package nl.dedicon.pipeline.braille.calabash.impl;
   
   import com.xmlcalabash.core.XProcException;
   import com.xmlcalabash.core.XProcRuntime;
   import com.xmlcalabash.core.XProcStep;
   import com.xmlcalabash.library.DefaultStep;
   import com.xmlcalabash.runtime.XAtomicStep;
   import java.io.File;
   import java.io.IOException;
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.Arrays;
  import net.sf.saxon.s9api.QName;
  import net.sf.saxon.s9api.SaxonApiException;
  import org.apache.commons.lang3.StringUtils;
  import org.daisy.common.xproc.calabash.XProcStepProvider;
  import org.osgi.service.component.annotations.Component;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * XProc step for replacing double form feeds in BRL files
   * 
   * @author Paul Rambags
   */
  public class BrlReplaceDoubleFormFeedsStep extends DefaultStep {
  
      private static final Logger logger = LoggerFactory.getLogger(BrlReplaceDoubleFormFeedsStep.class);
  
      private static final QName _brl_uri = new QName("brl-uri");
  
      private BrlReplaceDoubleFormFeedsStep(XProcRuntime runtime, XAtomicStep step) {
          super(runtime, step);
      }
  
      @Override
      public void reset() {
      }
  
      @Override
      public void run() throws SaxonApiException {
          super.run();
  
          try {
              String brlUri = getOption(_brl_uri, "");
              if (StringUtils.isNotBlank(brlUri)) {
                  
                  try {
  
                      Path path = new File(new URI(brlUri)).toPath();
                      // The path refers to a CP850 encoded file
                      // A sequence of FF (LF)* FF is replaced by FF
                      byte[] inBytes = Files.readAllBytes(path);
                      byte[] outBytes = new byte[inBytes.length];
                      
                      int inIndex = 0;
                      int outIndex = 0;
                      while (inIndex < inBytes.length) {
                          int doubleFormFeedLength = findDoubleFormFeed(inBytes, inIndex);
                          if (doubleFormFeedLength > 0) {
                              outBytes[outIndex] = 0xC; // form feed
                              inIndex += doubleFormFeedLength;
                              outIndex ++;
                          } else {
                              outBytes[outIndex] = inBytes[inIndex];
                              inIndex ++;
                              outIndex ++;
                          }
                      }
                      
                      Files.write(path, Arrays.copyOfRange(outBytes, 0, outIndex));
  
                  } catch (URISyntaxException|IOException e) {
                      logger.error(String.format("Failed to replace double form feeds in file %s due to %s", brlUri, e.getMessage()));
                      throw e;
                  }
              }
          } catch (Exception e) {
              logger.error("dedicon:brl-replace-double-form-feeds failed", e);
              throw new XProcException(step.getNode(), e);
          }
      }
  
      // finds a C(DA)*C sequence and returns it's length
      private int findDoubleFormFeed(byte[] bytes, int index) {
          int length = 0;
          if (index + length < bytes.length && bytes[index + length] == 0xC) {
              length ++;
              while (index + length < bytes.length + 1 && bytes[index + length] == 0xD && bytes[index + length + 1] == 0xA) {
                  length += 2;
              }
              if (index + length < bytes.length && bytes[index + length] == 0xC) {
                  length ++;
                  return length;
              }
          }
          return -1;
     }
     
     @Component(
             name = "dedicon:brl-replace-double-form-feeds",
             service = {XProcStepProvider.class},
             property = {"type:String={http://www.dedicon.nl}brl-replace-double-form-feeds"}
     )
     public static class Provider implements XProcStepProvider {
 
         @Override
         public XProcStep newStep(XProcRuntime runtime, XAtomicStep step) {
             return new BrlReplaceDoubleFormFeedsStep(runtime, step);
         }
     }
 }