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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2022                                                               *
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#ifndef __OPENSPACE_CORE___PATH___H__
#define __OPENSPACE_CORE___PATH___H__

#include <openspace/navigation/pathcurve.h>
#include <openspace/navigation/waypoint.h>
#include <ghoul/misc/dictionary.h>
#include <optional>
#include <vector>

namespace openspace {
    struct CameraPose;
} // namespace openspace

namespace openspace::interaction {

class Path {
public:
    enum class Type {
        AvoidCollision = 0,
        ZoomOutOverview,
        Linear,
        AvoidCollisionWithLookAt // @TODO (2021-08-13, emmbr) This type right now leads
                                 // to rapid rotations, but is useful in specific
                                 // scenarios, e.g. close to surfaces. Later we want to
                                 // remove it, and create a curve type that looks nicely
                                 // at the targets when moving, avoids collisions and
                                 // doesn't introduce sudden large changes in rotation
    };

    Path(Waypoint start, Waypoint end, Type type,
        std::optional<double> duration = std::nullopt);

    Waypoint startPoint() const;
    Waypoint endPoint() const;

    /**
     * Return the total length of the the curve for the path, in meters
     */
    double pathLength() const;

    /**
     * Return a vector of positions corresponding to the control points of the path's
     * spline curve
     */
    std::vector<glm::dvec3> controlPoints() const;

    /**
     * Take a step along the current path, corresponding to the delta time step \p dt, and
     * return the resulting camera pose. The \p speedScale is a factor that will be
     * multiplied with the traversal speed
     */
    CameraPose traversePath(double dt, float speedScale = 1.f);

    /**
     * Function that can be used to permaturely quit a path ,for example when skipping
     * to the end
     */
    void quitPath();

    /**
     * Return the identifer of the node that is the current appropriate anchor node, of
     * the start and end waypoint's reference node. Dtermined based on how far along the
     * path we have traveled
     */
    std::string currentAnchor() const;

    /**
     * Return wether the path has reached its end point or not
     */
    bool hasReachedEnd() const;

    /**
     * Compute the interpolated camera pose at a certain distance along a *linear*
     * path. Note that the linear path is a special case, to avoid risks of precision
     * problems for long paths
     */
    CameraPose linearInterpolatedPose(double distance, double displacement);

    /**
     * Compute the interpolated camera pose at a certain distance along the path
     */
    CameraPose interpolatedPose(double distance) const;

    /**
     * Reset variables used to play back path
     */
    void resetPlaybackVariables();

private:
    /**
     * Interpolate between the paths start and end rotation using the approach that
     * corresponds to the path's curve type. The interpolation parameter \p t is the
     * same as for the position interpolation, i.e. the relative traveled distance
     * along the path, in [0, 1]
     *
     * \param t The interpolation parameter, given as the relative traveled distance
                along the path, in [0, 1]
     */
    glm::dquat interpolateRotation(double t) const;

    /**
     * Compute the interpolated rotation quaternion using an eased SLERP approach
     *
     * \param t The interpolation variable for the rotatation interpolation.
     *          Should be the relative traveled distance, in [0, 1]
     */
    glm::dquat easedSlerpRotation(double t) const;

    /**
     * Compute the interpolated rotation quaternion using a method that is customized
     * for linear paths. The camera will first interpoalte to look at the targetted
     * node, and keep doing so for most of the path. At the end, when within a certain
     * distance from the target, the rotation is interpolated so that the camera ends up
     * in the target pose at the end of the path.
     *
     * \param t The interpolation variable for the rotatation interpolation.
     *          Should be the relative traveled distance, in [0, 1]
     */
    glm::dquat linearPathRotation(double t) const;

    /**
     * Compute the interpolated rotation quaternion using an approach that first
     * interpolates to look at the start node, and then the end node, before
     * interpolating to the end rotation
     *
     * \param t The interpolation variable for the rotatation interpolation.
     *          Should be the relative traveled distance, in [0, 1]
     */
    glm::dquat lookAtTargetsRotation(double t) const;

    /**
     * Evaluate the current traversal speed along the path, based on the currently
     * traveled distance. The final speed will be scaled to match the desired duration
     * for the path (which might have been specified by the user)
     *
     * \param traveledDistance The current distance traveled along the path, in meters
     */
    double speedAlongPath(double traveledDistance) const;

    Waypoint _start;
    Waypoint _end;
    Type _type;

    std::unique_ptr<PathCurve> _curve;

    double _speedFactorFromDuration = 1.0;

    // Playback variables
    double _traveledDistance = 0.0; // Meters
    double _progressedTime = 0.0; // Time since playback started (seconds)
    bool _shouldQuit = false;
    CameraPose _prevPose;
};

/**
 * Create a path based on an instruction given as a dictionary. (See top of cpp file
 * for documentation on keys and values for the dictionary.)
 * If /p forceType is specified, that type will primarily be used as the type for the
 * created path. Secondly, the type will be read from the dictionary, and lastly it will
 * use the default from PathNavigator.
 *
 * \return the created path
 */
Path createPathFromDictionary(const ghoul::Dictionary& dictionary,
    std::optional<Path::Type> forceType = std::nullopt);

} // namespace openspace::interaction

#endif // __OPENSPACE_CORE___PATH___H__