#include "debug.h"
#include <libxslt/extensions.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>

#define COW_URI ((const xmlChar *)"http://www.csclub.uwaterloo.ca/cow")

/* return the term ({Winter,Summer,Fall} YYYY) for a date in
 * YYYY-MM-DD format.
 */
void extension_cow_term(xmlXPathParserContextPtr ctxt,
                           int nargs)
{
  xmlChar *str, *ret;
  int month;
  
  if (nargs != 1) {
    xmlXPathSetArityError(ctxt);
  }
  str = xmlXPathPopString(ctxt);

  month = (str[5] - '0')*10 + (str[6] - '0');

  ret = xmlUTF8Strndup((const xmlChar*)(month < 9 ? (month < 5 ? "Winter " : "Spring ") : "Fall "), 7);
  ret = xmlStrcat(ret, xmlUTF8Strsub(str, 0, 4));
  
  xmlXPathReturnString(ctxt, ret);
  xmlFree(str);
}

void *extension_init_func(xsltTransformContextPtr ctxt,
                          const xmlChar *URI)
{
  return 0;
}

void extension_shutdown_func(xsltTransformContextPtr ctxt,
                                    const xmlChar *URI,
                                    void *data)
{
}

void init_extensions()
{
  xsltRegisterExtModule(COW_URI,
                        extension_init_func, extension_shutdown_func);
  xsltRegisterExtModuleFunction((const xmlChar*)"term", COW_URI,
                          extension_cow_term);
}