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EPUBCheck is a tool to validate the conformance of EPUB publications against the EPUB specifications. EPUBCheck can be run as a standalone command-line tool or used as a Java library.

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package org.idpf.epubcheck.util.saxon;

import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.lib.ExtensionFunctionCall;
import net.sf.saxon.lib.ExtensionFunctionDefinition;
import net.sf.saxon.om.NodeInfo;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.om.StructuredQName;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.Int64Value;
import net.sf.saxon.value.SequenceType;

public class ColumnNumberFunction extends ExtensionFunctionDefinition
{

  public static StructuredQName QNAME = new StructuredQName("saxon", "http://saxon.sf.net/", "column-number");

  @Override
  public StructuredQName getFunctionQName()
  {
    return QNAME;
  }

  @Override
  public int getMaximumNumberOfArguments()
  {
    return 1;
  }

  @Override
  public int getMinimumNumberOfArguments()
  {
    return 0;
  }

  @Override
  public SequenceType[] getArgumentTypes()
  {
    return new SequenceType[]{SequenceType.SINGLE_NODE};
  }

  @Override
  public SequenceType getResultType(SequenceType[] suppliedArgumentTypes)
  {
    return SequenceType.SINGLE_INTEGER;
  }

  @Override
  public boolean dependsOnFocus()
  {
    return true;
  }

  @Override
  public boolean trustResultType()
  {
    return true;
  }

  @Override
  public ExtensionFunctionCall makeCallExpression()
  {
    return new ExtensionFunctionCall()
    {
      public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException
      {
        if (context.getContextItem() instanceof NodeInfo)
        {
          return new Int64ValueSequence(new Int64Value(((NodeInfo) context.getContextItem()).getColumnNumber()));
        }
        throw new XPathException("Unexpected XPath context for saxon:column-number");
      }
    };
  }
}