#include <psemek/app/application_base.hpp>
#include <psemek/app/default_application_factory.hpp>
#include <psemek/gfx/gl.hpp>
#include <psemek/gfx/painter.hpp>
#include <psemek/math/box.hpp>
#include <psemek/math/camera.hpp>
#include <psemek/math/gauss.hpp>
#include <psemek/util/ndarray.hpp>
#include <psemek/random/generator.hpp>
#include <psemek/random/device.hpp>
#include <psemek/random/uniform_sphere.hpp>
#include <psemek/pcg/perlin.hpp>
#include <psemek/prof/profiler.hpp>

using namespace psemek;

static const math::vector x_axis {1.f, 0.f};
static const math::vector y_axis {0.5f, std::sqrt(0.75f)};
static const math::vector z_axis = y_axis - x_axis;
static const int N = 64;

static const float dt = 0.1f;
static const float dx = 1.f;
static float const g = 10.f;
static float const friction = std::pow(0.875f, dt);

math::point<float, 2> to_world(int x, int y)
{
	return math::point{0.f, 0.f} + x_axis * (x - N / 2.f) + y_axis * (y - N / 2.f);
}

math::point<float, 2> to_grid(math::point<float, 2> const & p)
{
	static auto matrix = *math::inverse(math::by_columns(x_axis, y_axis));
	static auto zero = math::point{0.f, 0.f};

	return zero + matrix * (p - zero) + math::vector{N / 2.f, N / 2.f};
}

struct water_2d_hex_app
	: app::application_base
{
	water_2d_hex_app(options const &, context const &);

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

	void on_event(app::resize_event const & event) override;
	void on_event(app::key_event const & event) override;

	void stop() override;

private:
	bool vsync_on_ = true;
	std::function<void(bool)> set_vsync_;

	random::generator rng_{random::device{}};

	float aspect_ratio_ = 1.f;
	math::vector<int, 2> screen_size_;
	math::box<float, 2> view_area_;
	gfx::painter painter_;

	bool paused_ = false;
	float time_ = 0.f;

	bool show_velocity_ = false;

	util::ndarray<float, 2> bed_;
	util::ndarray<float, 2> water_;
	util::ndarray<float, 2> flow_x_; // flow_x(x, y) is (x-1, y) => (x, y)
	util::ndarray<float, 2> flow_y_; // flow_y(x, y) is (x, y-1) => (x, y)
	util::ndarray<float, 2> flow_z_; // flow_z(x, y) is (x, y-1) => (x-1, y)
};

water_2d_hex_app::water_2d_hex_app(options const &, context const & ctx)
	: set_vsync_(ctx.vsync)
{
	set_vsync_(vsync_on_);

	bed_.resize({N + 1, N + 1}, 0.f);
	water_.resize({N + 1, N + 1}, 0.f);
	flow_x_.resize({N + 2, N + 1}, 0.f);
	flow_y_.resize({N + 1, N + 2}, 0.f);
	flow_z_.resize({N + 2, N + 2}, 0.f);

	random::uniform_sphere_vector_distribution<float, 2> d_grad;

	util::ndarray<math::vector<float, 2>, 2> perlin_grad({17, 17});
	for (auto & v : perlin_grad)
		v = d_grad(rng_);

	pcg::perlin<float, 2> noise(std::move(perlin_grad));

	for (int y = 0; y <= N; ++y)
	{
		for (int x = 0; x <= N; ++x)
		{
			auto q = (to_world(x, y) - math::point{0.f, 0.f}) / (1.f * N);
			auto p = q + math::vector{0.5f, 0.5f};

			(void)p;

			// Canyon
			bed_(x, y) = std::max(0.f, 10.f * std::abs(2.f * noise(p) - 1.f) - 1.5f);

			// Islands
			// bed_(x, y) = 5.f * math::smoothstep(math::clamp(math::unlerp({0.45f, 0.55f}, noise(p) - 1.f * math::length(q)), {0.f, 1.f}));

			water_(x, y) = 0.f;
		}
	}
}

void water_2d_hex_app::update()
{
	{
		float y_extent = (N / 2) * y_axis[1];
		view_area_[1] = {- y_extent, y_extent};
		view_area_[0] = {- y_extent * aspect_ratio_, y_extent * aspect_ratio_};
	}

	if (state().mouse_button_down.contains(app::mouse_button::left))
	{
		auto m = math::lerp(view_area_, math::vector{state().mouse[0] * 1.f / screen_size_[0], 1.f - state().mouse[1] * 1.f / screen_size_[1]});
		auto p = to_grid(m);

		int const R = 4;

		for (int dy = -R; dy <= R; ++dy)
		{
			for (int dx = -R; dx <= R; ++dx)
			{
				if (dx + dy < -R || dx + dy > R) continue;

				int mx = std::round(p[0]) + dx;
				int my = std::round(p[1]) + dy;

				if (mx >= 0 && mx <= N && my >= 0 && my <= N)
				{
					auto c = to_world(mx, my);
					water_(mx, my) += 10.f * std::exp(- 0.25f * math::distance_sqr(c, m)) * dt;
				}
			}
		}
	}

	if (paused_)
		return;

	prof::profiler prof("update");

	time_ += dt;

	// Init boundary flows
	for (int i = 0; i <= N / 2; ++i)
		if (bed_(N / 2 - i, i) < 0.5f)
			flow_x_(N / 2 - i, i) = 300.f / N;
			// flow_x_(N / 2 - i, i) = 0*std::pow(std::sin(0.5f * time_) * std::sin(math::pi * (i * 4.f / N)), 5.f) * 300.f / N;

	for (int i = 0; i <= N / 2; ++i)
		if (bed_(N - i, N / 2 + i) < 0.5f)
			flow_x_(N - i + 1, N / 2 + i) = 300.f / N;

	// Update X flows
	for (int y = 0; y <= N; ++y)
		// for (int x = 1; x <= N; ++x)
		for (int x = std::max(1, N / 2 + 1 - y); x <= std::min(N, 3 * N / 2 - y); ++x)
			// if (x + y - 1 >= N / 2 && x + y <= 3 * N / 2)
				flow_x_(x, y) = friction * flow_x_(x, y) + g * dt * (water_(x - 1, y) + bed_(x - 1, y) - water_(x, y) - bed_(x, y));

	// Update Y flows
	for (int y = 1; y <= N; ++y)
		// for (int x = 0; x <= N; ++x)
		for (int x = std::max(0, N / 2 + 1 - y); x <= std::min(N, 3 * N / 2 - y); ++x)
			// if (x + y - 1 >= N / 2 && x + y <= 3 * N / 2)
				flow_y_(x, y) = friction * flow_y_(x, y) + g * dt * (water_(x, y - 1) + bed_(x, y - 1) - water_(x, y) - bed_(x, y));

	// Update Z flows
	for (int y = 1; y <= N; ++y)
		// for (int x = 1; x <= N; ++x)
		for (int x = std::max(1, N / 2 + 1 - y); x <= std::min(N, 3 * N / 2 + 1 - y); ++x)
			// if (x + y - 1 >= N / 2 && x + y - 1 <= 3 * N / 2)
				flow_z_(x, y) = friction * flow_z_(x, y) + g * dt * (water_(x, y - 1) + bed_(x, y - 1) - water_(x - 1, y) - bed_(x - 1, y));

	// Scale flows
	for (int y = 0; y <= N; ++y)
	{
		// for (int x = 0; x <= N; ++x)
		for (int x = std::max(0, N / 2 - y); x <= std::min(N, 3 * N / 2 - y); ++x)
		{
			// if (x + y >= N / 2 && x + y <= 3 * N / 2)
			{
				float outflow = 0.f;

				float &  fin1 = flow_x_(x    , y    );
				float &  fin2 = flow_y_(x    , y    );
				float &  fin3 = flow_z_(x + 1, y    );

				float & fout1 = flow_x_(x + 1, y    );
				float & fout2 = flow_y_(x    , y + 1);
				float & fout3 = flow_z_(x    , y + 1);

				outflow += std::max(0.f, -fin1);
				outflow += std::max(0.f, -fin2);
				outflow += std::max(0.f, -fin3);
				outflow += std::max(0.f, fout1);
				outflow += std::max(0.f, fout2);
				outflow += std::max(0.f, fout3);

				if (outflow > 0.f)
				{
					float max_outflow = water_(x, y) * dx * dx / dt;

					float scale = std::min(1.f, max_outflow / outflow);

					fin1 *= (fin1 < 0.f ? scale : 1.f);
					fin2 *= (fin2 < 0.f ? scale : 1.f);
					fin3 *= (fin3 < 0.f ? scale : 1.f);

					fout1 *= (fout1 > 0.f ? scale : 1.f);
					fout2 *= (fout2 > 0.f ? scale : 1.f);
					fout3 *= (fout3 > 0.f ? scale : 1.f);
				}
			}
		}
	}

	// Update water
	for (int y = 0; y <= N; ++y)
		// for (int x = 0; x <= N; ++x)
		for (int x = std::max(0, N / 2 - y); x <= std::min(N, 3 * N / 2 - y); ++x)
			// if (x + y >= N / 2 && x + y <= 3 * N / 2)
				water_(x, y) += dt / dx / dx * (flow_x_(x, y) + flow_y_(x, y) + flow_z_(x + 1,y) - flow_x_(x + 1, y) - flow_y_(x, y + 1) - flow_z_(x, y + 1));
}

void water_2d_hex_app::present()
{
	gl::ClearColor(0.f, 0.f, 0.f, 0.f);
	gl::Clear(gl::COLOR_BUFFER_BIT);

	for (int y = 0; y < N; ++y)
	{
		for (int x = 0; x < N; ++x)
		{
			auto color = [this](int x, int y)
			{
				auto bed = gfx::color_4f{0.9f, 0.7f, 0.5f, - std::expm1(- bed_(x, y))};
				auto water = gfx::color_4f{0.0f, 0.25f, 1.f, - std::expm1(- water_(x, y))};

				auto color = gfx::color_4f{0.f, 0.f, 0.f, 0.f};
				color = gfx::blend(color, bed);
				color = gfx::blend(color, water);
				return gfx::to_coloru8(color);
			};

			auto p00 = to_world(x, y);
			auto p01 = to_world(x + 1, y);
			auto p10 = to_world(x, y + 1);
			auto p11 = to_world(x + 1, y + 1);

			auto b00 = color(x, y);
			auto b01 = color(x + 1, y);
			auto b10 = color(x, y + 1);
			auto b11 = color(x + 1, y + 1);

			if (x + y >= N / 2 && x + y < (3 * N) / 2)
				painter_.triangle(p00, p01, p10, b00, b01, b10);

			if (x + y + 1 >= N / 2 && x + y + 1 < (3 * N) / 2)
				painter_.triangle(p10, p01, p11, b10, b01, b11);
		}
	}

	if (show_velocity_)
	for (int y = 0; y <= N; ++y)
	{
		for (int x = 0; x <= N; ++x)
		{
			if (x + y >= N / 2 && x + y <= (3 * N) / 2)
			{
				auto p = to_world(x, y);

				auto vx = (flow_x_(x, y) + flow_x_(x + 1, y)) * 0.5f * x_axis;
				auto vy = (flow_y_(x, y) + flow_y_(x, y + 1)) * 0.5f * y_axis;
				auto vz = (flow_z_(x + 1, y) + flow_z_(x, y + 1)) * 0.5f * z_axis;

				auto v = (vx + vy + vz);

				auto M = 1.f;
				auto l = math::length(v);
				float s = std::min(1.f, l / M);
				float c = -std::expm1(- 0.1f * l);

				auto color = gfx::to_coloru8(gfx::color_4f{1.f, 1.f - c, 1.f - c, 1.f});

				painter_.line(p, p + v * (s / l), 0.25f * s, 0.f, color, color, true);
			}
		}
	}

	painter_.render(math::orthographic_camera{view_area_}.transform());
}

void water_2d_hex_app::on_event(app::resize_event const & event)
{
	gl::Viewport(0, 0, event.size[0], event.size[1]);
	screen_size_ = event.size;
	aspect_ratio_ = (event.size[0] * 1.f) / event.size[1];
}

void water_2d_hex_app::on_event(app::key_event const & event)
{
	if (event.down)
	{
		switch (event.key)
		{
		case app::keycode::V:
			vsync_on_ ^= true;
			set_vsync_(vsync_on_);
			break;
		case app::keycode::C:
			show_velocity_ ^= true;
			break;
		case app::keycode::SPACE:
			paused_ ^= true;
			break;
		default:
			break;
		}
	}
}


void water_2d_hex_app::stop()
{
	app::application_base::stop();
	prof::dump();
}

namespace psemek::app
{

	std::unique_ptr<application::factory> make_application_factory()
	{
		return default_application_factory<water_2d_hex_app>({.name = "Water 2D hex example", .multisampling = 4});
	}

}