//
// nokogumbo.c defines the following:
//
//   class Nokogumbo
//     def parse(utf8_string) # returns Nokogiri::HTML::Document
//   end
//
// Processing starts by calling gumbo_parse_with_options.  The resulting
// document tree is then walked:
//
//  * if Nokogiri and libxml2 headers are available at compile time,
//    (ifdef NGLIB) then a parallel libxml2 tree is constructed, and the
//    final document is then wrapped using Nokogiri_wrap_xml_document.
//    This approach reduces memory and CPU requirements as Ruby objects
//    are only built when necessary.
//
//  * if the necessary headers are not available at compile time, Nokogiri
//    methods are called instead, producing the equivalent functionality.
//

#include <ruby.h>
#include <gumbo.h>

// class constants
static VALUE Document;

#ifdef NGLIB
#include <nokogiri.h>
#include <libxml/tree.h>

#define NIL NULL
#define CONST_CAST (xmlChar const*)
#else
#define NIL 0
#define CONST_CAST

// more class constants
static VALUE Element;
static VALUE Text;
static VALUE CDATA;
static VALUE Comment;

// interned symbols
static VALUE new;
static VALUE set_attribute;
static VALUE add_child;
static VALUE internal_subset;
static VALUE remove_;
static VALUE create_internal_subset;

// map libxml2 types to Ruby VALUE
#define xmlNodePtr VALUE
#define xmlDocPtr VALUE

// redefine libxml2 API as Ruby function calls
#define xmlNewDocNode(doc, ns, name, content) \
  rb_funcall(Element, new, 2, rb_str_new2(name), doc)
#define xmlNewProp(element, name, value) \
  rb_funcall(element, set_attribute, 2, rb_str_new2(name), rb_str_new2(value))
#define xmlNewDocText(doc, text) \
  rb_funcall(Text, new, 2, rb_str_new2(text), doc)
#define xmlNewCDataBlock(doc, content, length) \
  rb_funcall(CDATA, new, 2, rb_str_new(content, length), doc)
#define xmlNewDocComment(doc, text) \
  rb_funcall(Comment, new, 2, doc, rb_str_new2(text))
#define xmlAddChild(element, node) \
  rb_funcall(element, add_child, 1, node)
#define xmlDocSetRootElement(doc, root) \
  rb_funcall(doc, add_child, 1, root)
#define xmlCreateIntSubset(doc, name, external, system) \
  rb_funcall(doc, create_internal_subset, 3, rb_str_new2(name), \
    (external ? rb_str_new2(external) : Qnil), \
    (system ? rb_str_new2(system) : Qnil));
#define Nokogiri_wrap_xml_document(klass, doc) \
  doc

// remove internal subset from newly created documents
static VALUE xmlNewDoc(char* version) {
  VALUE doc = rb_funcall(Document, new, 0);
  rb_funcall(rb_funcall(doc, internal_subset, 0), remove_, 0);
  return doc;
}
#endif

// Build a Nokogiri Element for a given GumboElement (recursively)
static xmlNodePtr walk_tree(xmlDocPtr document, GumboElement *node) {
  // determine tag name for a given node
  xmlNodePtr element;
  if (node->tag != GUMBO_TAG_UNKNOWN) {
    element = xmlNewDocNode(document, NIL,
      CONST_CAST gumbo_normalized_tagname(node->tag), NIL);
  } else {
    GumboStringPiece tag = node->original_tag;
    gumbo_tag_from_original_text(&tag);
#ifdef _MSC_VER
    char* name = alloca(tag.length+1);
#else
    char name[tag.length+1];
#endif
    strncpy(name, tag.data, tag.length);
    name[tag.length] = '\0';
    element = xmlNewDocNode(document, NIL, CONST_CAST name, NIL);
  }

  // add in the attributes
  GumboVector* attrs = &node->attributes;
  for (int i=0; i < attrs->length; i++) {
    GumboAttribute *attr = attrs->data[i];
    xmlNewProp(element, CONST_CAST attr->name, CONST_CAST attr->value);
  }

  // add in the children
  GumboVector* children = &node->children;
  for (int i=0; i < children->length; i++) {
    GumboNode* child = children->data[i];

    xmlNodePtr node = NIL;

    switch (child->type) {
      case GUMBO_NODE_ELEMENT:
        node = walk_tree(document, &child->v.element);
        break;
      case GUMBO_NODE_WHITESPACE:
      case GUMBO_NODE_TEXT:
        node = xmlNewDocText(document, CONST_CAST child->v.text.text);
        break;
      case GUMBO_NODE_CDATA:
        node = xmlNewCDataBlock(document, 
          CONST_CAST child->v.text.original_text.data,
          (int) child->v.text.original_text.length);
        break;
      case GUMBO_NODE_COMMENT:
        node = xmlNewDocComment(document, CONST_CAST child->v.text.text);
        break;
      case GUMBO_NODE_DOCUMENT:
        break; // should never happen -- ignore
    }

    if (node) xmlAddChild(element, node);
  }

  return element;
}

// Parse a string using gumbo_parse into a Nokogiri document
static VALUE parse(VALUE self, VALUE string) {
  GumboOutput *output = gumbo_parse_with_options(
    &kGumboDefaultOptions, RSTRING_PTR(string),
    (size_t) RSTRING_LEN(string)
  );
  xmlDocPtr doc = xmlNewDoc(CONST_CAST "1.0");
  xmlNodePtr root = walk_tree(doc, &output->root->v.element);
  xmlDocSetRootElement(doc, root);
  if (output->document->v.document.has_doctype) {
    const char *public = output->document->v.document.public_identifier;
    const char *system = output->document->v.document.system_identifier;
    xmlCreateIntSubset(doc, CONST_CAST "html",
      (strlen(public) ? CONST_CAST public : NIL),
      (strlen(system) ? CONST_CAST system : NIL));
  }
  gumbo_destroy_output(&kGumboDefaultOptions, output);

  return Nokogiri_wrap_xml_document(Document, doc);
}

// Initialize the Nokogumbo class and fetch constants we will use later
void Init_nokogumboc() {
  rb_funcall(rb_mKernel, rb_intern("gem"), 1, rb_str_new2("nokogiri"));
  rb_require("nokogiri");

  // class constants
  VALUE Nokogiri = rb_const_get(rb_cObject, rb_intern("Nokogiri"));
  VALUE HTML = rb_const_get(Nokogiri, rb_intern("HTML"));
  Document = rb_const_get(HTML, rb_intern("Document"));

#ifndef NGLIB
  // more class constants
  VALUE XML = rb_const_get(Nokogiri, rb_intern("XML"));
  Element = rb_const_get(XML, rb_intern("Element"));
  Text = rb_const_get(XML, rb_intern("Text"));
  CDATA = rb_const_get(XML, rb_intern("CDATA"));
  Comment = rb_const_get(XML, rb_intern("Comment"));

  // interned symbols
  new = rb_intern("new");
  set_attribute = rb_intern("set_attribute");
  add_child = rb_intern("add_child");
  internal_subset = rb_intern("internal_subset");
  remove_ = rb_intern("remove");
  create_internal_subset = rb_intern("create_internal_subset");
#endif

  // define Nokogumbo class with a singleton parse method
  VALUE Gumbo = rb_define_class("Nokogumbo", rb_cObject);
  rb_define_singleton_method(Gumbo, "parse", parse, 1);
}