//***********************************************************
// Filename: BallTeleport.cs
// Author: Moritz Kolvenbach, Marco Fendrich
// Last changes: Thursday, 9th of August 2018
// Content: Teleportation with a thrown ball
//***********************************************************

using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Ball teleport by throwing an instantiated object from the player's hand
/// </summary>
public class BallTeleport : MonoBehaviour, IButton
{
    // general reference classes for access
    private GameObject gameManager;
    private Visualiser renderScript;
    private Teleport teleportScript;
    private ViveNavMesh navMesh;

    // list of points within parabola or line being shown to player as indicator for his teleportation
    protected List<Vector3> projectionPoints;
    // distance in meters between the single points of the optical representation
    protected float pointSpacing;
    // maximum number of points being calculated until parabola is being stopped
    protected int pointCount;

    // prefab to be thrown
    public GameObject ballPrefab;
    // instantiated object while throwing
    private GameObject ballObject;

    // current state of teleportation
    private BallState ballState;

    // additional information needed for calculations; details below
    private Vector3 lastPosition;
    private bool isBallAboveMesh;
    private Vector3 teleportDestination;
    private Vector3 normalVector;

    // reference to controller
    private SteamVR_Controller.Device controller;

    // for rendering only
    protected Vector3 normalisedVelocity = Vector3.down;
    protected Vector3 normalisedHitPoint = Vector3.up;

    void Start()
    {
        // get references for variables declared above
        gameManager = GameObject.FindWithTag("GameController");
        teleportScript = (Teleport)gameManager.GetComponent(typeof(Teleport));
        renderScript = (Visualiser)gameManager.GetComponent(typeof(Visualiser));
        navMesh = (ViveNavMesh)gameManager.GetComponent(typeof(ViveNavMesh));
        projectionPoints = new List<Vector3>(pointCount);
        pointSpacing = renderScript.PointSpacing;
        pointCount = renderScript.PointCount;
    }

    void Update()
    {
        // only running when ball is currently being thrown
        if (ballState != BallState.THROWING) return;
        // calculate a line downwards as preparation to show the current teleport target position
        UpdateProjectionPoints();
        // display the calculated points
        renderScript.updateRendering(isBallAboveMesh, projectionPoints, normalisedHitPoint, Vector3.down * 10.0F);
    }

    /// <summary>
    /// Function being called on press by player; checks the state the teleportation is in and either creates a new ball or
    /// destroys the old one. Teleports if the ball was above a valid destination
    /// </summary>
    /// <param name="controllerObject">gameObject of controller</param>
    /// <param name="controllerIdentificator">ID of controller currently using this function</param>
    public void OnButtonDown(GameObject controllerObject, int controllerIdentificator)
    {
        // if no ball is instantiated, create new one
        if (ballState == BallState.NONE)
        {
            // create ball at controller position
            controller = SteamVR_Controller.Input(controllerIdentificator);
            ballObject = Instantiate(ballPrefab, controllerObject.transform.position, controllerObject.transform.rotation);
            // set the ball to stay static at front of controller
            ballObject.GetComponent<Rigidbody>().isKinematic = true;
            ballObject.transform.SetParent(controllerObject.transform);
            // set ballstate to a ball being held
            ballState = BallState.HELD;
        }
        // if a ball is currently instantied and was thrown, destroy it and teleport if the position was valid
        else if (ballState == BallState.THROWING)
        {
            // check whether the ball was above a valid destination
            navMesh.Linecast(ballObject.transform.position, new Vector3(ballObject.transform.position.x, ballObject.transform.position.y - 5.0f, ballObject.transform.position.z), out isBallAboveMesh, out teleportDestination, out normalVector);
            // if so, teleport there
            if (isBallAboveMesh)
            {
                teleportScript.CallTeleport(teleportDestination);
            }
            // if not, give haptic feedback that input was registered as no other feedback would be given
            else
            {
                // vibrate controller
            }
            // destroy ball, stop rendering, reset ball state
            Destroy(ballObject);
            ballState = BallState.NONE;
            renderScript.enabled = false;
        }
    }

    /// <summary>
    /// Function being called on release of button by player; releases ball if one is currently being held
    /// </summary>
    public void OnButtonUp()
    {
        // check if an instantiated ball is being held
        if (ballState != BallState.HELD) return;
        // if so, decouple from controller
        ballObject.GetComponent<Rigidbody>().isKinematic = false;
        ballObject.transform.SetParent(null);
        // give the ball the controller's speed increased by factor
        ballObject.GetComponent<Rigidbody>().velocity = controller.velocity * 2.0F;
        // set ball state to throwing and start rendering position being targeted
        ballState = BallState.THROWING;
        renderScript.enabled = true;
    }

    /// <summary>
    /// Sample a bunch of points along a line until you hit gnd. At that point, cut off the parabola
    /// Entire calculation is analogue to <see class = "ParabolicTeleport"></see> except with downward velocity
    /// </summary>
    private void UpdateProjectionPoints()
    {
        // turn velocity to work straight down
        normalisedVelocity = transform.TransformDirection(Vector3.down);
        projectionPoints.Clear();
        projectionPoints.Add(ballObject.transform.position);

        Vector3 last = ballObject.transform.position;

        for (int i = 0; i < pointCount; i++)
        {
            Vector3 next = new Vector3(last.x, last.y - pointSpacing, last.z);
            Vector3 castHit;
            Vector3 norm;
            bool endOnNavmesh;
            if (navMesh.Linecast(last, next, out endOnNavmesh, out castHit, out norm))
            {
                projectionPoints.Add(castHit);
                normalisedHitPoint = norm;
                isBallAboveMesh = endOnNavmesh;
                return;
            }
            else
            {
                projectionPoints.Add(next);
            }

            last = next;
        }

        normalisedHitPoint = Vector3.up;
        isBallAboveMesh = false;
    }
}

/// <summary>
/// Represents the player's current use of the ball teleport machanic.
/// </summary>
public enum BallState
{
    // The player is not using teleportation right now
    NONE,
    // The player is holding an instance of the ball prefab
    HELD,
    // The ball is currently flying and therefore "selecting" a destination
    THROWING
}