#include <psemek/ui/scroller.hpp>

#include <psemek/geom/contains.hpp>

namespace psemek::ui
{

	std::shared_ptr<element> scroller::set_child(std::shared_ptr<element> c)
	{
		auto old = std::move(child_);
		if (old) old->set_parent(nullptr);

		child_ = std::move(c);
		if (child_) child_->set_parent(this);
		children_[0] = child_.get();

		return old;
	}

	void scroller::set_preferred_direction(direction d)
	{
		preferred_direction_ = d;
	}

	bool scroller::set_horizontal_scroll(bool enabled)
	{
		std::swap(horizontal_, enabled);
		return enabled;
	}

	bool scroller::set_vertical_scroll(bool enabled)
	{
		std::swap(vertical_, enabled);
		return enabled;
	}

	bool scroller::on_event(mouse_move const & e)
	{
		mouse_ = e.position;

		auto pos = geom::cast<float>(e.position);

		if (horizontal_scroll())
		{
			auto box = horizontal_box();
			bool over = geom::contains(box, pos);

			switch (horizontal_state_)
			{
			case state_t::normal:
				if (over)
					horizontal_state_ = state_t::mouseover;
				break;
			case state_t::mouseover:
				if (!over)
					horizontal_state_ = state_t::normal;
				break;
			case state_t::mousedown:
				{
					if (!child_)
						return false;

					auto sc = child_->size_constraints();

					float c = geom::unlerp<float>(box[0], e.position[0]);
					c = geom::clamp(c, {0.f, 1.f});

					shift_tgt_[0] = shape_.box[0].length() / 2.f - c * sc[0].min;
					clamp_shift();
				}
				break;
			}
		}

		if (vertical_scroll())
		{
			auto box = vertical_box();
			bool over = geom::contains(box, pos);

			switch (vertical_state_)
			{
			case state_t::normal:
				if (over)
					vertical_state_ = state_t::mouseover;
				break;
			case state_t::mouseover:
				if (!over)
					vertical_state_ = state_t::normal;
				break;
			case state_t::mousedown:
				{
					if (!child_)
						return false;

					auto sc = child_->size_constraints();

					float c = geom::unlerp<float>(box[1], e.position[1]);
					c = geom::clamp(c, {0.f, 1.f});

					shift_tgt_[1] = shape_.box[1].length() / 2.f - c * sc[1].min;
					clamp_shift();
				}
				break;
			}
		}

		return false;
	}

	bool scroller::on_event(mouse_click const & e)
	{
		if (e.button != mouse_button::left)
			return false;

		bool result = false;

		if (horizontal_scroll())
		{
			switch (horizontal_state_)
			{
			case state_t::normal:
				break;
			case state_t::mouseover:
				if (e.down)
				{
					horizontal_state_ = state_t::mousedown;
					result = true;
				}
				break;
			case state_t::mousedown:
				if (!e.down)
				{
					horizontal_state_ = state_t::mouseover;
					result = true;
				}
				break;
			}
		}

		if (vertical_scroll())
		{
			switch (vertical_state_)
			{
			case state_t::normal:
				break;
			case state_t::mouseover:
				if (e.down)
				{
					vertical_state_ = state_t::mousedown;
					result = true;
				}
				break;
			case state_t::mousedown:
				if (!e.down)
				{
					vertical_state_ = state_t::mouseover;
					result = true;
				}
				break;
			}
		}

		return result;
	}

	bool scroller::on_event(mouse_wheel const & e)
	{
		if (mouse_ && geom::contains(shape_.box, geom::cast<float>(*mouse_)))
		{
			geom::vector<float, 2> delta = {0.f, 0.f};

			auto pos = geom::cast<float>(*mouse_);

			auto vcontains = geom::contains(vertical_box(), pos);
			auto hcontains = geom::contains(horizontal_box(), pos);

			if (vertical_scroll() && horizontal_scroll())
			{
				if (vcontains)
					delta[1] = e.delta;
				else if (hcontains)
					delta[0] = e.delta;
				else if (preferred_direction() == direction::vertical)
					delta[1] = e.delta;
				else
					delta[0] = e.delta;
			}
			else if (vertical_scroll())
			{
				delta[1] = e.delta;
			}
			else if (horizontal_scroll())
			{
				delta[0] = e.delta;
			}

			shift_tgt_ += delta * 50.f;
			clamp_shift();
			post_reshape();
			return true;
		}
		return false;
	}

	void scroller::reshape(geom::box<float, 2> const & bbox)
	{
		shape_.box = bbox;

		auto st = merged_own_style();

		if (child_)
		{
			auto child_constraints = child_->size_constraints();

			auto child_bbox = bbox;

			if (horizontal_scroll())
				child_bbox[1].max -= width() * *st->scale;
			if (vertical_scroll())
				child_bbox[0].max -= width() * *st->scale;

			if (horizontal_scroll())
			{
				horizontal_stick_ |= child_bbox[0].length() > child_constraints[0].min;

				if (horizontal_stick_)
				{
					shift_tgt_[0] = std::min(child_bbox[0].length() - child_constraints[0].min, 0.f);
					shift_[0] = shift_tgt_[0];
				}
				child_bbox[0].min += shift_[0];
				child_bbox[0].max = child_bbox[0].min + child_constraints[0].min;
			}

			if (vertical_scroll())
			{
				vertical_stick_ |= child_bbox[1].length() > child_constraints[1].min;

				if (vertical_stick_)
				{
					shift_tgt_[1] = std::min(child_bbox[1].length() - child_constraints[1].min, 0.f);
					shift_[1] = shift_tgt_[1];
				}
				child_bbox[1].min += shift_[1];
				child_bbox[1].max = child_bbox[1].min + child_constraints[1].min;
			}

			child_->reshape(child_bbox);
		}
	}

	geom::box<float, 2> scroller::size_constraints() const
	{
		geom::box<float, 2> result;
		result[0] = {0.f, std::numeric_limits<float>::infinity()};
		result[1] = {0.f, std::numeric_limits<float>::infinity()};

		if (child_)
		{
			auto child_constraints = child_->size_constraints();

			if (!horizontal_scroll())
				result[0] = child_constraints[0];

			if (!vertical_scroll())
				result[1] = child_constraints[1];
		}

		auto st = merged_own_style();

		if (horizontal_scroll())
			result[1].min = std::max<float>(result[1].min, width() * *st->scale);
		if (vertical_scroll())
			result[0].min = std::max<float>(result[0].min, width() * *st->scale);

		return result;
	}

	void scroller::update(float dt)
	{
		shift_ += (shift_tgt_ - shift_) * std::min(25.f * dt, 1.f);
		post_reshape();
	}

	void scroller::draw(painter & p) const
	{
		auto st = merged_own_style();
		float w = width() * *st->scale;

		auto box = shape_.box;
		if (horizontal_scroll())
			box[1].max -= w;
		if (vertical_scroll())
		box[0].max -= w;

		p.begin_stencil();
		p.draw_rect(box, {0, 0, 0, 255});
		p.commit_stencil();
	}

	void scroller::post_draw(painter & p) const
	{
		p.end_stencil();
	}

	scroller::~scroller()
	{
		release_children();
	}

	float scroller::width() const
	{
		return 0;
	}

	geom::box<float, 2> scroller::visible_range() const
	{
		if (!child_)
			return {{{0.f, 1.f}, {0.f, 1.f}}};

		geom::box<float, 2> result;
		auto c = child_->size_constraints();
		result[0] = {- shift_[0] / c[0].min, (shape_.box[0].length() - shift_[0]) / c[0].min};
		result[1] = {- shift_[1] / c[1].min, (shape_.box[1].length() - shift_[1]) / c[1].min};

		result[0].max = std::min(result[0].max, 1.f);
		result[1].max = std::min(result[1].max, 1.f);

		return result;
	}

	geom::box<float, 2> scroller::horizontal_box() const
	{
		auto box = shape_.box;

		float w = width() * *merged_own_style()->scale;

		box[1].min = box[1].max - w;
		if (vertical_scroll())
			box[0].max -= w;
		return box;
	}

	geom::box<float, 2> scroller::vertical_box() const
	{
		auto box = shape_.box;

		float w = width() * *merged_own_style()->scale;

		box[0].min = box[0].max - w;
		if (horizontal_scroll())
			box[1].max -= w;
		return box;
	}

	void scroller::clamp_shift()
	{
		if (!child_)
			return;

		auto c = child_->size_constraints();

		geom::vector<float, 2> min;
		min[0] = shape_.box[0].length() - c[0].min;
		min[1] = shape_.box[1].length() - c[1].min;

		shift_tgt_[0] = std::max(shift_tgt_[0], min[0]);
		horizontal_stick_ = (shift_tgt_[0] == min[0]) || (min[0] > 0.f);
		shift_tgt_[0] = std::min(shift_tgt_[0], 0.f);

		shift_tgt_[1] = std::max(shift_tgt_[1], min[1]);
		vertical_stick_ = (shift_tgt_[1] == min[1]) || (min[1] > 0.f);
		shift_tgt_[1] = std::min(shift_tgt_[1], 0.f);
	}

}