/*
    Ousía
    Copyright (C) 2014, 2015  Benjamin Paaßen, Andreas Stöckel

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <iostream>

#include <expat.h>

#include <core/Utils.hpp>
#include <core/parser/ParserStack.hpp>

#include "XmlParser.hpp"

namespace ousia {
namespace parser {
namespace xml {

/* Document structure */
static const State STATE_DOCUMENT = 0;
static const State STATE_HEAD = 1;
static const State STATE_BODY = 2;

/* Special commands */
static const State STATE_USE = 100;
static const State STATE_INCLUDE = 101;
static const State STATE_INLINE = 102;

/* Type system definitions */
static const State STATE_TYPES = 200;
static const State STATE_CONSTANT = 201;
static const State STATE_ENUM = 202;
static const State STATE_STRUCT = 203;

class TestHandler : public Handler {
public:
	using Handler::Handler;

	void start(const Variant &args) override
	{
		std::cout << this->name << ": start (isChild: " << (this->isChild)
		          << ", args: " << args << ")" << std::endl;
	}

	void end() override
	{
		// TODO
	}

	void data(const std::string &data, int field) override
	{
		std::cout << this->name << ": data \"" << data << "\"" << std::endl;
	}

	void child(std::shared_ptr<Handler> handler) override
	{
		// TODO
	}
};

static Handler *createTestHandler(const ParserContext &ctx, std::string name,
                                  State state, State parentState, bool isChild)
{
	return new TestHandler{ctx, name, state, parentState, isChild};
}

static const std::multimap<std::string, HandlerDescriptor> XML_HANDLERS{
    /* Documents */
    {"document", {{STATE_NONE}, createTestHandler, STATE_DOCUMENT}},
    {"head", {{STATE_DOCUMENT}, createTestHandler, STATE_HEAD}},
    {"body", {{STATE_DOCUMENT}, createTestHandler, STATE_BODY, true}},

    /* Special commands */
    {"use", {{STATE_HEAD}, createTestHandler, STATE_USE}},
    {"include", {{STATE_ALL}, createTestHandler, STATE_INCLUDE}},
    {"inline", {{STATE_ALL}, createTestHandler, STATE_INLINE}},

    /* Typesystem definitions */
    {"typesystem", {{STATE_NONE, STATE_HEAD}, createTestHandler, STATE_TYPES}},
    {"enum", {{STATE_TYPES}, createTestHandler, STATE_ENUM}},
    {"struct", {{STATE_TYPES}, createTestHandler, STATE_STRUCT}},
    {"constant", {{STATE_TYPES}, createTestHandler, STATE_CONSTANT}}};

/**
 * Wrapper class around the XML_Parser pointer which safely frees it whenever
 * the scope is left (e.g. because an exception was thrown).
 */
class ScopedExpatXmlParser {
private:
	/**
	 * Internal pointer to the XML_Parser instance.
	 */
	XML_Parser parser;

public:
	/**
	 * Constructor of the ScopedExpatXmlParser class. Calls XML_ParserCreateNS
	 * from the expat library. Throws a parser exception if the XML parser
	 * cannot be initialized.
	 *
	 * @param encoding is the protocol-defined encoding passed to expat (or
	 * nullptr if expat should determine the encoding by itself).
	 */
	ScopedExpatXmlParser(const XML_Char *encoding) : parser(nullptr)
	{
		parser = XML_ParserCreate(encoding);
		if (!parser) {
			throw ParserException{
			    "Internal error: Could not create expat XML parser!"};
		}
	}

	/**
	 * Destuctor of the ScopedExpatXmlParser, frees the XML parser instance.
	 */
	~ScopedExpatXmlParser()
	{
		if (parser) {
			XML_ParserFree(parser);
			parser = nullptr;
		}
	}

	/**
	 * Returns the XML_Parser pointer.
	 */
	XML_Parser operator&() { return parser; }
};

/* Adapter Expat -> ParserStack */

static void xmlStartElementHandler(void *userData, const XML_Char *name,
                                   const XML_Char **attrs)
{
	Variant::mapType args;
	const XML_Char **attr = attrs;
	while (*attr) {
		const std::string key{*(attr++)};
		args.emplace(std::make_pair(key, Variant{*(attr++)}));
	}
	(static_cast<ParserStack *>(userData))->start(std::string(name), args);
}

static void xmlEndElementHandler(void *userData, const XML_Char *name)
{
	(static_cast<ParserStack *>(userData))->end();
}

static void xmlCharacterDataHandler(void *userData, const XML_Char *s, int len)
{
	const std::string data =
	    Utils::trim(std::string{s, static_cast<size_t>(len)});
	if (!data.empty()) {
		(static_cast<ParserStack *>(userData))->data(data);
	}
}

/* Class XmlParser */

std::set<std::string> XmlParser::mimetypes()
{
	return std::set<std::string>{{"text/vnd.ousia.oxm", "text/vnd.ousia.oxd"}};
}

Rooted<Node> XmlParser::parse(std::istream &is, ParserContext &ctx)
{
	// Create the parser object
	ScopedExpatXmlParser p{"UTF-8"};

	// Create the parser stack instance and pass the reference to the state
	// machine descriptor
	ParserStack stack{ctx, XML_HANDLERS};
	XML_SetUserData(&p, &stack);

	// Set the callback functions
	XML_SetStartElementHandler(&p, xmlStartElementHandler);
	XML_SetEndElementHandler(&p, xmlEndElementHandler);
	XML_SetCharacterDataHandler(&p, xmlCharacterDataHandler);

	// Feed data into expat while there is data to process
	const std::streamsize BUFFER_SIZE = 4096;  // TODO: Move to own header?
	while (true) {
		// Fetch a buffer from expat for the input data
		char *buf = static_cast<char *>(XML_GetBuffer(&p, BUFFER_SIZE));
		if (!buf) {
			throw ParserException{"Internal error: XML parser out of memory!"};
		}

		// Read the input data from the stream
		const std::streamsize bytesRead = is.read(buf, BUFFER_SIZE).gcount();

		// Parse the data and handle any XML error
		if (!XML_ParseBuffer(&p, bytesRead, bytesRead == 0)) {
			const int line = XML_GetCurrentLineNumber(&p);
			const int column = XML_GetCurrentColumnNumber(&p);
			const XML_Error code = XML_GetErrorCode(&p);
			const std::string msg = std::string{XML_ErrorString(code)};
			throw ParserException{"XML Syntax Error: " + msg, line, column,
			                      false};
		}

		// Abort once there are no more bytes in the stream
		if (bytesRead == 0) {
			break;
		}
	}

	return nullptr;
}
}
}
}