#include "movementsolver.hpp"

#include <BulletCollision/CollisionDispatch/btCollisionObject.h>
#include <BulletCollision/CollisionDispatch/btCollisionWorld.h>
#include <BulletCollision/CollisionShapes/btConvexShape.h>

#include <components/esm3/loadgmst.hpp>
#include <components/misc/convert.hpp>

#include "../mwbase/environment.hpp"

#include "../mwworld/esmstore.hpp"

#include "actor.hpp"
#include "collisiontype.hpp"
#include "constants.hpp"
#include "contacttestwrapper.h"
#include "object.hpp"
#include "physicssystem.hpp"
#include "projectile.hpp"
#include "projectileconvexcallback.hpp"
#include "stepper.hpp"
#include "trace.h"

#include <cmath>

namespace MWPhysics
{
    static bool isActor(const btCollisionObject* obj)
    {
        assert(obj);
        return obj->getBroadphaseHandle()->m_collisionFilterGroup == CollisionType_Actor;
    }

    namespace
    {
        class ContactCollectionCallback : public btCollisionWorld::ContactResultCallback
        {
        public:
            explicit ContactCollectionCallback(const btCollisionObject& me, const osg::Vec3f& velocity)
                : mVelocity(Misc::Convert::toBullet(velocity))
            {
                m_collisionFilterGroup = me.getBroadphaseHandle()->m_collisionFilterGroup;
                m_collisionFilterMask = me.getBroadphaseHandle()->m_collisionFilterMask & ~CollisionType_Projectile;
            }

            btScalar addSingleResult(btManifoldPoint& contact, const btCollisionObjectWrapper* colObj0Wrap,
                int /*partId0*/, int /*index0*/, const btCollisionObjectWrapper* colObj1Wrap, int /*partId1*/,
                int /*index1*/) override
            {
                if (isActor(colObj0Wrap->getCollisionObject()) && isActor(colObj1Wrap->getCollisionObject()))
                    return 0.0;
                // ignore overlap if we're moving in the same direction as it would push us out (don't change this to
                // >=, that would break detection when not moving)
                if (contact.m_normalWorldOnB.dot(mVelocity) > 0.0)
                    return 0.0;
                auto delta = contact.m_normalWorldOnB * -contact.m_distance1;
                mContactSum += delta;
                mMaxX = std::max(std::abs(delta.x()), mMaxX);
                mMaxY = std::max(std::abs(delta.y()), mMaxY);
                mMaxZ = std::max(std::abs(delta.z()), mMaxZ);
                if (contact.m_distance1 < mDistance)
                {
                    mDistance = contact.m_distance1;
                    mNormal = contact.m_normalWorldOnB;
                    mDelta = delta;
                    return mDistance;
                }
                else
                {
                    return 0.0;
                }
            }

            btScalar mMaxX = 0.0;
            btScalar mMaxY = 0.0;
            btScalar mMaxZ = 0.0;
            btVector3 mContactSum{ 0.0, 0.0, 0.0 };
            btVector3 mNormal{ 0.0, 0.0, 0.0 }; // points towards "me"
            btVector3 mDelta{ 0.0, 0.0, 0.0 }; // points towards "me"
            btScalar mDistance = 0.0; // negative or zero

        protected:
            btVector3 mVelocity;
        };
    }

    osg::Vec3f MovementSolver::traceDown(const MWWorld::Ptr& ptr, const osg::Vec3f& position, Actor* actor,
        btCollisionWorld* collisionWorld, float maxHeight)
    {
        osg::Vec3f offset = actor->getCollisionObjectPosition() - ptr.getRefData().getPosition().asVec3();

        ActorTracer tracer;
        tracer.findGround(actor, position + offset, position + offset - osg::Vec3f(0, 0, maxHeight), collisionWorld);
        if (tracer.mFraction >= 1.0f)
        {
            actor->setOnGround(false);
            return position;
        }

        actor->setOnGround(true);

        // Check if we actually found a valid spawn point (use an infinitely thin ray this time).
        // Required for some broken door destinations in Morrowind.esm, where the spawn point
        // intersects with other geometry if the actor's base is taken into account
        btVector3 from = Misc::Convert::toBullet(position);
        btVector3 to = from - btVector3(0, 0, maxHeight);

        btCollisionWorld::ClosestRayResultCallback resultCallback1(from, to);
        resultCallback1.m_collisionFilterGroup = CollisionType_AnyPhysical;
        resultCallback1.m_collisionFilterMask = CollisionType_World | CollisionType_HeightMap;

        collisionWorld->rayTest(from, to, resultCallback1);

        if (resultCallback1.hasHit()
            && ((Misc::Convert::toOsg(resultCallback1.m_hitPointWorld) - tracer.mEndPos + offset).length2() > 35 * 35
                || !isWalkableSlope(tracer.mPlaneNormal)))
        {
            actor->setOnSlope(!isWalkableSlope(resultCallback1.m_hitNormalWorld));
            return Misc::Convert::toOsg(resultCallback1.m_hitPointWorld) + osg::Vec3f(0.f, 0.f, sGroundOffset);
        }

        actor->setOnSlope(!isWalkableSlope(tracer.mPlaneNormal));

        return tracer.mEndPos - offset + osg::Vec3f(0.f, 0.f, sGroundOffset);
    }

    void MovementSolver::move(
        ActorFrameData& actor, float time, const btCollisionWorld* collisionWorld, const WorldFrameData& worldData)
    {
        // Reset per-frame data
        actor.mWalkingOnWater = false;
        // Anything to collide with?
        if (actor.mSkipCollisionDetection)
        {
            actor.mPosition += (osg::Quat(actor.mRotation.x(), osg::Vec3f(-1, 0, 0))
                                   * osg::Quat(actor.mRotation.y(), osg::Vec3f(0, 0, -1)))
                * actor.mMovement * time;
            return;
        }

        // Adjust for collision mesh offset relative to actor's "location"
        // (doTrace doesn't take local/interior collision shape translation into account, so we have to do it on our
        // own) for compatibility with vanilla assets, we have to derive this from the vertical half extent instead of
        // from internal hull translation if not for this hack, the "correct" collision hull position would be
        // physicActor->getScaledMeshTranslation()
        actor.mPosition.z() += actor.mHalfExtentsZ; // vanilla-accurate

        float swimlevel = actor.mSwimLevel + actor.mHalfExtentsZ;

        ActorTracer tracer;

        osg::Vec3f velocity;

        // Dead and paralyzed actors underwater will float to the surface,
        // if the CharacterController tells us to do so
        if (actor.mMovement.z() > 0 && actor.mInert && actor.mPosition.z() < swimlevel)
        {
            velocity = osg::Vec3f(0, 0, 1) * 25;
        }
        else if (actor.mPosition.z() < swimlevel || actor.mFlying)
        {
            velocity = (osg::Quat(actor.mRotation.x(), osg::Vec3f(-1, 0, 0))
                           * osg::Quat(actor.mRotation.y(), osg::Vec3f(0, 0, -1)))
                * actor.mMovement;
        }
        else
        {
            velocity = (osg::Quat(actor.mRotation.y(), osg::Vec3f(0, 0, -1))) * actor.mMovement;

            if ((velocity.z() > 0.f && actor.mIsOnGround && !actor.mIsOnSlope)
                || (velocity.z() > 0.f && velocity.z() + actor.mInertia.z() <= -velocity.z() && actor.mIsOnSlope))
                actor.mInertia = velocity;
            else if (!actor.mIsOnGround || actor.mIsOnSlope)
                velocity = velocity + actor.mInertia;
        }

        // Now that we have the effective movement vector, apply wind forces to it
        if (worldData.mIsInStorm && velocity.length() > 0)
        {
            const MWWorld::ESMStore& store = *MWBase::Environment::get().getESMStore();
            const float fStromWalkMult = store.get<ESM::GameSetting>().find("fStromWalkMult")->mValue.getFloat();
            const float angleCos = worldData.mStormDirection * velocity / velocity.length();
            velocity *= 1.f + fStromWalkMult * angleCos;
        }

        Stepper stepper(collisionWorld, actor.mCollisionObject);
        osg::Vec3f origVelocity = velocity;
        osg::Vec3f newPosition = actor.mPosition;
        /*
         * A loop to find newPosition using tracer, if successful different from the starting position.
         * nextpos is the local variable used to find potential newPosition, using velocity and remainingTime
         * The initial velocity was set earlier (see above).
         */
        float remainingTime = time;

        int numTimesSlid = 0;
        osg::Vec3f lastSlideNormal(0, 0, 1);
        osg::Vec3f lastSlideNormalFallback(0, 0, 1);
        bool forceGroundTest = false;

        for (int iterations = 0; iterations < sMaxIterations && remainingTime > 0.0001f; ++iterations)
        {
            osg::Vec3f nextpos = newPosition + velocity * remainingTime;
            bool underwater = newPosition.z() < swimlevel;

            // If not able to fly, don't allow to swim up into the air
            if (!actor.mFlying && nextpos.z() > swimlevel && underwater)
            {
                const osg::Vec3f down(0, 0, -1);
                velocity = reject(velocity, down);
                // NOTE: remainingTime is unchanged before the loop continues
                continue; // velocity updated, calculate nextpos again
            }

            if ((newPosition - nextpos).length2() > 0.0001)
            {
                // trace to where character would go if there were no obstructions
                tracer.doTrace(actor.mCollisionObject, newPosition, nextpos, collisionWorld, actor.mIsOnGround);

                // check for obstructions
                if (tracer.mFraction >= 1.0f)
                {
                    newPosition = tracer.mEndPos; // ok to move, so set newPosition
                    break;
                }
            }
            else
            {
                // The current position and next position are nearly the same, so just exit.
                // Note: Bullet can trigger an assert in debug modes if the positions
                // are the same, since that causes it to attempt to normalize a zero
                // length vector (which can also happen with nearly identical vectors, since
                // precision can be lost due to any math Bullet does internally). Since we
                // aren't performing any collision detection, we want to reject the next
                // position, so that we don't slowly move inside another object.
                break;
            }

            bool seenGround = !actor.mFlying && !underwater
                && ((actor.mIsOnGround && !actor.mIsOnSlope) || isWalkableSlope(tracer.mPlaneNormal));

            // We hit something. Check if we can step up.
            float hitHeight = tracer.mHitPoint.z() - tracer.mEndPos.z() + actor.mHalfExtentsZ;
            osg::Vec3f oldPosition = newPosition;
            bool usedStepLogic = false;
            if (!isActor(tracer.mHitObject))
            {
                if (hitHeight < Constants::sStepSizeUp)
                {
                    // Try to step up onto it.
                    // NOTE: this modifies newPosition and velocity on its own if successful
                    usedStepLogic = stepper.step(newPosition, velocity, remainingTime, seenGround, iterations == 0);
                }
                auto* ptrHolder = static_cast<PtrHolder*>(tracer.mHitObject->getUserPointer());
                if (Object* hitObject = dynamic_cast<Object*>(ptrHolder))
                {
                    hitObject->addCollision(
                        actor.mIsPlayer ? ScriptedCollisionType_Player : ScriptedCollisionType_Actor);
                }
            }
            if (usedStepLogic)
            {
                if (actor.mIsAquatic && newPosition.z() + actor.mHalfExtentsZ > actor.mWaterlevel)
                    newPosition = oldPosition;
                else if (!actor.mFlying && actor.mPosition.z() >= swimlevel)
                    forceGroundTest = true;
            }
            else
            {
                // Can't step up, so slide against what we ran into
                remainingTime *= (1.0f - tracer.mFraction);

                auto planeNormal = tracer.mPlaneNormal;
                // need to know the unadjusted normal to handle certain types of seams properly
                const auto origPlaneNormal = planeNormal;

                // If we touched the ground this frame, and whatever we ran into is a wall of some sort,
                // pretend that its collision normal is pointing horizontally
                // (fixes snagging on slightly downward-facing walls, and crawling up the bases of very steep walls
                // because of the collision margin)
                if (seenGround && !isWalkableSlope(planeNormal) && planeNormal.z() != 0)
                {
                    planeNormal.z() = 0;
                    planeNormal.normalize();
                }

                // Move up to what we ran into (with a bit of a collision margin)
                if ((newPosition - tracer.mEndPos).length2() > sCollisionMargin * sCollisionMargin)
                {
                    auto direction = velocity;
                    direction.normalize();
                    newPosition = tracer.mEndPos;
                    newPosition -= direction * sCollisionMargin;
                }

                osg::Vec3f newVelocity = (velocity * planeNormal <= 0.0) ? reject(velocity, planeNormal) : velocity;
                bool usedSeamLogic = false;

                // check for the current and previous collision planes forming an acute angle; slide along the seam if
                // they do for this, we want to use the original plane normal, or else certain types of geometry will
                // snag
                if (numTimesSlid > 0)
                {
                    auto dotA = lastSlideNormal * origPlaneNormal;
                    auto dotB = lastSlideNormalFallback * origPlaneNormal;
                    if (numTimesSlid <= 1) // ignore fallback normal if this is only the first or second slide
                        dotB = 1.0;
                    if (dotA <= 0.0 || dotB <= 0.0)
                    {
                        osg::Vec3f bestNormal = lastSlideNormal;
                        // use previous-to-previous collision plane if it's acute with current plane but actual previous
                        // plane isn't
                        if (dotB < dotA)
                        {
                            bestNormal = lastSlideNormalFallback;
                            lastSlideNormal = lastSlideNormalFallback;
                        }

                        auto constraintVector = bestNormal ^ origPlaneNormal; // cross product
                        if (constraintVector.length2() > 0) // only if it's not zero length
                        {
                            constraintVector.normalize();
                            newVelocity = project(velocity, constraintVector);

                            // version of surface rejection for acute crevices/seams
                            auto averageNormal = bestNormal + origPlaneNormal;
                            averageNormal.normalize();
                            tracer.doTrace(actor.mCollisionObject, newPosition,
                                newPosition + averageNormal * (sCollisionMargin * 2.0), collisionWorld);
                            newPosition = (newPosition + tracer.mEndPos) / 2.0;

                            usedSeamLogic = true;
                        }
                    }
                }
                // otherwise just keep the normal vector rejection

                // move away from the collision plane slightly, if possible
                // this reduces getting stuck in some concave geometry, like the gaps above the railings in some
                // ald'ruhn buildings this is different from the normal collision margin, because the normal collision
                // margin is along the movement path, but this is along the collision normal
                if (!usedSeamLogic)
                {
                    tracer.doTrace(actor.mCollisionObject, newPosition,
                        newPosition + planeNormal * (sCollisionMargin * 2.0), collisionWorld);
                    newPosition = (newPosition + tracer.mEndPos) / 2.0;
                }

                // short circuit if we went backwards, but only if it was mostly horizontal and we're on the ground
                if (seenGround && newVelocity * origVelocity <= 0.0f)
                {
                    auto perpendicular = newVelocity ^ origVelocity;
                    if (perpendicular.length2() > 0.0f)
                    {
                        perpendicular.normalize();
                        if (std::abs(perpendicular.z()) > 0.7071f)
                            break;
                    }
                }

                // Do not allow sliding up steep slopes if there is gravity.
                // The purpose of this is to prevent air control from letting you slide up tall, unwalkable slopes.
                // For that purpose, it is not necessary to do it when trying to slide along acute seams/crevices (i.e.
                // usedSeamLogic) and doing so would actually break air control in some situations where vanilla allows
                // air control. Vanilla actually allows you to slide up slopes as long as you're in the "walking"
                // animation, which can be true even in the air, so allowing this for seams isn't a compatibility break.
                if (newPosition.z() >= swimlevel && !actor.mFlying && !isWalkableSlope(planeNormal) && !usedSeamLogic)
                    newVelocity.z() = std::min(newVelocity.z(), velocity.z());

                numTimesSlid += 1;
                lastSlideNormalFallback = lastSlideNormal;
                lastSlideNormal = origPlaneNormal;
                velocity = newVelocity;
            }
        }

        bool isOnGround = false;
        bool isOnSlope = false;
        if (forceGroundTest || (actor.mInertia.z() <= 0.f && newPosition.z() >= swimlevel))
        {
            osg::Vec3f from = newPosition;
            auto dropDistance = 2 * sGroundOffset + (actor.mIsOnGround ? sStepSizeDown : 0);
            osg::Vec3f to = newPosition - osg::Vec3f(0, 0, dropDistance);
            tracer.doTrace(actor.mCollisionObject, from, to, collisionWorld, actor.mIsOnGround);
            if (tracer.mFraction < 1.0f)
            {
                if (!isActor(tracer.mHitObject))
                {
                    isOnGround = true;
                    isOnSlope = !isWalkableSlope(tracer.mPlaneNormal);
                    actor.mStandingOn = tracer.mHitObject;

                    if (actor.mStandingOn->getBroadphaseHandle()->m_collisionFilterGroup == CollisionType_Water)
                        actor.mWalkingOnWater = true;
                    if (!actor.mFlying && !isOnSlope)
                    {
                        if (tracer.mFraction * dropDistance > sGroundOffset)
                            newPosition.z() = tracer.mEndPos.z() + sGroundOffset;
                        else
                        {
                            newPosition.z() = tracer.mEndPos.z();
                            tracer.doTrace(actor.mCollisionObject, newPosition,
                                newPosition + osg::Vec3f(0, 0, 2 * sGroundOffset), collisionWorld);
                            newPosition = (newPosition + tracer.mEndPos) / 2.0;
                        }
                    }
                }
                else
                {
                    // Vanilla allows actors to float on top of other actors. Do not push them off.
                    if (!actor.mFlying && isWalkableSlope(tracer.mPlaneNormal)
                        && tracer.mEndPos.z() + sGroundOffset <= newPosition.z())
                        newPosition.z() = tracer.mEndPos.z() + sGroundOffset;

                    isOnGround = false;
                }
            }
            // forcibly treat stuck actors as if they're on flat ground because buggy collisions when inside of things
            // can/will break ground detection
            if (actor.mStuckFrames > 0)
            {
                isOnGround = true;
                isOnSlope = false;
            }
        }

        if ((isOnGround && !isOnSlope) || newPosition.z() < swimlevel || actor.mFlying)
            actor.mInertia = osg::Vec3f(0.f, 0.f, 0.f);
        else
        {
            actor.mInertia.z() -= time * Constants::GravityConst * Constants::UnitsPerMeter;
            if (actor.mInertia.z() < 0)
                actor.mInertia.z() *= actor.mSlowFall;
            if (actor.mSlowFall < 1.f)
            {
                actor.mInertia.x() *= actor.mSlowFall;
                actor.mInertia.y() *= actor.mSlowFall;
            }
        }
        actor.mIsOnGround = isOnGround;
        actor.mIsOnSlope = isOnSlope;

        actor.mPosition = newPosition;
        // remove what was added earlier in compensating for doTrace not taking interior transformation into account
        actor.mPosition.z() -= actor.mHalfExtentsZ; // vanilla-accurate
    }

    void MovementSolver::move(ProjectileFrameData& projectile, float time, const btCollisionWorld* collisionWorld)
    {
        btVector3 btFrom = Misc::Convert::toBullet(projectile.mPosition);
        btVector3 btTo = Misc::Convert::toBullet(projectile.mPosition + projectile.mMovement * time);

        if (btFrom == btTo)
            return;

        assert(projectile.mProjectile != nullptr);

        ProjectileConvexCallback resultCallback(
            projectile.mCaster, projectile.mCollisionObject, btFrom, btTo, *projectile.mProjectile);
        resultCallback.m_collisionFilterMask = CollisionType_AnyPhysical;
        resultCallback.m_collisionFilterGroup = CollisionType_Projectile;

        const btQuaternion btrot = btQuaternion::getIdentity();
        btTransform from_(btrot, btFrom);
        btTransform to_(btrot, btTo);

        const btCollisionShape* shape = projectile.mCollisionObject->getCollisionShape();
        assert(shape->isConvex());
        collisionWorld->convexSweepTest(static_cast<const btConvexShape*>(shape), from_, to_, resultCallback);

        projectile.mPosition
            = Misc::Convert::toOsg(projectile.mProjectile->isActive() ? btTo : resultCallback.m_hitPointWorld);
    }

    btVector3 addMarginToDelta(btVector3 delta)
    {
        if (delta.length2() == 0.0)
            return delta;
        return delta + delta.normalized() * sCollisionMargin;
    }

    void MovementSolver::unstuck(ActorFrameData& actor, const btCollisionWorld* collisionWorld)
    {
        if (actor.mSkipCollisionDetection) // noclipping/tcl
            return;

        if (actor.mMovement.length2() == 0) // no AI nor player attempted to move, current position is assumed correct
            return;

        auto tempPosition = actor.mPosition;

        if (actor.mStuckFrames >= 10)
        {
            if ((actor.mLastStuckPosition - actor.mPosition).length2() < 100)
                return;
            else
            {
                actor.mStuckFrames = 0;
                actor.mLastStuckPosition = { 0, 0, 0 };
            }
        }

        // use vanilla-accurate collision hull position hack (do same hitbox offset hack as movement solver)
        // if vanilla compatibility didn't matter, the "correct" collision hull position would be
        // physicActor->getScaledMeshTranslation()
        const auto verticalHalfExtent = osg::Vec3f(0.0, 0.0, actor.mHalfExtentsZ);

        // use a 3d approximation of the movement vector to better judge player intent
        auto velocity = (osg::Quat(actor.mRotation.x(), osg::Vec3f(-1, 0, 0))
                            * osg::Quat(actor.mRotation.y(), osg::Vec3f(0, 0, -1)))
            * actor.mMovement;
        // try to pop outside of the world before doing anything else if we're inside of it
        if (!actor.mIsOnGround || actor.mIsOnSlope)
            velocity += actor.mInertia;

        // because of the internal collision box offset hack, and the fact that we're moving the collision box manually,
        // we need to replicate part of the collision box's transform process from scratch
        osg::Vec3f refPosition = tempPosition + verticalHalfExtent;
        osg::Vec3f goodPosition = refPosition;
        const btTransform oldTransform = actor.mCollisionObject->getWorldTransform();
        btTransform newTransform = oldTransform;

        auto gatherContacts = [&](btVector3 newOffset) -> ContactCollectionCallback {
            goodPosition = refPosition + Misc::Convert::toOsg(addMarginToDelta(newOffset));
            newTransform.setOrigin(Misc::Convert::toBullet(goodPosition));
            actor.mCollisionObject->setWorldTransform(newTransform);

            ContactCollectionCallback callback(*actor.mCollisionObject, velocity);
            ContactTestWrapper::contactTest(
                const_cast<btCollisionWorld*>(collisionWorld), actor.mCollisionObject, callback);
            return callback;
        };

        // check whether we're inside the world with our collision box with manually-derived offset
        auto contactCallback = gatherContacts({ 0.0, 0.0, 0.0 });
        if (contactCallback.mDistance < -sAllowedPenetration)
        {
            ++actor.mStuckFrames;
            actor.mLastStuckPosition = actor.mPosition;
            // we are; try moving it out of the world
            auto positionDelta = contactCallback.mContactSum;
            // limit rejection delta to the largest known individual rejections
            if (std::abs(positionDelta.x()) > contactCallback.mMaxX)
                positionDelta *= contactCallback.mMaxX / std::abs(positionDelta.x());
            if (std::abs(positionDelta.y()) > contactCallback.mMaxY)
                positionDelta *= contactCallback.mMaxY / std::abs(positionDelta.y());
            if (std::abs(positionDelta.z()) > contactCallback.mMaxZ)
                positionDelta *= contactCallback.mMaxZ / std::abs(positionDelta.z());

            auto contactCallback2 = gatherContacts(positionDelta);
            // successfully moved further out from contact (does not have to be in open space, just less inside of
            // things)
            if (contactCallback2.mDistance > contactCallback.mDistance)
                tempPosition = goodPosition - verticalHalfExtent;
            // try again but only upwards (fixes some bad coc floors)
            else
            {
                // upwards-only offset
                auto contactCallback3 = gatherContacts({ 0.0, 0.0, std::abs(positionDelta.z()) });
                // success
                if (contactCallback3.mDistance > contactCallback.mDistance)
                    tempPosition = goodPosition - verticalHalfExtent;
                else
                // try again but fixed distance up
                {
                    auto contactCallback4 = gatherContacts({ 0.0, 0.0, 10.0 });
                    // success
                    if (contactCallback4.mDistance > contactCallback.mDistance)
                        tempPosition = goodPosition - verticalHalfExtent;
                }
            }
        }
        else
        {
            actor.mStuckFrames = 0;
            actor.mLastStuckPosition = { 0, 0, 0 };
        }

        actor.mCollisionObject->setWorldTransform(oldTransform);
        actor.mPosition = tempPosition;
    }
}