/*
 * 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/>.
 */

#ifndef ANTKEEPER_GL_SHADER_PROGRAM_HPP
#define ANTKEEPER_GL_SHADER_PROGRAM_HPP

#include <string>
#include <unordered_map>
#include <unordered_set>
#include <cstdint>
#include <memory>
#include <engine/utility/hash/fnv1a.hpp>

namespace gl {

class shader_object;
class shader_variable;

/**
 * Shader program which can be linked to shader objects and executed.
 *
 * @see gl::shader_object
 */
class shader_program
{
public:
	/**
	 * Creates an empty shader program.
	 *
	 * @exception std::runtime_error An error occurred while creating an OpenGL shader program.
	 */
	shader_program();
	
	/**
	 * Destroys a shader program.
	 */
	~shader_program();
	
	shader_program(const shader_program&) = delete;
	shader_program(shader_program&&) = delete;
	shader_program& operator=(const shader_program&) = delete;
	shader_program& operator=(shader_program&&) = delete;
	
	/**
	 * Attaches a shader object to the shader program. Attaching a shader object has no effect on a shader program until shader_program::link() is called.
	 *
	 * @param object Shader object to attach.
	 *
	 * @exception std::runtime_error Shader object is already attached to the shader program.
	 * @exception std::runtime_error OpenGL shader program is not a valid program object.
	 * @exception std::runtime_error OpenGL shader object is not a valid shader object.
	 * @exception std::runtime_error OpenGL shader object is already attached to the shader program.
	 *
	 * @see shader_program::link()
	 */
	void attach(const shader_object& object);
	
	/**
	 * Detaches a shader object from the shader program. Detaching a shader object has no effect on a shader program until shader_program::link() is called.
	 *
	 * @param object Shader object to detach.
	 *
	 * @exception std::runtime_error Shader object is not attached to the shader program.
	 * @exception std::runtime_error OpenGL shader program is not a valid program object.
	 * @exception std::runtime_error OpenGL shader object is not a valid shader object.
	 * @exception std::runtime_error OpenGL shader object is not attached to the shader program.
	 *
	 * @see shader_program::link()
	 */
	void detach(const shader_object& object);
	
	/**
	 * Detaches all shader objects from the shader program.
	 *
	 * @exception std::runtime_error Shader object is not attached to the shader program.
	 * @exception std::runtime_error OpenGL shader program is not a valid program object.
	 * @exception std::runtime_error OpenGL shader object is not a valid shader object.
	 * @exception std::runtime_error OpenGL shader object is not attached to the shader program.
	 *
	 * @see shader_program::detach(const shader_object*)
	 */
	void detach_all();
	
	/**
	 * Links all attached shader objects to create an executable shader program.
	 *
	 * @return `true` if the attached shader objects were successfully linked into the shader program, `false` otherwise.
	 *
	 * @warning All existing of the shader program's variables will be invalidated if the program is re-linked.
	 */
	bool link();
	
	/// Returns `true` if the shader program has been successfully linked, `false` otherwise.
	[[nodiscard]] inline bool linked() const noexcept
	{
		return m_linked;
	}
	
	/**
	 * Returns all active shader variables in the shader program.
	 *
	 * @return Map of 32-bit FNV-1a hash values of shader variable names to shader variables.
	 */
	[[nodiscard]] inline const std::unordered_map<hash::fnv1a32_t, const std::unique_ptr<const shader_variable>>& variables() const noexcept
	{
		return variable_map;
	}
	
	/**
	 * Returns a pointer to an active shader variable with the given name, or `nullptr` if not found.
	 *
	 * @param key 32-bit FNV-1a hash value of a shader variable name.
	 *
	 * @return Pointer to the active shader variable with the given name, or `nullptr` if not found.
	 */
	[[nodiscard]] inline const shader_variable* variable(hash::fnv1a32_t key) const
	{
		if (auto i = variable_map.find(key); i != variable_map.end())
		{
			return i->second.get();
		}
		
		return nullptr;
	}
	
	/**
	 * Returns the info log that contains debug information when linking fails.
	 */
	[[nodiscard]] inline const std::string& info() const noexcept
	{
		return info_log;
	}

private:
	friend class pipeline;
	
	void load_variables();
	
	unsigned int gl_program_id{0};
	bool m_linked{false};
	std::unordered_set<const shader_object*> attached_objects;
	std::unordered_map<hash::fnv1a32_t, const std::unique_ptr<const shader_variable>> variable_map;
	std::string info_log;
};

} // namespace gl

#endif // ANTKEEPER_GL_SHADER_PROGRAM_HPP