#include <psemek/ui/impl/move_base.hpp>
#include <psemek/react/join.hpp>
#include <psemek/react/map.hpp>

namespace psemek::ui::impl
{

	namespace
	{

		geom::box<float, 2> compute_child_shape(geom::box<float, 2> const & shape, geom::vector<float, 2> const & offset)
		{
			return shape + offset;
		}

	}

	move_base::move_base()
		: offset_({0.f, 0.f})
		, animation_speed_(0.f)
		, child_size_constraints_(size_constraints::max())
		, size_constraints_(react::join(child_size_constraints_))
		, current_offset_{0.f, 0.f}
	{}

	void move_base::reshape(geom::box<float, 2> const & new_shape)
	{
		single_container::reshape(new_shape);

		if (auto child = this->child())
			child->reshape(compute_child_shape(new_shape, current_offset_));
	}

	react::value<struct size_constraints> move_base::size_constraints() const
	{
		return size_constraints_;
	}

	void move_base::set_child(std::unique_ptr<component> child)
	{
		if (child)
			child_size_constraints_.set(child->size_constraints());
		else
			child_size_constraints_.set(size_constraints::max());
		single_container::set_child(std::move(child));
	}

	std::unique_ptr<component> move_base::release_child()
	{
		child_size_constraints_.set(size_constraints::max());
		return single_container::release_child();
	}

	void move_base::animate(float dt)
	{
		if (*animation_speed_ == 0.f)
		{
			if (current_offset_ != *offset_)
			{
				current_offset_ = *offset_;
				reshape(shape());
			}
		}
		else
		{
			auto factor = - std::expm1(- dt * (*animation_speed_));
			auto new_offset = geom::lerp(current_offset_, *offset_, factor);
			if (geom::length(current_offset_ - new_offset) < 1.f / 16.f)
				new_offset = *offset_;

			if (current_offset_ != *offset_)
			{
				current_offset_ = new_offset;
				reshape(shape());
			}
		}
	}

	void move_base::update(move const & value)
	{
		offset_ = value.offset;
		animation_speed_ = value.animation_speed;
	}

}