// ----------------------------------------------------------------------------
//
//
// OpenSteer -- Steering Behaviors for Autonomous Characters
//
// Copyright (c) 2002-2003, Sony Computer Entertainment America
// Original author: Craig Reynolds <craig_reynolds@playstation.sony.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//
//
// ----------------------------------------------------------------------------
//
//
// SteerLibraryMixin
//
// This mixin (class with templated superclass) adds the "steering library"
// functionality to a given base class.  SteerLibraryMixin assumes its base
// class supports the Ship interface.
//
// 10-04-04 bk:  put everything into the OpenSteer namespace
// 02-06-03 cwr: create mixin (from "SteerMass")
// 06-03-02 cwr: removed TS dependencies
// 11-21-01 cwr: created
//
//
// ----------------------------------------------------------------------------
module openmelee.steer;

class Steer 
{
    // Constructor: initializes state
    this ()
    {
        // set inital state
        reset ();
    }

    // reset state
    void reset () {
        // initial state of wander behavior
        wanderSide = 0;
        wanderUp = 0;
    }
    
    void update(bzBody rBody) {
        
        m_position = rBody.position;
        m_velocity = rBody.linearVelocity;
    }

    // -------------------------------------------------- steering behaviors

    // Wander behavior
    float wanderSide;
    float wanderUp;

    bzVec2 steerForWander (float dt) {
        // random walk wanderSide and wanderUp between -1 and +1
        float speed = 12 * dt; // maybe this (12) should be an argument?
        wanderSide = scalarRandomWalk (wanderSide, speed, -1, +1);
        wanderUp   = scalarRandomWalk (wanderUp,   speed, -1, +1);

        // return a pure lateral steering vector: (+/-Side) + (+/-Up)
        return (side() * wanderSide) + (up() * wanderUp);
    }

    // Seek behavior
    bzVec2 steerForSeek (bzVec2 target) {
        bzVec2 desiredVelocity = target - m_position;
        return desiredVelocity - m_velocity;
    }

    // Flee behavior
    bzVec2 steerForFlee (bzVec2 target) {
        bzVec2 desiredVelocity = m_position - target;
        return desiredVelocity - m_velocity;
    }

    // xxx proposed, experimental new seek/flee [cwr 9-16-02]
    bzVec2 xxxsteerForFlee (bzVec2 target) {
        bzVec2 offset = m_position - target;
        bzVec2 desiredVelocity = offset.truncateLength (maxSpeed ());
        return desiredVelocity - m_velocity;
    }

    bzVec2 xxxsteerForSeek (bzVec2 target) {
        //  bzVec2 offset = target - position;
        bzVec2 offset = target - m_position;
        bzVec2 desiredVelocity = offset.truncateLength (maxSpeed ()); //xxxnew
        return desiredVelocity - m_velocity;
    }

    // ------------------------------------------------------------------------
    // Obstacle Avoidance behavior
    //
    // Returns a steering force to avoid a given obstacle.  The purely
    // lateral steering force will turn our vehicle towards a silhouette edge
    // of the obstacle.  Avoidance is required when (1) the obstacle
    // intersects the vehicle's current path, (2) it is in front of the
    // vehicle, and (3) is within minTimeToCollision seconds of travel at the
    // vehicle's current velocity.  Returns a zero vector value (bzVec2::zero)
    // when no avoidance is required.
    bzVec2 steerToAvoidObstacle (float minTimeToCollision, Obstacle obstacle) {

        bzVec2 avoidance = obstacle.steerToAvoid (this, minTimeToCollision);
        return avoidance;
    }

    // avoids all obstacles in an ObstacleGroup

    bzVec2 steerToAvoidObstacles (float minTimeToCollision, 
                                  ObstacleGroup obstacles) {

        bzVec2 avoidance;
        PathIntersection nearest, next;
        float minDistanceToCollision = minTimeToCollision * speed();

        next.intersect = false;
        nearest.intersect = false;

        // test all obstacles for intersection with my forward axis,
        // select the one whose point of intersection is nearest
        for (ObstacleIterator o = obstacles.begin(); o != obstacles.end(); o++)
        {
            // xxx this should be a generic call on Obstacle, rather than
            // xxx this code which presumes the obstacle is spherical
            findNextIntersectionWithSphere ((SphericalObstacle)**o, next);

            if ((nearest.intersect == false) ||
                ((next.intersect != false)
                 (next.distance < nearest.distance)))
                nearest = next;
        }

        // when a nearest intersection was found
        if ((nearest.intersect != false)
            (nearest.distance < minDistanceToCollision))
        {
            // show the corridor that was checked for collisions
            annotateAvoidObstacle (minDistanceToCollision);

            // compute avoidance steering force: take offset from obstacle to me,
            // take the component of that which is lateral (perpendicular to my
            // forward direction), set length to maxForce, add a bit of forward
            // component (in capture the flag, we never want to slow down)
            bzVec2 offset = m_position - nearest.obstacle.center;
            avoidance = offset.perpendicularComponent (forward());
            avoidance = avoidance.normalize ();
            avoidance *= maxForce ();
            avoidance += forward() * maxForce () * 0.75;
        }

        return avoidance;
    }

    // ------------------------------------------------------------------------
    // Unaligned collision avoidance behavior: avoid colliding with other
    // nearby vehicles moving in unconstrained directions.  Determine which
    // (if any) other other vehicle we would collide with first, then steers
    // to avoid the site of that potential collision.  Returns a steering
    // force vector, which is zero length if there is no impending collision.

    bzVec2 steerToAvoidNeighbors (float minTimeToCollision, AVGroup others) {

        // first priority is to prevent immediate interpenetration
        bzVec2 separation = steerToAvoidCloseNeighbors (0, others);
        if (separation != bzVec2::zero) return separation;

        // otherwise, go on to consider potential future collisions
        float steer = 0;
        Ship* threat = NULL;

        // Time (in seconds) until the most immediate collision threat found
        // so far.  Initial value is a threshold: don't look more than this
        // many frames into the future.
        float minTime = minTimeToCollision;

        // xxx solely for annotation
        bzVec2 xxxThreatPositionAtNearestApproach;
        bzVec2 xxxOurPositionAtNearestApproach;

        // for each of the other vehicles, determine which (if any)
        // pose the most immediate threat of collision.
        for (AVIterator i = others.begin(); i != others.end(); i++)
        {
            Ship other = **i;
            if (other != this)
            {
                // avoid when future positions are this close (or less)
                float collisionDangerThreshold = radius() * 2;

                // predicted time until nearest approach of "this" and "other"
                float time = predictNearestApproachTime (other);

                // If the time is in the future, sooner than any other
                // threatened collision...
                if ((time >= 0)  (time < minTime))
                {
                    // if the two will be close enough to collide,
                    // make a note of it
                    if (computeNearestApproachPositions (other, time)
                        < collisionDangerThreshold)
                    {
                        minTime = time;
                        threat = other;
                        xxxThreatPositionAtNearestApproach
                            = hisPositionAtNearestApproach;
                        xxxOurPositionAtNearestApproach
                            = ourPositionAtNearestApproach;
                    }
                }
            }
        }

        // if a potential collision was found, compute steering to avoid
        if (threat)
        {
            // parallel: +1, perpendicular: 0, anti-parallel: -1
            float parallelness = forward.dot(threat.forward);
            float angle = 0.707f;

            if (parallelness < -angle)
            {
                // anti-parallel "head on" paths:
                // steer away from future threat position
                bzVec2 offset = xxxThreatPositionAtNearestApproach - m_position;
                float sideDot = offset.dot(side());
                steer = (sideDot > 0) ? -1.0f : 1.0f;
            }
            else
            {
                if (parallelness > angle)
                {
                    // parallel paths: steer away from threat
                    bzVec2 offset = threat.position - m_position;
                    float sideDot = offset.dot(side());
                    steer = (sideDot > 0) ? -1.0f : 1.0f;
                }
                else
                {
                    // perpendicular paths: steer behind threat
                    // (only the slower of the two does this)
                    if (threat.speed() <= speed())
                    {
                        float sideDot = side().dot(threat.velocity);
                        steer = (sideDot > 0) ? -1.0f : 1.0f;
                    }
                }
            }
        }

        return side() * steer;
    }

    // Given two vehicles, based on their current positions and velocities,
    // determine the time until nearest approach
    float predictNearestApproachTime (Ship other) {

        // imagine we are at the origin with no velocity,
        // compute the relative velocity of the other vehicle
        bzVec2 myVelocity = m_velocity;
        bzVec2 otherVelocity = other.velocity;
        bzVec2 relVelocity = otherVelocity - myVelocity;
        float relSpeed = relVelocity.length;

        // for parallel paths, the vehicles will always be at the same distance,
        // so return 0 (aka "now") since "there is no time like the present"
        if (relSpeed == 0) return 0;

        // Now consider the path of the other vehicle in this relative
        // space, a line defined by the relative position and velocity.
        // The distance from the origin (our vehicle) to that line is
        // the nearest approach.

        // Take the unit tangent along the other vehicle's path
        bzVec2 relTangent = relVelocity / relSpeed;

        // find distance from its path to origin (compute offset from
        // other to us, find length of projection onto path)
        bzVec2 relPosition = m_position - other.position;
        float projection = relTangent.dot(relPosition);

        return projection / relSpeed;
    }

    // Given the time until nearest approach (predictNearestApproachTime)
    // determine position of each vehicle at that time, and the distance
    // between them
    float computeNearestApproachPositions (Ship other, float time) {

        bzVec2 myTravel =  forward *  speed * time;
        bzVec2 otherTravel = other.forward * other.speed * time;

        bzVec2 myFinal =  m_position + myTravel;
        bzVec2 otherFinal = other.position + otherTravel;

        // xxx for annotation
        ourPositionAtNearestApproach = myFinal;
        hisPositionAtNearestApproach = otherFinal;

        return bzVec2::distance (myFinal, otherFinal);
    }

        // otherwise return zero
        return bzVec2.zeroVect;
    }

    // ------------------------------------------------------------------------
    // pursuit of another vehicle ( version with ceiling on prediction time)

    bzVec2 steerForPursuit (Ship quarry) {
        return steerForPursuit (quarry, FLT_MAX);
    }

    bzVec2 steerForPursuit (Ship quarry, float maxPredictionTime) {

        // offset from this to quarry, that distance, unit vector toward quarry
        bzVec2 offset = quarry.position - m_position;
        float distance = offset.length ();
        bzVec2 unitOffset = offset / distance;

        // how parallel are the paths of "this" and the quarry
        // (1 means parallel, 0 is pependicular, -1 is anti-parallel)
        float parallelness = forward.dot(quarry.forward());

        // how "forward" is the direction to the quarry
        // (1 means dead ahead, 0 is directly to the side, -1 is straight back)
        float forwardness = forward.dot(unitOffset);

        float directTravelTime = distance / speed;
        int f = intervalComparison (forwardness,  -0.707f, 0.707f);
        int p = intervalComparison (parallelness, -0.707f, 0.707f);

        float timeFactor = 0; // to be filled in below

        // Break the pursuit into nine cases, the cross product of the
        // quarry being [ahead, aside, or behind] us and heading
        // [parallel, perpendicular, or anti-parallel] to us.
        switch (f)
        {
        case +1:
            switch (p)
            {
            case +1:          // ahead, parallel
                timeFactor = 4;
                color = gBlack;
                break;
            case 0:           // ahead, perpendicular
                timeFactor = 1.8f;
                break;
            case -1:          // ahead, anti-parallel
                timeFactor = 0.85f;
                break;
            }
            break;
        case 0:
            switch (p)
            {
            case +1:          // aside, parallel
                timeFactor = 1;
                break;
            case 0:           // aside, perpendicular
                timeFactor = 0.8f;
                break;
            case -1:          // aside, anti-parallel
                timeFactor = 4;
                break;
            }
            break;
        case -1:
            switch (p)
            {
            case +1:          // behind, parallel
                timeFactor = 0.5f;
                break;
            case 0:           // behind, perpendicular
                timeFactor = 2;
                break;
            case -1:          // behind, anti-parallel
                timeFactor = 2;
                break;
            }
            break;
        }

        // estimated time until intercept of quarry
        float et = directTravelTime * timeFactor;

        // xxx experiment, if kept, this limit should be an argument
        float etl = (et > maxPredictionTime) ? maxPredictionTime : et;

        // estimated position of quarry at intercept
        bzVec2 target = quarry.predictFuturePosition (etl);

        return steerForSeek (target);
    }

    // ------------------------------------------------------------------------
    // evasion of another vehicle
    bzVec2 steerForEvasion (Ship menace,  float maxPredictionTime)  {

        // offset from this to menace, that distance, unit vector toward menace
        bzVec2 offset = menace.position - m_position;
        float distance = offset.length;

        float roughTime = distance / menace.speed;
        float predictionTime = ((roughTime > maxPredictionTime) ? maxPredictionTime : roughTime);
        bzVec2 target = menace.predictFuturePosition (predictionTime);

        return steerForFlee (target);
    }


    // ------------------------------------------------------------------------
    // tries to maintain a given speed, returns a maxForce-clipped steering
    // force along the forward/backward axis
    bzVec2 steerForTargetSpeed (float targetSpeed) {
        float mf = maxForce();
        float speedError = targetSpeed - speed ();
        return forward () * clip (speedError, -mf, +mf);
    }


    // ----------------------------------------------------------- utilities
    bool isAhead (bzVec2 target) {return isAhead (target, 0.707f);};
    bool isAside (bzVec2 target) {return isAside (target, 0.707f);};
    bool isBehind (bzVec2 target) {return isBehind (target, -0.707f);};

    bool isAhead (bzVec2 target, float cosThreshold)
    {
        bzVec2 targetDirection = (target - m_position ()).normalize ();
        return forward().dot(targetDirection) > cosThreshold;
    }

    bool isAside (bzVec2 target, float cosThreshold)
    {
        bzVec2 targetDirection = (target - m_position ()).normalize ();
        float dp = forward().dot(targetDirection);
        return (dp < cosThreshold)  (dp > -cosThreshold);
    }

    bool isBehind (bzVec2 target, float cosThreshold)
    {
        bzVec2 targetDirection = (target - m_position).normalize ();
        return forward().dot(targetDirection) < cosThreshold;
    }
    
    private:
    
    bzVec2 m_position;
    bzVec2 m_velocity;
    
}