/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code 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.
 *
 * Antkeeper source code 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 Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <engine/gl/shader-program.hpp>
#include <engine/gl/shader-object.hpp>
#include <engine/gl/opengl/gl-shader-variables.hpp>
#include <glad/gl.h>
#include <stdexcept>
#include <string_view>

namespace gl {

shader_program::shader_program()
{
	// Create an OpenGL shader program
	gl_program_id = glCreateProgram();
	
	// Handle OpenGL errors
	if (!gl_program_id)
	{
		throw std::runtime_error("Unable to create OpenGL shader program");
	}
}

shader_program::~shader_program()
{
	// Detach all shader objects
	detach_all();
	
	// Delete the OpenGL shader program
	glDeleteProgram(gl_program_id);
}

void shader_program::attach(const shader_object& object)
{
	if (attached_objects.find(&object) != attached_objects.end())
	{
		throw std::runtime_error("OpenGL shader object already attached to the shader program");
	}
	else
	{
		// Check that both the OpenGL shader program and OpenGL shader object are valid
		if (glIsProgram(gl_program_id) != GL_TRUE)
		{
			throw std::runtime_error("Invalid OpenGL shader program");
		}
		if (glIsShader(object.gl_shader_id) != GL_TRUE)
		{
			throw std::runtime_error("Invalid OpenGL shader object");
		}
		
		// Attach the OpenGL shader object to the OpenGL shader program
		glAttachShader(gl_program_id, object.gl_shader_id);
		
		// Add shader object to set of attached objects
		attached_objects.insert(&object);
	}
}

void shader_program::detach(const shader_object& object)
{
	if (attached_objects.find(&object) == attached_objects.end())
	{
		throw std::runtime_error("Shader object is not attached to the shader program.");
	}
	else
	{
		// Check that both the OpenGL shader program and OpenGL shader object are valid
		if (glIsProgram(gl_program_id) != GL_TRUE)
		{
			throw std::runtime_error("Invalid OpenGL shader program");
		}
		if (glIsShader(object.gl_shader_id) != GL_TRUE)
		{
			throw std::runtime_error("Invalid OpenGL shader object");
		}
		
		// Detach the OpenGL shader object from the OpenGL shader program
		glDetachShader(gl_program_id, object.gl_shader_id);
		
		// Remove shader object from set of attached objects
		attached_objects.erase(&object);
	}
}

void shader_program::detach_all()
{
	while (!attached_objects.empty())
	{
		detach(**attached_objects.begin());
	}
}

bool shader_program::link()
{
	m_linked = false;
	info_log.clear();
	variable_map.clear();
	
	// Check that the OpenGL shader program is valid
	if (glIsProgram(gl_program_id) != GL_TRUE)
	{
		throw std::runtime_error("Invalid OpenGL shader program");
	}
	
	// Link OpenGL shader program
	glLinkProgram(gl_program_id);
	
	// Get OpenGL shader program linking status
	GLint gl_link_status;
	glGetProgramiv(gl_program_id, GL_LINK_STATUS, &gl_link_status);
	m_linked = (gl_link_status == GL_TRUE);
	
	// Populate info log string
	if (m_linked)
	{
		// Load shader variables
		load_variables();
	}
	else
	{
		// Get OpenGL shader program info log length
		GLint gl_info_log_length;
		glGetProgramiv(gl_program_id, GL_INFO_LOG_LENGTH, &gl_info_log_length);
		
		if (gl_info_log_length > 0)
		{
			// Resize string to accommodate OpenGL shader program info log
			info_log.resize(gl_info_log_length);
			
			// Read OpenGL shader program info log into string
			glGetProgramInfoLog(gl_program_id, gl_info_log_length, &gl_info_log_length, info_log.data());
			
			// Remove redundant null terminator from string
			info_log.pop_back();
		}
	}
	
	return m_linked;
}

void shader_program::load_variables()
{
	variable_map.clear();
	
	// Get maximum uniform name length
	GLint max_uniform_name_length = 0;
	glGetProgramiv(gl_program_id, GL_ACTIVE_UNIFORM_MAX_LENGTH, &max_uniform_name_length);
	
	// Allocate uniform name buffer
	std::string uniform_name(static_cast<std::size_t>(max_uniform_name_length), '\0');
	
	// Get number of active uniforms in the shader
	GLint active_uniform_count = 0;
	glGetProgramiv(gl_program_id, GL_ACTIVE_UNIFORMS, &active_uniform_count);
	
	// Init texture unit index
	GLint texture_index = 0;
	
	// For each active uniform
	for (GLint uniform_index = 0; uniform_index < active_uniform_count; ++uniform_index)
	{
		// Get uniform info
		GLsizei uniform_name_length;
		GLint uniform_size;
		GLenum uniform_type;
		glGetActiveUniform(gl_program_id, static_cast<GLuint>(uniform_index), static_cast<GLsizei>(max_uniform_name_length), &uniform_name_length, &uniform_size, &uniform_type, uniform_name.data());
		
		// Get uniform location
		const GLint uniform_location = glGetUniformLocation(gl_program_id, uniform_name.c_str());
		if (uniform_location == -1)
		{
			throw std::runtime_error("Unable to get shader uniform location");
		}
		
		// Get length of variable name by stripping array notation from uniform name
		std::size_t uniform_base_name_length = static_cast<std::size_t>(uniform_name_length);
		if (std::size_t i = std::string_view(uniform_name.c_str(), uniform_name_length).find_first_of("["); i != std::string::npos)
		{
			uniform_base_name_length = i;
		}
		
		// Hash variable name to get variable key
		const hash::fnv1a32_t variable_key = hash::fnv1a32<char>({uniform_name.c_str(), uniform_base_name_length});
		
		// Get size of variable
		const std::size_t variable_size = static_cast<std::size_t>(uniform_size);
		
		// Construct shader variable
		std::unique_ptr<const gl::shader_variable> variable;
		switch (uniform_type)
		{
			case GL_BOOL:
				variable = std::make_unique<const gl_shader_bool>(variable_size, uniform_location);
				break;
			case GL_BOOL_VEC2:
				variable = std::make_unique<const gl_shader_bvec2>(variable_size, uniform_location);
				break;
			case GL_BOOL_VEC3:
				variable = std::make_unique<const gl_shader_bvec3>(variable_size, uniform_location);
				break;
			case GL_BOOL_VEC4:
				variable = std::make_unique<const gl_shader_bvec4>(variable_size, uniform_location);
				break;
			
			case GL_INT:
				variable = std::make_unique<const gl_shader_int>(variable_size, uniform_location);
				break;
			case GL_INT_VEC2:
				variable = std::make_unique<const gl_shader_ivec2>(variable_size, uniform_location);
				break;
			case GL_INT_VEC3:
				variable = std::make_unique<const gl_shader_ivec3>(variable_size, uniform_location);
				break;
			case GL_INT_VEC4:
				variable = std::make_unique<const gl_shader_ivec4>(variable_size, uniform_location);
				break;
			
			case GL_UNSIGNED_INT:
				variable = std::make_unique<const gl_shader_uint>(variable_size, uniform_location);
				break;
			case GL_UNSIGNED_INT_VEC2:
				variable = std::make_unique<const gl_shader_uvec2>(variable_size, uniform_location);
				break;
			case GL_UNSIGNED_INT_VEC3:
				variable = std::make_unique<const gl_shader_uvec3>(variable_size, uniform_location);
				break;
			case GL_UNSIGNED_INT_VEC4:
				variable = std::make_unique<const gl_shader_uvec4>(variable_size, uniform_location);
				break;
			
			case GL_FLOAT:
				variable = std::make_unique<const gl_shader_float>(variable_size, uniform_location);
				break;
			case GL_FLOAT_VEC2:
				variable = std::make_unique<const gl_shader_fvec2>(variable_size, uniform_location);
				break;
			case GL_FLOAT_VEC3:
				variable = std::make_unique<const gl_shader_fvec3>(variable_size, uniform_location);
				break;
			case GL_FLOAT_VEC4:
				variable = std::make_unique<const gl_shader_fvec4>(variable_size, uniform_location);
				break;
			
			case GL_FLOAT_MAT2:
				variable = std::make_unique<const gl_shader_fmat2>(variable_size, uniform_location);
				break;
			case GL_FLOAT_MAT3:
				variable = std::make_unique<const gl_shader_fmat3>(variable_size, uniform_location);
				break;
			case GL_FLOAT_MAT4:
				variable = std::make_unique<const gl_shader_fmat4>(variable_size, uniform_location);
				break;
			
			case GL_SAMPLER_1D:
			case GL_SAMPLER_1D_SHADOW:
				variable = std::make_unique<const gl_shader_texture_1d>(variable_size, uniform_location, texture_index);
				texture_index += uniform_size;
				break;
			
			case GL_SAMPLER_2D:
			case GL_SAMPLER_2D_SHADOW:
				variable = std::make_unique<const gl_shader_texture_2d>(variable_size, uniform_location, texture_index);
				texture_index += uniform_size;
				break;
			
			case GL_SAMPLER_3D:
				variable = std::make_unique<const gl_shader_texture_3d>(variable_size, uniform_location, texture_index);
				texture_index += uniform_size;
				break;
			
			case GL_SAMPLER_CUBE:
				variable = std::make_unique<const gl_shader_texture_cube>(variable_size, uniform_location, texture_index);
				texture_index += uniform_size;
				break;
			
			default:
				throw std::runtime_error("Unsupported to shader uniform type");
				break;
		}
		
		// Map variable to variable key
		variable_map.emplace(variable_key, std::move(variable));
	}
}

} // namespace gl