//
//  EntityCollisionSystem.cpp
//  libraries/entities/src
//
//  Created by Brad Hefta-Gaub on 9/23/14.
//  Copyright 2013-2014 High Fidelity, Inc.
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//

#include <algorithm>
#include <AbstractAudioInterface.h>
#include <VoxelTree.h>
#include <AvatarData.h>
#include <HeadData.h>
#include <HandData.h>

#include "EntityItem.h"
#include "EntityCollisionSystem.h"
#include "EntityEditPacketSender.h"
#include "EntityTree.h"
#include "EntityTreeElement.h"

const int MAX_COLLISIONS_PER_Entity = 16;

EntityCollisionSystem::EntityCollisionSystem(EntityEditPacketSender* packetSender,
    EntityTree* Entities, VoxelTree* voxels, AbstractAudioInterface* audio,
    AvatarHashMap* avatars) : _collisions(MAX_COLLISIONS_PER_Entity) {
    init(packetSender, Entities, voxels, audio, avatars);
}

void EntityCollisionSystem::init(EntityEditPacketSender* packetSender,
    EntityTree* Entities, VoxelTree* voxels, AbstractAudioInterface* audio,
    AvatarHashMap* avatars) {
    _packetSender = packetSender;
    _entities = Entities;
    _voxels = voxels;
    _audio = audio;
    _avatars = avatars;
}

EntityCollisionSystem::~EntityCollisionSystem() {
}

void EntityCollisionSystem::update() {
    // update all Entities
    if (_entities->tryLockForRead()) {
        QList<EntityItem*>& movingEntities = _entities->getMovingEntities();
        foreach (EntityItem* entity, movingEntities) {
            checkEntity(entity);
        }
        _entities->unlock();
    }
}


void EntityCollisionSystem::checkEntity(EntityItem* entity) {
    updateCollisionWithVoxels(entity);
    updateCollisionWithEntities(entity);
    updateCollisionWithAvatars(entity);
}

void EntityCollisionSystem::emitGlobalEntityCollisionWithVoxel(EntityItem* entity, 
                                            VoxelDetail* voxelDetails, const CollisionInfo& collision) {
    EntityItemID entityItemID = entity->getEntityItemID();
    emit EntityCollisionWithVoxel(entityItemID, *voxelDetails, collision);
}

void EntityCollisionSystem::emitGlobalEntityCollisionWithEntity(EntityItem* entityA, 
                                            EntityItem* entityB, const CollisionInfo& collision) {
                                            
    EntityItemID idA = entityA->getEntityItemID();
    EntityItemID idB = entityB->getEntityItemID();
    emit EntityCollisionWithEntity(idA, idB, collision);
}

void EntityCollisionSystem::updateCollisionWithVoxels(EntityItem* entity) {
    glm::vec3 center = entity->getPosition() * (float)(TREE_SCALE);
    float radius = entity->getRadius() * (float)(TREE_SCALE);
    const float ELASTICITY = 0.4f;
    const float DAMPING = 0.05f;
    CollisionInfo collisionInfo;
    collisionInfo._damping = DAMPING;
    collisionInfo._elasticity = ELASTICITY;
    VoxelDetail* voxelDetails = NULL;
    if (_voxels->findSpherePenetration(center, radius, collisionInfo._penetration, (void**)&voxelDetails)) {

        // findSpherePenetration() only computes the penetration but we also want some other collision info
        // so we compute it ourselves here.  Note that we must multiply scale by TREE_SCALE when feeding 
        // the results to systems outside of this octree reference frame.
        collisionInfo._contactPoint = (float)TREE_SCALE * (entity->getPosition() + entity->getRadius() * glm::normalize(collisionInfo._penetration));
        // let the global script run their collision scripts for Entities if they have them
        emitGlobalEntityCollisionWithVoxel(entity, voxelDetails, collisionInfo);

        // we must scale back down to the octree reference frame before updating the Entity properties
        collisionInfo._penetration /= (float)(TREE_SCALE);
        collisionInfo._contactPoint /= (float)(TREE_SCALE);

        applyHardCollision(entity, collisionInfo);
        delete voxelDetails; // cleanup returned details
    }
}

void EntityCollisionSystem::updateCollisionWithEntities(EntityItem* entityA) {
    glm::vec3 center = entityA->getPosition() * (float)(TREE_SCALE);
    float radius = entityA->getRadius() * (float)(TREE_SCALE);
    glm::vec3 penetration;
    EntityItem* entityB;
    if (_entities->findSpherePenetration(center, radius, penetration, (void**)&entityB, Octree::NoLock)) {
        // NOTE: 'penetration' is the depth that 'entityA' overlaps 'entityB'.  It points from A into B.
        glm::vec3 penetrationInTreeUnits = penetration / (float)(TREE_SCALE);

        // Even if the Entities overlap... when the Entities are already moving appart
        // we don't want to count this as a collision.
        glm::vec3 relativeVelocity = entityA->getVelocity() - entityB->getVelocity();

        bool movingTowardEachOther = glm::dot(relativeVelocity, penetrationInTreeUnits) > 0.0f;
        bool doCollisions = movingTowardEachOther; // don't do collisions if the entities are moving away from each other

        if (doCollisions) {
            quint64 now = usecTimestampNow();
        
            CollisionInfo collision;
            collision._penetration = penetration;
            // for now the contactPoint is the average between the the two paricle centers
            collision._contactPoint = (0.5f * (float)TREE_SCALE) * (entityA->getPosition() + entityB->getPosition());
            emitGlobalEntityCollisionWithEntity(entityA, entityB, collision);

            glm::vec3 axis = glm::normalize(penetration);
            glm::vec3 axialVelocity = glm::dot(relativeVelocity, axis) * axis;

            float massA = entityA->getMass();
            float massB = entityB->getMass();
            float totalMass = massA + massB;

            // handle Entity A
            glm::vec3 newVelocityA = entityA->getVelocity() - axialVelocity * (2.0f * massB / totalMass);
            glm::vec3 newPositionA = entityA->getPosition() - 0.5f * penetrationInTreeUnits;

            EntityItemProperties propertiesA = entityA->getProperties();
            EntityItemID idA(entityA->getID());
            propertiesA.setVelocity(newVelocityA * (float)TREE_SCALE);
            propertiesA.setPosition(newPositionA * (float)TREE_SCALE);
            propertiesA.setLastEdited(now);
            
            _entities->updateEntity(idA, propertiesA);
            _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, idA, propertiesA);

            glm::vec3 newVelocityB = entityB->getVelocity() + axialVelocity * (2.0f * massA / totalMass);
            glm::vec3 newPositionB = entityB->getPosition() + 0.5f * penetrationInTreeUnits;

            EntityItemProperties propertiesB = entityB->getProperties();

            EntityItemID idB(entityB->getID());
            propertiesB.setVelocity(newVelocityB * (float)TREE_SCALE);
            propertiesB.setPosition(newPositionB * (float)TREE_SCALE);
            propertiesB.setLastEdited(now);

            _entities->updateEntity(idB, propertiesB);
            _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, idB, propertiesB);
            
            // TODO: Do we need this?
            //_packetSender->releaseQueuedMessages();
        }
    }
}

void EntityCollisionSystem::updateCollisionWithAvatars(EntityItem* entity) {
    
    // Entities that are in hand, don't collide with avatars
    if (!_avatars) {
        return;
    }

    glm::vec3 center = entity->getPosition() * (float)(TREE_SCALE);
    float radius = entity->getRadius() * (float)(TREE_SCALE);
    const float ELASTICITY = 0.9f;
    const float DAMPING = 0.1f;
    glm::vec3 penetration;

    _collisions.clear();
    foreach (const AvatarSharedPointer& avatarPointer, _avatars->getAvatarHash()) {
        AvatarData* avatar = avatarPointer.data();

        float totalRadius = avatar->getBoundingRadius() + radius;
        glm::vec3 relativePosition = center - avatar->getPosition();
        if (glm::dot(relativePosition, relativePosition) > (totalRadius * totalRadius)) {
            continue;
        }

        if (avatar->findSphereCollisions(center, radius, _collisions)) {
            int numCollisions = _collisions.size();
            for (int i = 0; i < numCollisions; ++i) {
                CollisionInfo* collision = _collisions.getCollision(i);
                collision->_damping = DAMPING;
                collision->_elasticity = ELASTICITY;
    
                collision->_addedVelocity /= (float)(TREE_SCALE);
                glm::vec3 relativeVelocity = collision->_addedVelocity - entity->getVelocity();
    
                if (glm::dot(relativeVelocity, collision->_penetration) <= 0.f) {
                    // only collide when Entity and collision point are moving toward each other
                    // (doing this prevents some "collision snagging" when Entity penetrates the object)
                    collision->_penetration /= (float)(TREE_SCALE);
                    applyHardCollision(entity, *collision);
                }
            }
        }
    }
}

void EntityCollisionSystem::applyHardCollision(EntityItem* entity, const CollisionInfo& collisionInfo) {
    // HALTING_* params are determined using expected acceleration of gravity over some timescale.  
    // This is a HACK for entities that bounce in a 1.0 gravitational field and should eventually be made more universal.
    const float HALTING_ENTITY_PERIOD = 0.0167f;  // ~1/60th of a second
    const float HALTING_ENTITY_SPEED = 9.8 * HALTING_ENTITY_PERIOD / (float)(TREE_SCALE);

    //
    //  Update the entity in response to a hard collision.  Position will be reset exactly
    //  to outside the colliding surface.  Velocity will be modified according to elasticity.
    //
    //  if elasticity = 0.0, collision is inelastic (vel normal to collision is lost)
    //  if elasticity = 1.0, collision is 100% elastic.
    //
    glm::vec3 position = entity->getPosition();
    glm::vec3 velocity = entity->getVelocity();

    const float EPSILON = 0.0f;
    glm::vec3 relativeVelocity = collisionInfo._addedVelocity - velocity;
    float velocityDotPenetration = glm::dot(relativeVelocity, collisionInfo._penetration);
    if (velocityDotPenetration < EPSILON) {
        // entity is moving into collision surface
        //
        // TODO: do something smarter here by comparing the mass of the entity vs that of the other thing 
        // (other's mass could be stored in the Collision Info).  The smaller mass should surrender more 
        // position offset and should slave more to the other's velocity in the static-friction case.
        position -= collisionInfo._penetration;

        if (glm::length(relativeVelocity) < HALTING_ENTITY_SPEED) {
            // static friction kicks in and entities moves with colliding object
            velocity = collisionInfo._addedVelocity;
        } else {
            glm::vec3 direction = glm::normalize(collisionInfo._penetration);
            velocity += glm::dot(relativeVelocity, direction) * (1.0f + collisionInfo._elasticity) * direction;    // dynamic reflection
            velocity += glm::clamp(collisionInfo._damping, 0.0f, 1.0f) * (relativeVelocity - glm::dot(relativeVelocity, direction) * direction);   // dynamic friction
        }
    }

    EntityItemProperties properties = entity->getProperties();
    EntityItemID entityItemID(entity->getID());

    properties.setPosition(position * (float)TREE_SCALE);
    properties.setVelocity(velocity * (float)TREE_SCALE);
    properties.setLastEdited(usecTimestampNow());

    _entities->updateEntity(entityItemID, properties);
    _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, entityItemID, properties);
}