/**
 * Copyright (c) 2006-2012 LOVE Development Team
 *
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 **/

#include "ShaderEffect.h"
#include "Graphics.h"

namespace
{
// temporarily attaches a shader program (for setting uniforms, etc)
// reattaches the originally active program when destroyed
struct TemporaryAttacher
{
	TemporaryAttacher(love::graphics::opengl::ShaderEffect *sp)
	: cureffect(sp)
	, preveffect(love::graphics::opengl::ShaderEffect::current)
	{
		cureffect->attach(true);
	}
	
	~TemporaryAttacher()
	{
		if (preveffect != NULL)
			preveffect->attach();
		else
			love::graphics::opengl::ShaderEffect::detach();
	}
	
	love::graphics::opengl::ShaderEffect *cureffect;
	love::graphics::opengl::ShaderEffect *preveffect;
};
} // anonymous namespace

namespace love
{
namespace graphics
{
namespace opengl
{

ShaderEffect *ShaderEffect::current = NULL;

GLint ShaderEffect::_max_texture_units = 0;
std::vector<int> ShaderEffect::_texture_id_counters;

ShaderEffect::ShaderEffect(const std::vector<ShaderSource> &shadersources)
	: _shadersources(shadersources)
	, _program(0)
{
	if (shadersources.size() == 0)
		throw love::Exception("Cannot create shader effect: no source code!");
	
	GLint maxtextureunits;
	glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &maxtextureunits);
	_max_texture_units = std::max(maxtextureunits - 1, 0);
	
	// initialize global texture id counters if needed
	if (_texture_id_counters.size() < (size_t) _max_texture_units)
		_texture_id_counters.resize(_max_texture_units, 0);
	
	// load shader source and create program object
	loadVolatile();
}

ShaderEffect::~ShaderEffect()
{
	if (current == this)
		detach();
	
	unloadVolatile();
}

GLuint ShaderEffect::createShader(const ShaderSource &source)
{
	GLenum shadertype;
	const char *shadertypename = NULL;
	
	switch (source.type)
	{
	case TYPE_VERTEX:
		shadertype = GL_VERTEX_SHADER;
		shadertypename = "vertex";
		break;
	case TYPE_TESSCONTROL:
		shadertype = GL_TESS_CONTROL_SHADER;
		shadertypename = "tesselation control";
		break;
	case TYPE_TESSEVAL:
		shadertype = GL_TESS_EVALUATION_SHADER;
		shadertypename = "tesselation evaluation";
		break;
	case TYPE_GEOMETRY:
		shadertype = GL_GEOMETRY_SHADER;
		shadertypename = "geometry";
		break;
	case TYPE_FRAGMENT:
		shadertype = GL_FRAGMENT_SHADER;
		shadertypename = "fragment";
		break;
	default:
		throw love::Exception("Cannot create shader object: unknown shader type.");
		break;
	}
	
	// clear existing errors
	while (glGetError() != GL_NO_ERROR);
	
	GLuint shaderid = glCreateShader(shadertype);
	
	if (shaderid == 0) // oh no!
	{
		GLenum err = glGetError();
		
		if (err == GL_INVALID_OPERATION) // should only happen between glBegin() and glEnd()
			throw love::Exception("Cannot create %s shader object.", shadertypename);
		else if (err == GL_INVALID_ENUM) // invalid or unsupported shader type
			throw love::Exception("Cannot create %s shader object: %s shaders not supported.", shadertypename, shadertypename);
	}
	
	const char *src = source.code.c_str();
	size_t srclen = source.code.length();
	glShaderSource(shaderid, 1, (const GLchar **)&src, (GLint *)&srclen);
	
	glCompileShader(shaderid);
	
	GLint compile_status;
	glGetShaderiv(shaderid, GL_COMPILE_STATUS, &compile_status);
	
	if (compile_status == GL_FALSE)
	{
		GLint infologlen;
		glGetShaderiv(shaderid, GL_INFO_LOG_LENGTH, &infologlen);
		
		GLchar *errorlog = new GLchar[infologlen + 1];
		glGetShaderInfoLog(shaderid, infologlen, NULL, errorlog);
		
		std::string tmp(errorlog);
		
		delete[] errorlog;
		glDeleteShader(shaderid);
		
		throw love::Exception("Cannot compile %s shader:\n%s", shadertypename, tmp.c_str());
	}
	
	return shaderid;
}

void ShaderEffect::createProgram(const std::vector<GLuint> &shaderids)
{
	_program = glCreateProgram();
	if (_program == 0) // should only fail when called between glBegin() and glEnd()
		throw love::Exception("Cannot create shader program object.");
	
	std::vector<GLuint>::const_iterator it;
	for (it = shaderids.begin(); it != shaderids.end(); ++it)
		glAttachShader(_program, *it);
	
	glLinkProgram(_program);
	
	for (it = shaderids.begin(); it != shaderids.end(); ++it)
		glDeleteShader(*it); // flag shaders for auto-deletion when program object is deleted
	
	GLint link_ok;
	glGetProgramiv(_program, GL_LINK_STATUS, &link_ok);
	
	if (link_ok == GL_FALSE)
	{
		const std::string warnings = getWarnings();
		glDeleteProgram(_program);
		
		throw love::Exception("Cannot link shader program object:\n%s", warnings.c_str());
	}
}

bool ShaderEffect::loadVolatile()
{
	// zero out texture id list
	_texture_id_list.clear();
	_texture_id_list.insert(_texture_id_list.begin(), _max_texture_units, 0);
	
	std::vector<GLuint> shaderids;
	
	std::vector<ShaderSource>::const_iterator source;
	for (source = _shadersources.begin(); source != _shadersources.end(); ++source)
		shaderids.push_back(createShader(*source));
	
	if (shaderids.size() == 0)
		throw love::Exception("Cannot create shader effect: no valid source code!");
	
	createProgram(shaderids);
	
	if (current == this)
	{
		current = NULL; // make sure glUseProgram gets called
		attach();
	}

	return true;
}

void ShaderEffect::unloadVolatile()
{
	if (current == this)
		glUseProgram(0);
	
	if (_program != 0)
		glDeleteProgram(_program);
	
	_program = 0;
	
	// decrement global texture id counters for texture units which had textures bound from this shader
	for (size_t i = 0; i < _texture_id_list.size(); ++i)
	{
		if (_texture_id_list[i] == 0)
			continue;
		
		_texture_id_counters[i] = std::max(_texture_id_counters[i] - 1, 0);
	}
	
	// texture list is probably invalid, clear it
	_texture_id_list.clear();
	_texture_id_list.insert(_texture_id_list.begin(), _max_texture_units, 0);
	
	// same with uniform location list
	_uniforms.clear();
}

std::string ShaderEffect::getGLSLVersion()
{
	// GL_SHADING_LANGUAGE_VERSION may not be available in OpenGL < 2.0.
	const char *tmp = (const char*)glGetString(GL_SHADING_LANGUAGE_VERSION);
	if (NULL == tmp)
		return "0.0";

	// the version string always begins with a version number of the format
	//   major_number.minor_number
	// or
	//   major_number.minor_number.release_number
	// we can keep release_number, since it does not affect the check below.
	std::string versionString(tmp);
	size_t minorEndPos = versionString.find(' ');
	return versionString.substr(0, minorEndPos);
}

bool ShaderEffect::isSupported()
{
	return GLEE_VERSION_2_0 && getGLSLVersion() >= "1.2";
}

std::string ShaderEffect::getWarnings() const
{
	GLint strlen, nullpos;
	glGetProgramiv(_program, GL_INFO_LOG_LENGTH, &strlen);
	char *temp_str = new char[strlen+1];
	// be extra sure that the error string will be 0-terminated
	memset(temp_str, '\0', strlen+1);
	glGetProgramInfoLog(_program, strlen, &nullpos, temp_str);
	temp_str[nullpos] = '\0';

	std::string warnings(temp_str);
	delete[] temp_str;
	return warnings;
}

void ShaderEffect::attach(bool temporary)
{
	if (current != this)
		glUseProgram(_program);
	
	current = this;
	
	if (!temporary)
	{
		// make sure all sent textures are properly bound to their respective texture units
		// note: list potentially contains texture ids of deleted/invalid textures!
		for (size_t i = 0; i < _texture_id_list.size(); ++i)
		{
			if (_texture_id_list[i] == 0)
				continue;
			
			bindTextureToUnit(_texture_id_list[i], GL_TEXTURE0 + i + 1, false);
		}
		setActiveTextureUnit(GL_TEXTURE0);
	}
}

void ShaderEffect::detach()
{
	if (current != NULL)
		glUseProgram(0);
	
	current = NULL;
}

void ShaderEffect::sendFloat(const std::string &name, int size, const GLfloat *vec, int count)
{
	TemporaryAttacher attacher(this);
	GLint location = getUniformLocation(name);

	if (size < 1 || size > 4)
		throw love::Exception("Invalid variable size: %d (expected 1-4).", size);

	switch (size)
	{
	case 4:
		glUniform4fv(location, count, vec);
		break;
	case 3:
		glUniform3fv(location, count, vec);
		break;
	case 2:
		glUniform2fv(location, count, vec);
		break;
	case 1:
	default:
		glUniform1fv(location, count, vec);
		break;
	}

	// throw error if needed
	checkSetUniformError();
}

void ShaderEffect::sendMatrix(const std::string &name, int size, const GLfloat *m, int count)
{
	TemporaryAttacher attacher(this);
	GLint location = getUniformLocation(name);

	if (size < 2 || size > 4)
	{
		throw love::Exception("Invalid matrix size: %dx%d "
							  "(can only set 2x2, 3x3 or 4x4 matrices).", size,size);
	}

	switch (size)
	{
	case 4:
		glUniformMatrix4fv(location, count, GL_FALSE, m);
		break;
	case 3:
		glUniformMatrix3fv(location, count, GL_FALSE, m);
		break;
	case 2:
	default:
		glUniformMatrix2fv(location, count, GL_FALSE, m);
		break;
	}

	// throw error if needed
	checkSetUniformError();
}

void ShaderEffect::sendTexture(const std::string &name, GLuint texture)
{
	TemporaryAttacher attacher(this);
	GLint location = getUniformLocation(name);
	GLint texture_unit = getTextureUnit(name);
	
	// bind texture to assigned texture unit and send uniform to bound shader program
	bindTextureToUnit(texture, GL_TEXTURE0 + texture_unit, false);
	glUniform1i(location, texture_unit);
	
	// reset texture unit
	setActiveTextureUnit(GL_TEXTURE0);
	
	// increment global shader texture id counter for this texture unit, if we haven't already
	if (_texture_id_list[texture_unit-1] == 0)
		++_texture_id_counters[texture_unit-1];
	
	// store texture id so it can be re-bound to the proper texture unit when necessary
	_texture_id_list[texture_unit-1] = texture;
	
	// throw error if needed
	checkSetUniformError();
}

void ShaderEffect::sendImage(const std::string &name, const Image &image)
{
	sendTexture(name, image.getTextureName());
}

void ShaderEffect::sendCanvas(const std::string &name, const Canvas &canvas)
{
	sendTexture(name, canvas.getTextureName());
}

GLint ShaderEffect::getUniformLocation(const std::string &name)
{
	std::map<std::string, GLint>::const_iterator it = _uniforms.find(name);
	if (it != _uniforms.end())
		return it->second;

	GLint location = glGetUniformLocation(_program, name.c_str());
	if (location == -1)
	{
		throw love::Exception(
			"Cannot get location of shader variable `%s'.\n"
			"A common error is to define but not use the variable.", name.c_str());
	}

	_uniforms[name] = location;
	return location;
}

GLint ShaderEffect::getTextureUnit(const std::string &name)
{
	std::map<std::string, GLint>::const_iterator it = _texture_unit_pool.find(name);
	
	if (it != _texture_unit_pool.end())
		return it->second;
	
	int nextunitindex = 1;
	
	// prefer texture units which are unused by all other shaders
	std::vector<int>::iterator nextfreeunit = std::find(_texture_id_counters.begin(), _texture_id_counters.end(), 0);
	
	if (nextfreeunit != _texture_id_counters.end())
		nextunitindex = std::distance(_texture_id_counters.begin(), nextfreeunit) + 1; // we don't want to use unit 0
	else
	{
		// no completely unused texture units exist, try to use next free slot in our own list
		std::vector<GLuint>::iterator nexttexunit = std::find(_texture_id_list.begin(), _texture_id_list.end(), 0);
		
		if (nexttexunit == _texture_id_list.end())
			throw love::Exception("No more texture units available for shader.");
		
		nextunitindex = std::distance(_texture_id_list.begin(), nexttexunit) + 1; // we don't want to use unit 0
	}
	
	_texture_unit_pool[name] = nextunitindex;
	return nextunitindex;
}

void ShaderEffect::checkSetUniformError()
{
	GLenum error_code = glGetError();
	if (GL_INVALID_OPERATION == error_code)
	{
		throw love::Exception(
			"Invalid operation:\n"
			"- Trying to send the wrong value type to shader variable, or\n"
			"- Trying to send array values with wrong dimension, or\n"
			"- Invalid variable name.");
	}
}

} // opengl
} // graphics
} // love