public class SetHeaderExtensionFunction extends ExtensionFunctionDefinition {

    private static final long serialVersionUID = 1L;

    @Override
    public StructuredQName getFunctionQName() {
        return new StructuredQName("", "http://sap.com/it/", "setHeader");
    }

    @Override
    public int getMinimumNumberOfArguments() {
        return 3;
    }

    @Override
    public int getMaximumNumberOfArguments() {
        return 3;
    }

    @Override
    public SequenceType[] getArgumentTypes() {
        return new SequenceType[] { SequenceType.SINGLE_ITEM, SequenceType.SINGLE_STRING, SequenceType.SINGLE_ITEM };
    }

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

    @Override
    public ExtensionFunctionCall makeCallExpression() {
        return new ExtensionFunctionCall() {
            private static final long serialVersionUID = 1L;

            @Override
            public Sequence call(XPathContext xPathContext, Sequence[] arguments) throws XPathException {
                // 1st argument (mandatory, index 0)
                ObjectValue arg1 = (ObjectValue) arguments[0].iterate().next();
                Exchange exchange;
                if (arg1.getObject() instanceof Exchange) {
                    exchange = (Exchange) arg1.getObject();
                } else {
                    throw new XPathException("The first parameter of " + getFunctionQName().getClarkName()
                            + " must be an org.apache.camel.Exchange but is a " + arg1.getObject().getClass().getName());
                }

                // 2nd argument (mandatory, index 1)
                StringValue arg2 = (StringValue) arguments[1].iterate().next();
                String headerName = arg2.getStringValue();

                // 3rd argument (mandatory, index 2)
                Item arg3 = arguments[2].iterate().next();
                String headerValue = arg3.getStringValue();

                exchange.getOut().setHeader(headerName, headerValue);

                // Don't return anything
                return SequenceTool.toLazySequence(EmptyIterator.emptyIterator());
            }
        };
    }

}