using System;
using UnityEngine;
using System.Collections;

public class CulledObject : MonoBehaviour
{
    /// <summary>
    /// Defines the render distance between objects, if the object is within this distance then it will render.
    /// </summary>
    public static float RenderDistance = 20;

    private Camera playerCamera;            // the camera linked to the player
    private MeshRenderer mesh;              // the mesh to enable/disable during the distance check

    private bool outOfDistanceLastFrame;    // if we were out of distance in the last Update()

    void Start ()
    {
        // attempt to get the camera controlled by the player
        playerCamera = GameObject.FindGameObjectWithTag ("MainCamera").GetComponent<Camera> ();
        if (playerCamera == null)
            print ("The main camera was not found inside CulledObject script.");

        // attempt to get the meshRenderer component on the culled object
        mesh = GetComponent<MeshRenderer> ();
        if (mesh == null)
            print ("CulledObjects require a mesh component on the same object, in order to enable and disable the object.");
    }

    void Update ()
    {
        // calculates if object is within the camera distances range
        var inRange = InDistanceOfCamera ();

        // if the object is not within the camera range, set out of distance
        if (!inRange)
            OnObjectOutOfDistance ();
        // if the object is in range, is viewed and was out of distance last frame
        else if (ObjectIsViewedByCamera () && outOfDistanceLastFrame)
            OnObjectInDistance ();
        // if the object is: in range, not viewed and was not out of distance last frame
        else if (!ObjectIsViewedByCamera () && !outOfDistanceLastFrame)
            OnObjectOutOfDistance ();
    }

    /// <summary>
    /// Checks if the object is currently viewed by the players camera
    /// </summary>
    bool ObjectIsViewedByCamera ()
    {
        var view = playerCamera.WorldToViewportPoint (transform.position);
        return ((ValueIsClose (view.x)) && (ValueIsClose (view.y)) && (view.z >= 0));
    }

    /// <summary>
    /// Checks if the float is between 0 and 1
    /// </summary>
    /// <param name="val">The value to check.</param>
    /// <returns></returns>
    static bool ValueIsClose (float val)
    {
        return ((val > -1.5) && (val < 1.5));
    }

    /// <summary>
    /// Calculates the distance between the gameObject and the players camera.
    /// </summary>
    /// <returns>Distance between the transform and player.</returns>
    float GetCullDistance ()
    {
        return Math.Abs (Vector3.Distance (transform.position, playerCamera.transform.position));
    }

    /// <summary>
    /// Calls the appropiate events for the object being in or out of distance.
    /// </summary>
    /// <param name="distance"></param>
    bool InDistanceOfCamera ()
    {
        return (GetCullDistance () < RenderDistance);
    }

    /// <summary>
    /// Called when the object is out of the distance of the camera - and it was in distance last frame.
    /// </summary>
    void OnObjectOutOfDistance ()
    {
        outOfDistanceLastFrame = true;

        if (mesh.enabled)
            mesh.enabled = false;
    }

    /// <summary>
    /// Called when the object is in distance of the camera - and it was not in distance last frame.
    /// </summary>
    void OnObjectInDistance ()
    {
        outOfDistanceLastFrame = false;

        if (!mesh.enabled)
            mesh.enabled = true;
    }
}