using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.XR.ARFoundation;

/// <summary>
/// A component that can be used to access the most
/// recently received light estimation information
/// for the physical environment as observed by an
/// AR device.
/// </summary>
[RequireComponent(typeof(Light))]
public class LightEstimation : MonoBehaviour
{
    [SerializeField]
    [Tooltip("The ARCameraManager which will produce frame events containing light estimation information.")]
    ARCameraManager m_CameraManager;

    [SerializeField]
    Transform m_Arrow;

    public Transform arrow
    {
        get => m_Arrow;
        set => m_Arrow = value;
    }

    /// <summary>
    /// Get or set the <c>ARCameraManager</c>.
    /// </summary>
    public ARCameraManager cameraManager
    {
        get { return m_CameraManager; }
        set
        {
            if (m_CameraManager == value)
                return;

            if (m_CameraManager != null)
                m_CameraManager.frameReceived -= FrameChanged;

            m_CameraManager = value;

            if (m_CameraManager != null & enabled)
                m_CameraManager.frameReceived += FrameChanged;
        }
    }

    /// <summary>
    /// The estimated brightness of the physical environment, if available.
    /// </summary>
    public float? brightness { get; private set; }

    /// <summary>
    /// The estimated color temperature of the physical environment, if available.
    /// </summary>
    public float? colorTemperature { get; private set; }

    /// <summary>
    /// The estimated color correction value of the physical environment, if available.
    /// </summary>
    public Color? colorCorrection { get; private set; }

    /// <summary>
    /// The estimated direction of the main light of the physical environment, if available.
    /// </summary>
    public Vector3? mainLightDirection { get; private set; }

    /// <summary>
    /// The estimated color of the main light of the physical environment, if available.
    /// </summary>
    public Color? mainLightColor { get; private set; }

    /// <summary>
    /// The estimated intensity in lumens of main light of the physical environment, if available.
    /// </summary>
    public float? mainLightIntensityLumens { get; private set; }

    /// <summary>
    /// The estimated spherical harmonics coefficients of the physical environment, if available.
    /// </summary>
    public SphericalHarmonicsL2? sphericalHarmonics { get; private set; }

    void Awake ()
    {
        m_Light = GetComponent<Light>();
    }

    void OnEnable()
    {
        if (m_CameraManager != null)
            m_CameraManager.frameReceived += FrameChanged;

        // Disable the arrow to start; enable it later if we get directional light info
        arrow?.gameObject.SetActive(false);
        Application.onBeforeRender += OnBeforeRender;
    }

    void OnDisable()
    {
        Application.onBeforeRender -= OnBeforeRender;

        if (m_CameraManager != null)
            m_CameraManager.frameReceived -= FrameChanged;
    }

    void OnBeforeRender()
    {
        if (arrow && m_CameraManager)
        {
            var cameraTransform = m_CameraManager.GetComponent<Camera>().transform;
            arrow.position = cameraTransform.position + cameraTransform.forward * .25f;
        }
    }

    void FrameChanged(ARCameraFrameEventArgs args)
    {
        if (args.lightEstimation.averageBrightness.HasValue)
        {
            brightness = args.lightEstimation.averageBrightness.Value;
            m_Light.intensity = brightness.Value;
        }

        if (args.lightEstimation.averageColorTemperature.HasValue)
        {
            colorTemperature = args.lightEstimation.averageColorTemperature.Value;
            m_Light.colorTemperature = colorTemperature.Value;
        }

        if (args.lightEstimation.colorCorrection.HasValue)
        {
            colorCorrection = args.lightEstimation.colorCorrection.Value;
            m_Light.color = colorCorrection.Value;
        }

        if (args.lightEstimation.mainLightDirection.HasValue)
        {
            mainLightDirection = args.lightEstimation.mainLightDirection;
            m_Light.transform.rotation = Quaternion.LookRotation(mainLightDirection.Value);
            if (arrow)
            {
                arrow.gameObject.SetActive(true);
                arrow.rotation = Quaternion.LookRotation(mainLightDirection.Value);
            }
        }
        else
        {
            arrow?.gameObject.SetActive(false);
        }

        if (args.lightEstimation.mainLightColor.HasValue)
        {
            mainLightColor = args.lightEstimation.mainLightColor;

#if PLATFORM_ANDROID
            // ARCore needs to apply energy conservation term (1 / PI) and be placed in gamma
            m_Light.color = mainLightColor.Value / Mathf.PI;
            m_Light.color = m_Light.color.gamma;

            // ARCore returns color in HDR format (can be represented as FP16 and have values above 1.0)
            var camera = m_CameraManager.GetComponentInParent<Camera>();
            if (camera == null || !camera.allowHDR)
            {
                Debug.LogWarning($"HDR Rendering is not allowed.  Color values returned could be above the maximum representable value.");
            }
#endif
        }

        if (args.lightEstimation.mainLightIntensityLumens.HasValue)
        {
            mainLightIntensityLumens = args.lightEstimation.mainLightIntensityLumens;
            m_Light.intensity = args.lightEstimation.averageMainLightBrightness.Value;
        }

        if (args.lightEstimation.ambientSphericalHarmonics.HasValue)
        {
            sphericalHarmonics = args.lightEstimation.ambientSphericalHarmonics;
            RenderSettings.ambientMode = AmbientMode.Skybox;
            RenderSettings.ambientProbe = sphericalHarmonics.Value;
        }
    }

    Light m_Light;
}