/*
 * 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 "game/systems/camera-system.hpp"
#include "game/components/autofocus-component.hpp"
#include "game/components/spring-arm-component.hpp"
#include "game/components/scene-component.hpp"
#include <engine/animation/ease.hpp>
#include <engine/math/projection.hpp>
#include <engine/scene/camera.hpp>
#include <engine/math/euler-angles.hpp>
#include <execution>

camera_system::camera_system(entity::registry& registry):
	updatable_system(registry)
{}

void camera_system::update(float t, float dt)
{
	m_fixed_update_time = static_cast<double>(t);
	m_fixed_timestep = static_cast<double>(dt);
}

void camera_system::interpolate(float alpha)
{
	const double variable_update_time = m_fixed_update_time + m_fixed_timestep * static_cast<double>(alpha);
	const double variable_timestep = std::max(0.0, variable_update_time - m_variable_update_time);
	m_variable_update_time = variable_update_time;
	
	/*
	auto autofocus_group = registry.group<autofocus_component>(entt::get<scene_component>);
	std::for_each
	(
		std::execution::seq,
		autofocus_group.begin(),
		autofocus_group.end(),
		[&](auto entity_id)
		{
			auto& autofocus = autofocus_group.get<autofocus_component>(entity_id);
			auto& camera = static_cast<scene::camera&>(*autofocus_group.get<scene_component>(entity_id).object);
			
			// Clamp zoom factor
			autofocus.zoom = std::min<double>(std::max<double>(autofocus.zoom, 0.0), 1.0);
			
			// Calculate horizontal and vertical FoV
			autofocus.hfov = ease<double, double>::out_sine(autofocus.far_hfov, autofocus.near_hfov, autofocus.zoom);
			autofocus.vfov = math::vertical_fov(autofocus.hfov, static_cast<double>(camera.get_aspect_ratio()));
			
			// Calculate focal plane dimensions
			autofocus.focal_plane_size.y() = ease<double, double>::out_sine(autofocus.far_focal_plane_height, autofocus.near_focal_plane_height, autofocus.zoom);
			autofocus.focal_plane_size.x() = autofocus.focal_plane_size.y() * static_cast<double>(camera.get_aspect_ratio());
			
			// Calculate focal distance
			autofocus.focal_distance = autofocus.focal_plane_height * 0.5 / std::tan(autofocus.vfov * 0.5);
			
			// Update camera projection matrix
			camera.set_perspective(static_cast<float>(autofocus.vfov), camera.get_aspect_ratio(), camera.get_clip_near(), camera.get_clip_far());
		}
	);
	*/
	
	auto spring_arm_group = registry.group<spring_arm_component>(entt::get<scene_component>);
	std::for_each
	(
		std::execution::seq,
		spring_arm_group.begin(),
		spring_arm_group.end(),
		[&](auto entity_id)
		{
			auto& spring_arm = spring_arm_group.get<spring_arm_component>(entity_id);
			auto& camera = static_cast<scene::camera&>(*spring_arm_group.get<scene_component>(entity_id).object);
			
			math::transform<double> parent_transform = math::transform<double>::identity();
			if (spring_arm.parent_eid != entt::null)
			{
				const auto parent_scene = registry.try_get<scene_component>(spring_arm.parent_eid);
				if (parent_scene)
				{
					parent_transform.translation = math::dvec3(parent_scene->object->get_translation());
					parent_transform.rotation = math::dquat(parent_scene->object->get_rotation());
				}
			}
			
			// Calculate focal point
			spring_arm.focal_point_spring.set_target_value(parent_transform * spring_arm.focal_point_offset);
			
			// Integrate angular velocities
			spring_arm.angles_spring.set_target_value(spring_arm.angles_spring.get_target_value() + spring_arm.angular_velocities * variable_timestep);
			
			// Apply angular constraints
			spring_arm.angles_spring.set_target_value(math::clamp(spring_arm.angles_spring.get_target_value(), spring_arm.min_angles, spring_arm.max_angles));
			
			// Solve springs
			spring_arm.focal_point_spring.solve(variable_timestep);
			spring_arm.angles_spring.solve(variable_timestep);
			
			// Recalculate zoom
			// if (spring_arm.pitch_velocity)
			{
				spring_arm.zoom = ease<double, double>::in_sine(1.0, 0.0, spring_arm.angles_spring.get_value().x() / -math::half_pi<double>);
			}
			
			// Clamp zoom
			spring_arm.zoom = std::min<double>(std::max<double>(spring_arm.zoom, 0.0), 1.0);
			
			// Update FoV
			spring_arm.hfov = ease<double, double>::out_sine(spring_arm.far_hfov, spring_arm.near_hfov, spring_arm.zoom);
			spring_arm.vfov = math::vertical_fov(spring_arm.hfov, static_cast<double>(camera.get_aspect_ratio()));
			
			// Update focal plane size
			spring_arm.focal_plane_height = ease<double, double>::out_sine(spring_arm.far_focal_plane_height, spring_arm.near_focal_plane_height, spring_arm.zoom);
			spring_arm.focal_plane_width = spring_arm.focal_plane_height * static_cast<double>(camera.get_aspect_ratio());
			
			// Update focal distance
			spring_arm.focal_distance = spring_arm.focal_plane_height * 0.5 / std::tan(spring_arm.vfov * 0.5);
			
			const auto camera_up = spring_arm.up_rotation * math::dvec3{0, 1, 0};
			const auto parent_up = parent_transform.rotation * math::dvec3{0, 1, 0};
			spring_arm.up_rotation = math::normalize(math::rotation(camera_up, parent_up) * spring_arm.up_rotation);
			
			// Update camera rotation
			spring_arm.camera_rotation = math::normalize(spring_arm.up_rotation * math::euler_xyz_to_quat(spring_arm.angles_spring.get_value()));
			
			// Update transform
			const auto camera_translation = spring_arm.focal_point_spring.get_value() + spring_arm.camera_rotation * math::dvec3{0.0f, 0.0f, spring_arm.focal_distance};
			
			math::transform<float> camera_transform;
			camera_transform.translation = math::fvec3(camera_translation);
			camera_transform.rotation = math::fquat(spring_arm.camera_rotation);
			camera_transform.scale = {1, 1, 1};
			
			
			double center_offset = (1.0 - std::abs(spring_arm.angles_spring.get_value().x()) / math::half_pi<double>) * (spring_arm.focal_plane_height / 3.0 * 0.5);
			camera_transform.translation += math::fvec3(spring_arm.camera_rotation * math::dvec3{0, center_offset, 0});
			
			camera.set_transform(camera_transform);
			camera.set_perspective(static_cast<float>(spring_arm.vfov), camera.get_aspect_ratio(), camera.get_clip_near(), camera.get_clip_far());
		}
	);
}

void camera_system::set_viewport(const math::fvec4& viewport)
{
	m_viewport = math::dvec4(viewport);
	m_aspect_ratio = m_viewport[2] /  m_viewport[3];
}