int) mediaBox.getHeight();
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int mid = width / 2;
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PDFTextStripperByArea stripper = new PDFTextStripperByArea();
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stripper.setSortByPosition(true);
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stripper.addRegion("left", new Rectangle(0, 0, mid, height));
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stripper.addRegion("right", new Rectangle(mid, 0, width - mid, height));
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stripper.extractRegions(page);
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String left = stripper.getTextForRegion("left").strip();
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String right = stripper.getTextForRegion("right").strip();
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if (right.length() < left.length() * TWO_COLUMN_THRESHOLD) {
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// Single-column page — left holds all (or nearly all) content
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return left.isEmpty() ? right : left;
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}
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return left + "\n\n" + right;
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}
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/** Collapses multi-space/tab runs and excessive blank lines. */
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private String normalizeWhitespace(String text) {
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return text
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.replaceAll("[ \t]{2,}", " ")
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.replaceAll("\n{3,}", "\n\n")
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.trim();
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}
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}
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