using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARSubsystems;

/// <summary>
/// Visualizes the eye gaze position in face space for an <see cref="ARFace"/>.
/// </summary>
/// <remarks>
/// Face space is the space where the origin is the transform of an <see cref="ARFace"/>.
/// </remarks>
[RequireComponent(typeof(ARFace))]
public class FixationPoint2DVisualizer : MonoBehaviour
{
    [SerializeField]
    GameObject m_GUIFixationReticlePrefab;

    public GameObject fixationReticlePrefab
    {
        get => m_GUIFixationReticlePrefab;
        set => m_GUIFixationReticlePrefab = value;
    }
    GameObject m_FixationReticleGameObject;

    Canvas m_Canvas;
    ARFace m_Face;
    XRFaceSubsystem m_FaceSubsystem;

    void Awake()
    {
        m_Face = GetComponent<ARFace>();
    }

    void CreateEyeGameObjectsIfNecessary()
    {
        var canvas = FindObjectOfType<Canvas>();
        if (m_Face.fixationPoint != null && canvas != null && m_FixationReticleGameObject == null)
        {
            m_FixationReticleGameObject = Instantiate(m_GUIFixationReticlePrefab, canvas.transform);
        }
    }

    void SetVisible(bool visible)
    {   
        if (m_FixationReticleGameObject != null)
            m_FixationReticleGameObject.SetActive(visible);
    }

    void OnEnable()
    {
        var faceManager = FindObjectOfType<ARFaceManager>();
        if (faceManager != null && faceManager.subsystem != null && faceManager.subsystem.SubsystemDescriptor.supportsEyeTracking)
        {
            m_FaceSubsystem = (XRFaceSubsystem)faceManager.subsystem;
            SetVisible((m_Face.trackingState == TrackingState.Tracking) && (ARSession.state > ARSessionState.Ready));
            m_Face.updated += OnUpdated;
        }
        else
        {
            enabled = false;
        }
    }

    void OnDisable()
    {
        m_Face.updated -= OnUpdated;
        SetVisible(false);
    }

    void OnUpdated(ARFaceUpdatedEventArgs eventArgs)
    {
        CreateEyeGameObjectsIfNecessary();
        SetVisible((m_Face.trackingState == TrackingState.Tracking) && (ARSession.state > ARSessionState.Ready));
        UpdateScreenReticle();
    }


    void UpdateScreenReticle()
    {
        var mainCamera = Camera.main;

        var fixationInViewSpace = mainCamera.WorldToViewportPoint(m_Face.fixationPoint.position);
        
        // The camera texture is mirrored so x and y must be changed to match where the fixation point is in relation to the face.
        var mirrorFixationInView = new Vector3(1 - fixationInViewSpace.x, 1 - fixationInViewSpace.y, fixationInViewSpace.z);

        if (m_FixationReticleGameObject != null)
        {
            m_FixationReticleGameObject.GetComponent<RectTransform>().anchoredPosition3D = mainCamera.ViewportToScreenPoint(mirrorFixationInView);
        }
    }

}