/*
 *  call-seq:
 *    transform(document, params = [])
 *
 *  Apply an XSLT stylesheet to an XML::Document.
 *  +params+ is an array of strings used as XSLT parameters.
 *  returns Nokogiri::XML::Document
 *
 *  Example:
 * 
 *    doc   = Nokogiri::XML(File.read(ARGV[0]))
 *    xslt  = Nokogiri::XSLT(File.read(ARGV[1]))
 *    puts xslt.transform(doc, ['key', 'value'])
 *
 */
static VALUE transform(int argc, VALUE* argv, VALUE self)
{
    VALUE xmldoc, paramobj ;
    xmlDocPtr xml ;
    xmlDocPtr result ;
    nokogiriXsltStylesheetTuple *wrapper;
    const char** params ;
    long param_len, j ;

    rb_scan_args(argc, argv, "11", &xmldoc, &paramobj);
    if (NIL_P(paramobj)) { paramobj = rb_ary_new2(0L) ; }
    if (!rb_obj_is_kind_of(xmldoc, cNokogiriXmlDocument))
      rb_raise(rb_eArgError, "argument must be a Nokogiri::XML::Document");

    /* handle hashes as arguments. */
    if(T_HASH == TYPE(paramobj)) {
      paramobj = rb_funcall(paramobj, rb_intern("to_a"), 0);
      paramobj = rb_funcall(paramobj, rb_intern("flatten"), 0);
    }

    Check_Type(paramobj, T_ARRAY);

    Data_Get_Struct(xmldoc, xmlDoc, xml);
    Data_Get_Struct(self, nokogiriXsltStylesheetTuple, wrapper);

    param_len = RARRAY_LEN(paramobj);
    params = calloc((size_t)param_len+1, sizeof(char*));
    for (j = 0 ; j < param_len ; j++) {
      VALUE entry = rb_ary_entry(paramobj, j);
      const char * ptr = StringValuePtr(entry);
      params[j] = ptr;
    }
    params[param_len] = 0 ;

    result = xsltApplyStylesheet(wrapper->ss, xml, params);
    free(params);

    if (!result) rb_raise(rb_eRuntimeError, "could not perform xslt transform on document");

    return Nokogiri_wrap_xml_document((VALUE)0, result) ;
}