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/* Author: Ioan Sucan */

#ifndef OMPL_GEOMETRIC_PLANNERS_SBL_SBL_
#define OMPL_GEOMETRIC_PLANNERS_SBL_SBL_

#include "ompl/geometric/planners/PlannerIncludes.h"
#include "ompl/base/ProjectionEvaluator.h"
#include "ompl/datastructures/Grid.h"
#include "ompl/datastructures/PDF.h"
#include <vector>

namespace ompl
{
    namespace geometric
    {
        /**
           @anchor gSBL
           @par Short description
           SBL is a tree-based motion planner that attempts to grow two
           trees at once: one grows from the starting state and the other
           from the goal state. The tree expansion strategy is the same as for \ref gEST "EST".
           Attempts are made to connect these trees
           at every step of the expansion. If they are connected, a
           solution path is obtained. However, this solution path is not
           certain to be valid (the lazy part of the algorithm) so it is
           checked for validity. If invalid parts are found, they are
           removed from the tree and exploration of the state space
           continues until a solution is found.
           To guide the exploration, an additional grid data
           structure is maintained. Grid cells contain states that
           have been previously visited. When deciding which state to
           use for further expansion, this grid is used;
           least-filled grid cells have most chances of being selected. The
           grid is usually imposed on a projection of the state
           space. This projection needs to be set before using the
           planner (setProjectionEvaluator() function). Connection of states in different trees is
           attempted if they fall in the same grid cell. If no projection is
           set, the planner will attempt to use the default projection
           associated to the state space. An exception is thrown if
           no default projection is available either.
           @par External documentation
           G. Sánchez and J.-C. Latombe, A single-query bi-directional probabilistic roadmap planner with lazy collision
           checking, in <em>The Tenth International Symposium on Robotics Research</em>, pp. 403–417, 2001.
           DOI: [10.1007/3-540-36460-9_27](http://dx.doi.org/10.1007/3-540-36460-9_27)<br>
           [[PDF]](http://www.springerlink.com/content/9843341054386hh6/fulltext.pdf)
        */

        /** \brief Single-Query Bi-Directional Probabilistic Roadmap
           Planner with Lazy Collision Checking */
        class SBL : public base::Planner
        {
        public:
            /** \brief The constructor needs the instance of the space information */
            SBL(const base::SpaceInformationPtr &si);

            ~SBL() override;

            /** \brief Set the projection evaluator. This class is
                able to compute the projection of a given state. */
            void setProjectionEvaluator(const base::ProjectionEvaluatorPtr &projectionEvaluator)
            {
                projectionEvaluator_ = projectionEvaluator;
            }

            /** \brief Set the projection evaluator (select one from
                the ones registered with the state space). */
            void setProjectionEvaluator(const std::string &name)
            {
                projectionEvaluator_ = si_->getStateSpace()->getProjection(name);
            }

            /** \brief Get the projection evaluator. */
            const base::ProjectionEvaluatorPtr &getProjectionEvaluator() const
            {
                return projectionEvaluator_;
            }

            /** \brief Set the range the planner is supposed to use.

                This parameter greatly influences the runtime of the
                algorithm. It represents the maximum length of a
                motion to be added in the tree of motions. */
            void setRange(double distance)
            {
                maxDistance_ = distance;
            }

            /** \brief Get the range the planner is using */
            double getRange() const
            {
                return maxDistance_;
            }

            void setup() override;

            base::PlannerStatus solve(const base::PlannerTerminationCondition &ptc) override;

            void clear() override;

            void getPlannerData(base::PlannerData &data) const override;

        protected:
            struct MotionInfo;

            /** \brief A grid cell */
            typedef Grid<MotionInfo>::Cell GridCell;

            /** \brief A PDF of grid cells */
            typedef PDF<GridCell *> CellPDF;

            /** \brief Representation of a motion */
            class Motion
            {
            public:
                /** \brief Default constructor. Allocates no memory */
                Motion() : root(nullptr), state(nullptr), parent(nullptr), valid(false)
                {
                }

                /** \brief Constructor that allocates storage for a state */
                Motion(const base::SpaceInformationPtr &si)
                  : root(nullptr), state(si->allocState()), parent(nullptr), valid(false)
                {
                }

                /** \brief The root of the tree this motion would get to, if we were to follow parent pointers */
                const base::State *root;

                /** \brief The state this motion leads to */
                base::State *state;

                /** \brief The parent motion -- it contains the state this motion originates at */
                Motion *parent;

                /** \brief Flag indicating whether this motion has been checked for validity. */
                bool valid;

                /** \brief The set of motions descending from the current motion */
                std::vector<Motion *> children;
            };

            /** \brief A struct containing an array of motions and a corresponding PDF element */
            struct MotionInfo
            {
                Motion *operator[](unsigned int i)
                {
                    return motions_[i];
                }
                std::vector<Motion *>::iterator begin()
                {
                    return motions_.begin();
                }
                void erase(std::vector<Motion *>::iterator iter)
                {
                    motions_.erase(iter);
                }
                void push_back(Motion *m)
                {
                    motions_.push_back(m);
                }
                unsigned int size() const
                {
                    return motions_.size();
                }
                bool empty() const
                {
                    return motions_.empty();
                }

                std::vector<Motion *> motions_;
                CellPDF::Element *elem_;
            };

            /** \brief Representation of a search tree. Two instances will be used. One for start and one for goal */
            struct TreeData
            {
                TreeData() : grid(0), size(0)
                {
                }

                /** \brief The grid of motions corresponding to this tree */
                Grid<MotionInfo> grid;

                /** \brief The number of motions (in total) from the tree */
                unsigned int size;

                /** \brief The PDF used for selecting a cell from which to sample a motion */
                CellPDF pdf;
            };

            /** \brief Free the memory allocated by the planner */
            void freeMemory()
            {
                freeGridMotions(tStart_.grid);
                freeGridMotions(tGoal_.grid);
            }

            /** \brief Free the memory used by the motions contained in a grid */
            void freeGridMotions(Grid<MotionInfo> &grid);

            /** \brief Add a motion to a tree */
            void addMotion(TreeData &tree, Motion *motion);

            /** \brief Select a motion from a tree */
            Motion *selectMotion(TreeData &tree);

            /** \brief Remove a motion from a tree */
            void removeMotion(TreeData &tree, Motion *motion);

            /** \brief Since solutions are computed in a lazy fashion,
                once trees are connected, the solution found needs to
                be checked for validity. This function checks whether
                the reverse path from a given motion to a root is
                valid. If this is not the case, invalid motions are removed  */
            bool isPathValid(TreeData &tree, Motion *motion);

            /** \brief Check if a solution can be obtained by connecting two trees using a specified motion */
            bool checkSolution(bool start, TreeData &tree, TreeData &otherTree, Motion *motion,
                               std::vector<Motion *> &solution);

            /** \brief The employed state sampler */
            base::ValidStateSamplerPtr sampler_;

            /** \brief The employed projection evaluator */
            base::ProjectionEvaluatorPtr projectionEvaluator_;

            /** \brief The start tree */
            TreeData tStart_;

            /** \brief The goal tree */
            TreeData tGoal_;

            /** \brief The maximum length of a motion to be added in the tree */
            double maxDistance_;

            /** \brief The random number generator to be used */
            RNG rng_;

            /** \brief The pair of states in each tree connected during planning.  Used for PlannerData computation */
            std::pair<base::State *, base::State *> connectionPoint_;
        };
    }
}

#endif
