//
//  flockOfFish.js
//  examples
//
//  Philip Rosedale
//  Copyright 2016 High Fidelity, Inc.   
//  Fish smimming around in a space in front of you 
//   
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html


var LIFETIME = 300;   //  Fish live for 5 minutes 
var NUM_FISH = 20;
var TANK_WIDTH = 3.0; 
var TANK_HEIGHT = 1.0;  
var FISH_WIDTH = 0.03;
var FISH_LENGTH = 0.15; 
var MAX_SIGHT_DISTANCE = 0.8;
var MIN_SEPARATION = 0.15;
var AVOIDANCE_FORCE = 0.2;
var COHESION_FORCE = 0.05;
var ALIGNMENT_FORCE = 0.05;
var SWIMMING_FORCE = 0.05;
var SWIMMING_SPEED = 1.5;

var fishLoaded = false; 
var fish = [];

var lowerCorner = { x: 0, y: 0, z: 0 };
var upperCorner = { x: 0, y: 0, z: 0 };

function randomVector(scale) {
    return { x: Math.random() * scale - scale / 2.0, y: Math.random() * scale - scale / 2.0, z: Math.random() * scale - scale / 2.0 };
}

function updateFish(deltaTime) {
    if (!Entities.serversExist() || !Entities.canRez()) {
        return;
    }
    if (!fishLoaded) {
        loadFish(NUM_FISH);
        fishLoaded = true;
        return;
    }

    var averageVelocity = { x: 0, y: 0, z: 0 };
    var averagePosition = { x: 0, y: 0, z: 0 };
    var birdPositionsCounted = 0;
    var birdVelocitiesCounted = 0;

    // First pre-load an array with properties  on all the other fish so our per-fish loop
    // isn't doing it. 
    var flockProperties = [];
    for (var i = 0; i < fish.length; i++) {
        var otherProps = Entities.getEntityProperties(fish[i].entityId, ["position", "velocity", "rotation"]);
        flockProperties.push(otherProps);
    }

    for (var i = 0; i < fish.length; i++) {
        if (fish[i].entityId) {
            // Get only the properties we need, because that is faster
            var properties = flockProperties[i];
            //  If fish has been deleted, bail
            if (properties.id != fish[i].entityId) {
                fish[i].entityId = false;
                return;
            }

            // Store old values so we can check if they have changed enough to update
            var velocity = { x: properties.velocity.x, y: properties.velocity.y, z: properties.velocity.z };
            var position = { x: properties.position.x, y: properties.position.y, z: properties.position.z };
            averageVelocity = { x: 0, y: 0, z: 0 };
            averagePosition = { x: 0, y: 0, z: 0 };

            var othersCounted = 0;
            for (var j = 0; j < fish.length; j++) {
                if (i != j) {
                    // Get only the properties we need, because that is faster
                    var otherProps = flockProperties[j];
                    var separation = Vec3.distance(properties.position, otherProps.position);
                    if (separation < MAX_SIGHT_DISTANCE) {
                        averageVelocity = Vec3.sum(averageVelocity, otherProps.velocity);
                        averagePosition = Vec3.sum(averagePosition, otherProps.position);
                        othersCounted++;
                    }
                    if (separation < MIN_SEPARATION) {
                        var pushAway = Vec3.multiply(Vec3.normalize(Vec3.subtract(properties.position, otherProps.position)), AVOIDANCE_FORCE);
                        velocity = Vec3.sum(velocity, pushAway);
                    }
                }
            }

            if (othersCounted > 0) {
                averageVelocity = Vec3.multiply(averageVelocity, 1.0 / othersCounted);
                averagePosition = Vec3.multiply(averagePosition, 1.0 / othersCounted);
                //  Alignment: Follow group's direction and speed
                velocity = Vec3.mix(velocity, Vec3.multiply(Vec3.normalize(averageVelocity), Vec3.length(velocity)), ALIGNMENT_FORCE);
                // Cohesion: Steer towards center of flock
                var towardCenter = Vec3.subtract(averagePosition, position);
                velocity = Vec3.mix(velocity, Vec3.multiply(Vec3.normalize(towardCenter), Vec3.length(velocity)), COHESION_FORCE);
            }

            //  Try to swim at a constant speed
            velocity = Vec3.mix(velocity, Vec3.multiply(Vec3.normalize(velocity), SWIMMING_SPEED), SWIMMING_FORCE);

            //  Keep fish in their 'tank' 
            if (position.x < lowerCorner.x) {
                position.x = lowerCorner.x; 
                velocity.x *= -1.0;
            } else if (position.x > upperCorner.x) {
                position.x = upperCorner.x; 
                velocity.x *= -1.0;
            }
            if (position.y < lowerCorner.y) {
                position.y = lowerCorner.y; 
                velocity.y *= -1.0;
            } else if (position.y > upperCorner.y) {
                position.y = upperCorner.y; 
                velocity.y *= -1.0;
            } 
            if (position.z < lowerCorner.z) {
                position.z = lowerCorner.z; 
                velocity.z *= -1.0;
            } else if (position.z > upperCorner.z) {
                position.z = upperCorner.z; 
                velocity.z *= -1.0;
            } 

            //  Orient in direction of velocity 
            var rotation = Quat.rotationBetween(Vec3.UNIT_NEG_Z, velocity);
            var VELOCITY_FOLLOW_RATE = 0.30;

            //  Only update properties if they have changed, to save bandwidth
            var MIN_POSITION_CHANGE_FOR_UPDATE = 0.001;
            if (Vec3.distance(properties.position, position) < MIN_POSITION_CHANGE_FOR_UPDATE) {
                Entities.editEntity(fish[i].entityId, { velocity: velocity, rotation: Quat.mix(properties.rotation, rotation, VELOCITY_FOLLOW_RATE) });
            } else {
                Entities.editEntity(fish[i].entityId, { position: position, velocity: velocity, rotation: Quat.slerp(properties.rotation, rotation, VELOCITY_FOLLOW_RATE) });
            }
        }
    }
}

// Connect a call back that happens every frame
Script.update.connect(updateFish);

//  Delete our little friends if script is stopped
Script.scriptEnding.connect(function() {
    for (var i = 0; i < fish.length; i++) {
        Entities.deleteEntity(fish[i].entityId);
    }
});

var STARTING_FRACTION = 0.25; 
function loadFish(howMany) {
  var center = Vec3.sum(MyAvatar.position, Vec3.multiply(Quat.getFront(MyAvatar.orientation), 2 * TANK_WIDTH));
  lowerCorner = { x: center.x - TANK_WIDTH / 2, y: center.y, z: center.z - TANK_WIDTH / 2 };
  upperCorner = { x: center.x + TANK_WIDTH / 2, y: center.y + TANK_HEIGHT, z: center.z + TANK_WIDTH / 2 };
  
  for (var i = 0; i < howMany; i++) {
    var position = { 
        x: lowerCorner.x + (upperCorner.x - lowerCorner.x) / 2.0 + (Math.random() - 0.5) * (upperCorner.x - lowerCorner.x) * STARTING_FRACTION, 
        y: lowerCorner.y + (upperCorner.y - lowerCorner.y) / 2.0 + (Math.random() - 0.5) * (upperCorner.y - lowerCorner.y) * STARTING_FRACTION, 
        z: lowerCorner.z + (upperCorner.z - lowerCorner.x) / 2.0 + (Math.random() - 0.5) * (upperCorner.z - lowerCorner.z) * STARTING_FRACTION
    }; 

    fish.push({
        entityId: Entities.addEntity({
                    type: "Box",
                    position: position,
                    rotation: { x: 0, y: 0, z: 0, w: 1 },
                    dimensions: { x: FISH_WIDTH, y: FISH_WIDTH, z: FISH_LENGTH },
                    velocity: { x: SWIMMING_SPEED, y: SWIMMING_SPEED, z: SWIMMING_SPEED },
                    damping: 0.0,
                    dynamic: false,
                    lifetime: LIFETIME,
                    color: { red: 0, green: 255, blue: 255 }
        })
      });
    }
}