/************************************************************************************

Copyright (c) Facebook Technologies, LLC and its affiliates. All rights reserved.  

See SampleFramework license.txt for license terms.  Unless required by applicable law 
or agreed to in writing, the sample code is provided “AS IS” WITHOUT WARRANTIES OR 
CONDITIONS OF ANY KIND, either express or implied.  See the license for specific 
language governing permissions and limitations under the license.

************************************************************************************/

using System.Collections;
using UnityEngine;

namespace OculusSampleFramework
{
	public class PanelHMDFollower : MonoBehaviour
	{
		private const float TOTAL_DURATION = 3.0f;
		private const float HMD_MOVEMENT_THRESHOLD = 0.3f;

		[SerializeField] private float _maxDistance = 0.3f;
		[SerializeField] private float _minDistance = 0.05f;
		[SerializeField] private float _minZDistance = 0.05f;

		private OVRCameraRig _cameraRig;
		private Vector3 _panelInitialPosition = Vector3.zero;
		private Coroutine _coroutine = null;
		private Vector3 _prevPos = Vector3.zero;
		private Vector3 _lastMovedToPos = Vector3.zero;

		private void Awake()
		{
			_cameraRig = FindObjectOfType<OVRCameraRig>();
			_panelInitialPosition = transform.position;
		}

		private void Update()
		{
			var centerEyeAnchorPos = _cameraRig.centerEyeAnchor.position;
			var myPosition = transform.position;
			//Distance from centereye since last time we updated panel position.
			float distanceFromLastMovement = Vector3.Distance(centerEyeAnchorPos, _lastMovedToPos);
			float headMovementSpeed = (_cameraRig.centerEyeAnchor.position - _prevPos).magnitude / Time.deltaTime;
			var currDiffFromCenterEye = transform.position - centerEyeAnchorPos;
			var currDistanceFromCenterEye = currDiffFromCenterEye.magnitude;


			// 1) wait for center eye to stabilize after distance gets too large
			// 2) check if center eye is too close to panel
			// 3) check if depth isn't too close
			if (((distanceFromLastMovement > _maxDistance) || (_minZDistance > currDiffFromCenterEye.z) || (_minDistance > currDistanceFromCenterEye)) &&
				headMovementSpeed < HMD_MOVEMENT_THRESHOLD && _coroutine == null)
			{
				if (_coroutine == null)
				{
					_coroutine = StartCoroutine(LerpToHMD());
				}
			}

			_prevPos = _cameraRig.centerEyeAnchor.position;
		}

		private Vector3 CalculateIdealAnchorPosition()
		{
			return _cameraRig.centerEyeAnchor.position + _panelInitialPosition;
		}

		private IEnumerator LerpToHMD()
		{
			Vector3 newPanelPosition = CalculateIdealAnchorPosition();
			_lastMovedToPos = _cameraRig.centerEyeAnchor.position;
			float startTime = Time.time;
			float endTime = Time.time + TOTAL_DURATION;

			while (Time.time < endTime)
			{
				transform.position =
				  Vector3.Lerp(transform.position, newPanelPosition, (Time.time - startTime) / TOTAL_DURATION);
				yield return null;
			}

			transform.position = newPanelPosition;
			_coroutine = null;
		}
	}
}