#include <psemek/app/app.hpp>
#include <psemek/app/main.hpp>
#include <psemek/gfx/painter.hpp>
#include <psemek/geom/orthographic.hpp>
#include <psemek/random/device.hpp>
#include <psemek/random/generator.hpp>
#include <psemek/random/uniform_ball.hpp>
#include <psemek/cg/triangulation/delaunay.hpp>
#include <psemek/util/clock.hpp>
#include <psemek/prof/profiler.hpp>
#include <psemek/app/ui_scene.hpp>
#include <psemek/ui/button.hpp>
#include <psemek/ui/slider.hpp>
#include <psemek/ui/default_element_factory.hpp>
#include <psemek/ui/frame.hpp>
#include <psemek/ui/window.hpp>
#include <psemek/ui/screen.hpp>
#include <psemek/ui/grid_layout.hpp>
#include <psemek/ui/event_interceptor.hpp>
#include <psemek/util/to_string.hpp>
#include <psemek/util/recursive.hpp>

#include <vector>

using namespace psemek;

struct main_scene
	: app::ui_scene
{
	main_scene(ui::controller & ui_controller);

	void update() override;
	void present() override;

	float simulation_radius = 1.f;
	float simulation_radius_tgt = 1.f;

	float potential = 1000.f;
	float step = 1e-4f;
	float multipole_threshold = 2.f;

	random::generator rng{random::device{}};

	std::vector<geom::point<float, 2>> points;
	std::vector<geom::segment<std::uint32_t>> edges;
	std::vector<std::uint32_t> degree;

	gfx::painter painter;

	util::clock<> clock;
};

main_scene::main_scene(ui::controller & ui_controller)
	: app::ui_scene(ui_controller)
{
	ui::default_element_factory element_factory;

	auto root = element_factory.make_screen();

	auto wheel_event = std::make_shared<ui::event_interceptor>();
	wheel_event->on_mouse_wheel([this](ui::mouse_wheel const & event){
		simulation_radius_tgt *= std::pow(0.8f, event.delta);
		return true;
	});
	wheel_event->set_child(element_factory.make_screen());
	root->add_child(wheel_event, ui::screen::x_policy::fill, ui::screen::y_policy::fill);

	auto panel = element_factory.make_window("");
	panel->caption()->set_tagged_text("[bold][uline]Options[/uline][/bold]");
	root->add_child(panel, ui::screen::x_policy::floating, ui::screen::y_policy::floating);

	auto layout = element_factory.make_grid_layout();
	panel->set_child(layout);

	auto count_name_label = element_factory.make_label("Count:");
	count_name_label->set_valign(ui::label::valignment::center);
	count_name_label->set_halign(ui::label::halignment::right);
	auto count_value_label = element_factory.make_label("");
	count_value_label->set_valign(ui::label::valignment::center);
	count_value_label->set_halign(ui::label::halignment::center);

	auto count_slider = element_factory.make_slider();
	count_slider->set_value_range({1, 5000}, false);
	count_slider->on_value_changed([this, count_value_label](int value){
		count_value_label->set_text(util::to_string(value));

		if (value < points.size())
			points.resize(value);
		else
		{
			float radius = std::max(0.5f, std::sqrt((points.size() + value) / 1000.f));

			random::uniform_sphere_point_distribution<float, 2> d({0.f, 0.f}, radius * 1.25f);
			while (points.size() < value)
				points.push_back(d(rng));
		}
	});
	count_slider->set_value(100);

	auto step_name_label = element_factory.make_label("Step:");
	step_name_label->set_valign(ui::label::valignment::center);
	step_name_label->set_halign(ui::label::halignment::right);
	auto step_value_label = element_factory.make_label("");
	step_value_label->set_valign(ui::label::valignment::center);
	step_value_label->set_halign(ui::label::halignment::center);

	auto step_slider = element_factory.make_slider();
	step_slider->set_value_range({0, 12}, false);
	step_slider->on_value_changed([this, step_value_label](int value){
		step = std::pow(2.f, value - 20);
		step_value_label->set_text(util::to_string(std::setprecision(1), std::scientific, step));
	});
	step_slider->set_value(11);

	auto precision_name_label = element_factory.make_label("Precision:");
	precision_name_label->set_valign(ui::label::valignment::center);
	precision_name_label->set_halign(ui::label::halignment::right);
	auto precision_value_label = element_factory.make_label("");
	precision_value_label->set_valign(ui::label::valignment::center);
	precision_value_label->set_halign(ui::label::halignment::center);

	auto precision_slider = element_factory.make_slider();
	precision_slider->set_value_range({5, 50}, false);
	precision_slider->on_value_changed([this, precision_value_label](int value){
		multipole_threshold = value * 0.1f;
		precision_value_label->set_text(util::to_string(std::setprecision(1), std::fixed, multipole_threshold));
	});
	precision_slider->set_value(15);

	layout->set_size(3, 3);
	layout->set_column_weight(0, 0.5f);
	layout->set_column_weight(1, 0.5f);
	layout->set(0, 0, count_name_label);
	layout->set(0, 1, count_value_label);
	layout->set(0, 2, count_slider);
	layout->set(1, 0, step_name_label);
	layout->set(1, 1, step_value_label);
	layout->set(1, 2, step_slider);
	layout->set(2, 0, precision_name_label);
	layout->set(2, 1, precision_value_label);
	layout->set(2, 2, precision_slider);

	ui::style style;
	style.font = ui::make_default_9x12_font();
	style.bold_font = ui::make_default_10x12_bold_font();
	style.text_scale = 1;
	style.bg_color = gfx::color_rgba{127, 127, 191, 255};
	style.fg_color = gfx::color_rgba{127, 127, 255, 255};
	style.action_color = gfx::color_rgba{0, 0, 255, 255};
	style.highlight_color = gfx::color_rgba{0, 255, 255, 255};
	style.border_width = 0;
	style.bevel_width = 0;
	root->set_style(std::make_shared<ui::style>(std::move(style)));

	set_ui(root);
}

struct node
{
	static constexpr std::uint32_t null = -1;

	float size;
	float mass = 0.f;
	geom::point<float, 2> center = geom::point<float, 2>::zero();

	std::uint32_t children[2][2] {{null, null}, {null, null}};
};

void main_scene::update()
{
	ui_scene::update();

	float const dt = clock.restart().count();
	const int iterations = 1;
	auto const origin = geom::point<float, 2>::zero();

	std::vector<node> nodes;
	std::uint32_t root;

	auto add_node = util::recursive([&](auto && self, geom::box<float, 2> const & bbox, auto begin, auto end) -> std::uint32_t
	{
		if (begin == end)
			return node::null;

		std::uint32_t id = nodes.size();
		nodes.emplace_back().size = bbox[0].length();

		if (end - begin > 1)
		{
			auto middle_x = bbox[0].center();
			auto middle_y = bbox[1].center();

			auto mid_it = std::partition(begin, end, [middle_x](auto const & p){ return p[0] < middle_x; });
			auto left_mid_it = std::partition(begin, mid_it, [middle_y](auto const & p){ return p[1] < middle_y; });
			auto right_mid_it = std::partition(mid_it, end, [middle_y](auto const & p){ return p[1] < middle_y; });

			nodes[id].children[0][0] = self(geom::box<float, 2>{{{bbox[0].min, middle_x}, {bbox[1].min, middle_y}}}, begin, left_mid_it);
			nodes[id].children[0][1] = self(geom::box<float, 2>{{{bbox[0].min, middle_x}, {middle_y, bbox[1].max}}}, left_mid_it, mid_it);
			nodes[id].children[1][0] = self(geom::box<float, 2>{{{middle_x, bbox[0].max}, {bbox[1].min, middle_y}}}, mid_it, right_mid_it);
			nodes[id].children[1][1] = self(geom::box<float, 2>{{{middle_x, bbox[0].max}, {middle_y, bbox[1].max}}}, right_mid_it, end);

			geom::vector<float, 2> sum{0.f, 0.f};
			for (int x : {0, 1})
			{
				for (int y : {0, 1})
				{
					auto cid = nodes[id].children[x][y];
					if (cid != node::null)
					{
						nodes[id].mass += nodes[cid].mass;
						sum += (nodes[cid].center - origin) * nodes[cid].mass;
					}
				}
			}

			nodes[id].center = origin + sum / nodes[id].mass;
		}
		else
		{
			nodes[id].mass = 1.f;
			nodes[id].center = *begin;
		}

		return id;
	});

	{
		float max_size = 0.f;
		for (auto const & p : points)
			geom::make_max(max_size, geom::distance(p, origin));

		prof::profiler prof("tree");
		root = add_node(geom::box<float, 2>{{{-max_size, max_size}, {-max_size, max_size}}}, points.begin(), points.end());
	}

	auto force_at = util::recursive([&](auto && self, auto const & p, auto id){
		auto const & n = nodes[id];

		if (n.center == p)
			return geom::vector{0.f, 0.f};

		auto d = p - n.center;

		auto l = geom::length(d);

		if (n.mass == 1.f || l > n.size * multipole_threshold)
			return n.mass * d / std::pow(l, 3.f);

		geom::vector sum{0.f, 0.f};

		for (int x : {0, 1})
		{
			for (int y : {0, 1})
			{
				auto cid = nodes[id].children[x][y];
				if (cid != node::null)
					sum += self(p, cid);
			}
		}

		return sum;
	});

	std::vector<geom::vector<float, 2>> delta;

	for (int iteration = 0; iteration < iterations; ++iteration)
	{
		prof::profiler prof("descent");
		delta.assign(points.size(), geom::vector<float, 2>::zero());

		for (std::size_t i = 0; i < points.size(); ++i)
			delta[i] += 2.f * potential * (origin - points[i]);

		// Exact O(n^2) method
//		for (std::size_t i = 0; i < points.size(); ++i)
//		{
//			for (std::size_t j = i + 1; j < points.size(); ++j)
//			{
//				auto d = points[i] - points[j];

//				d /= std::pow(geom::length(d), 3.f);

//				delta[i] += d;
//				delta[j] -= d;
//			}
//		}

		// Barnes-Hut algorithm
		for (std::size_t i = 0; i < points.size(); ++i)
			delta[i] += force_at(points[i], root);

		for (std::size_t i = 0; i < points.size(); ++i)
			points[i] += delta[i] * step * dt;
	}

	simulation_radius += (simulation_radius_tgt - simulation_radius) * (1.f - std::exp(-10.f * dt));

	prof::profiler prof("delaunay");

	auto const dcel = cg::delaunay<std::uint32_t>(geom::robust, points.begin(), points.end());

	edges.clear();
	degree.assign(points.size(), 0);
	for (std::size_t i = 0; i < dcel.edges.size(); ++i)
	{
		auto const e = dcel.edge(i);
		auto const v0 = e.origin().index();
		auto const v1 = e.twin().origin().index();
		if (v0 < v1)
			edges.push_back({v0, v1});
		degree[v0]++;
	}
}

void main_scene::present()
{
	gl::ClearColor(1.f, 1.f, 1.f, 0.f);
	gl::Clear(gl::COLOR_BUFFER_BIT | gl::DEPTH_BUFFER_BIT);

	geom::box<float, 3> view_area;
	{
		view_area[0] = {-simulation_radius, simulation_radius};
		view_area[1] = {-simulation_radius, simulation_radius};
		view_area[2] = {-1.f, 1.f};

		float const aspect_ratio = width() * 1.f / height();

		float extra_y = view_area[1].length() * 0.1f;
		view_area[1].min -= extra_y;
		view_area[1].max += extra_y;
		float extra_x = view_area[1].length() * aspect_ratio - view_area[0].length();
		view_area[0].min -= extra_x / 2.f;
		view_area[0].max += extra_x / 2.f;
	}

	geom::matrix<float, 4, 4> const transform = geom::orthographic{view_area}.homogeneous_matrix();

	float const pixel_size = view_area[0].length() / width();

	for (auto const & e : edges)
		painter.line(points[e[0]], points[e[1]], 2.f * pixel_size, {127, 127, 127, 255}, false);

	for (std::size_t i = 0; i < points.size(); ++i)
	{
		gfx::color_rgba color{0, 0, 0, 255};
		int quality = 6;
		if (degree[i] == 5)
		{
			quality = 3;
			color = {255, 0, 0, 255};
		}
		else if (degree[i] == 7)
		{
			quality = 4;
			color = {0, 0, 255, 255};
		}
		painter.circle(points[i], 6.f * pixel_size, color, quality);
	}

	painter.render(transform);

	ui_scene::present();
}

struct electron_crystal_app
	: app::app
{
	electron_crystal_app();
	~electron_crystal_app();

	async::event_loop event_loop;
	ui::controller ui_controller;
};

electron_crystal_app::electron_crystal_app()
	: app("Electron crystal simulation", 4)
	, ui_controller(&event_loop)
{
	push_scene(std::make_shared<main_scene>(ui_controller));
}

electron_crystal_app::~electron_crystal_app()
{
	prof::dump();
}

int main()
{
	return app::main<electron_crystal_app>();
}