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Java Library to call Mindee's Off-The-Shelf and Custom APIs
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package com.mindee.input;

import com.mindee.MindeeException;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.text.PDFTextStripper;

/**
 * Utilities for working with files.
 */
public class InputSourceUtils {

  private InputSourceUtils() {
  }

  private static final String WINDOWS_FILE_SEPARATOR = "\\";
  private static final String UNIX_FILE_SEPARATOR = "/";
  private static final String FILE_EXTENSION = ".";

  /**
   * Returns the file's extension.
   */
  public static String getFileExtension(String fileName) {
    if (fileName == null) {
      throw new IllegalArgumentException("fileName must not be null!");
    }

    String extension = "";

    int indexOfLastExtension = fileName.lastIndexOf(FILE_EXTENSION);

    // check last file separator, windows and unix
    int lastSeparatorPosWindows = fileName.lastIndexOf(WINDOWS_FILE_SEPARATOR);
    int lastSeparatorPosUnix = fileName.lastIndexOf(UNIX_FILE_SEPARATOR);

    // takes the greater of the two values, which means last file separator
    int indexOflastSeparator = Math.max(lastSeparatorPosWindows, lastSeparatorPosUnix);

    // make sure the file extension appears after the last file separator
    if (indexOfLastExtension > indexOflastSeparator) {
      extension = fileName.substring(indexOfLastExtension + 1);
    }

    return extension;
  }

  /**
   * Split the filename into a name and an extension.
   *
   * @param filename the filename to split.
   * @return first element is name, second is extension.
   */
  public static String[] splitNameStrict(String filename) throws MindeeException {
    String name;
    String extension;
    int index = filename.lastIndexOf(FILE_EXTENSION);
    if (index > 0) {
      extension = filename.substring(index + 1);
      name = filename.substring(0, index);
    } else {
      throw new MindeeException("File name must include a valid extension.");
    }
    return new String[] {name, extension};
  }

  /**
   * Returns true if the file is a PDF.
   */
  public static boolean isPdf(byte[] fileBytes) {
    try (PDDocument document = PDDocument.load(new ByteArrayInputStream(fileBytes))) {
      return true;
    } catch (IOException e) {
      return false;
    }
  }

  /**
   * Ensures the URL can be sent to the Mindee server.
   */
  public static void validateUrl(URL inputUrl) {
    if (!"https".equalsIgnoreCase(inputUrl.getProtocol())) {
      throw new MindeeException("Only HTTPS source URLs are allowed");
    }
  }

  /**
   * Returns true if the source PDF has source text inside. Returns false for images.
   *
   * @param fileBytes A byte array representing a PDF.
   * @return True if at least one character exists in one page.
   * @throws MindeeException if the file could not be read.
   */
  public static boolean hasSourceText(byte[] fileBytes) {
    try {
      PDDocument document = PDDocument.load(new ByteArrayInputStream(fileBytes));
      PDFTextStripper stripper = new PDFTextStripper();

      for (int i = 0; i < document.getNumberOfPages(); i++) {
        stripper.setStartPage(i + 1);
        stripper.setEndPage(i + 1);
        String pageText = stripper.getText(document);
        if (!pageText.trim().isEmpty()) {
          document.close();
          return true;
        }
      }
      document.close();
    } catch (IOException e) {
      return false;
    }

    return false;
  }
}