/*
 * 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_RENDER_MATERIAL_HPP
#define ANTKEEPER_RENDER_MATERIAL_HPP

#include <cstdint>
#include <engine/gl/shader-template.hpp>
#include <engine/render/material-blend-mode.hpp>
#include <engine/render/material-variable.hpp>
#include <engine/render/material-shadow-mode.hpp>
#include <engine/utility/hash/fnv1a.hpp>
#include <unordered_map>

namespace render {

/**
 * A material is associated with exactly one shader program and contains a set of material properties which can be uploaded to that shader program via shader inputs.
 */
class material
{
public:
	/**
	 * Constructs a material.
	 */
	material() = default;
	
	/**
	 * Constructs a copy of another material.
	 *
	 * @param other Material to copy.
	 */
	material(const material& other);
	
	/**
	 * Destroys a material.
	 */
	~material() = default;
	
	/**
	 * Makes this material a copy of aother material.
	 *
	 * @param other Material to copy.
	 * @return Reference to this material.
	 */
	material& operator=(const material& other);
	
	/// @name Settings
	/// @{
	
	/**
	 * Enables or disables back-face culling of the material surface.
	 *
	 * @param two_sided `true` to disable back-face culling, or `false` to enable it.
	 */
	void set_two_sided(bool two_sided) noexcept;
	
	/**
	 * Sets the material blend mode.
	 *
	 * @param mode Blend mode.
	 */
	void set_blend_mode(material_blend_mode mode) noexcept;
	
	/**
	 * Sets the material shadow mode.
	 *
	 * @param mode Shadow mode.
	 */
	void set_shadow_mode(material_shadow_mode mode) noexcept;
	
	/**
	 * Sets the material flags.
	 *
	 * @param flags Material flags.
	 */
	void set_flags(std::uint32_t flags) noexcept;
	
	/// Returns `true` if the material surface is two-sided, and `false` otherwise.
	[[nodiscard]] inline bool is_two_sided() const noexcept
	{
		return two_sided;
	}
	
	/// Returns the material blend mode.
	[[nodiscard]] inline material_blend_mode get_blend_mode() const noexcept
	{
		return blend_mode;
	}
	
	/// Returns the material shadow mode.
	[[nodiscard]] inline material_shadow_mode get_shadow_mode() const noexcept
	{
		return shadow_mode;
	}
	
	/// Returns the material flags.
	[[nodiscard]] inline std::uint32_t get_flags() const noexcept
	{
		return flags;
	}
	
	/// @}
	
	/// @name Shading
	/// @{
	
	/**
	 * Sets the material's shader template.
	 *
	 * @param shader_template Shader template with which to associate the material.
	 */
	void set_shader_template(std::shared_ptr<gl::shader_template> shader_template);
	
	/**
	 * Returns the shader template with which this material is associated.
	 */
	[[nodiscard]] inline const std::shared_ptr<gl::shader_template>& get_shader_template() const noexcept
	{
		return shader_template;
	}
	
	/**
	 * Sets the value of a material variable with the given name.
	 *
	 * @param key 32-bit FNV-1a hash value of the variable name.
	 * @param value Shared pointer to the material variable value.
	 */
	void set_variable(hash::fnv1a32_t key, std::shared_ptr<material_variable_base> value);
	
	/**
	 * Returns a shared pointer to the material variable with the given name, or `nullptr` if not found.
	 *
	 * @param key 32-bit FNV-1a hash value of the variable name.
	 *
	 * @return Shared pointer to the material variable with the given name, or `nullptr` if not found.
	 */
	[[nodiscard]] std::shared_ptr<material_variable_base> get_variable(hash::fnv1a32_t key) const;
	
	/**
	 * Returns all material variables.
	 *
	 * @return Map of 32-bit FNV-1a hash values of variable names to variables.
	 */
	[[nodiscard]] inline const std::unordered_map<hash::fnv1a32_t, std::shared_ptr<material_variable_base>>& get_variables() const noexcept
	{
		return variable_map;
	}
	
	/// @}
	
	/**
	 * Returns a hash of the material state.
	 *
	 * The followings functions may change the material hash:
	 *
	 * * material::set_shader_template
	 * * material::set_flags
	 * * material::set_blend_mode
	 * * material::set_two_sided
	 * * material::set_shadow_mode
	 */
	[[nodiscard]] inline std::size_t hash() const noexcept
	{
		return m_hash;
	}
	
private:
	/**
	 * Recalculates the material state hash.
	 */
	void rehash() noexcept;
	
	bool two_sided{false};
	material_blend_mode blend_mode{material_blend_mode::opaque};
	material_shadow_mode shadow_mode{material_shadow_mode::opaque};
	std::uint32_t flags{0};
	std::shared_ptr<gl::shader_template> shader_template;
	std::unordered_map<hash::fnv1a32_t, std::shared_ptr<material_variable_base>> variable_map;
	std::size_t m_hash{0};
};

} // namespace render

#endif // ANTKEEPER_RENDER_MATERIAL_HPP