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

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 UnityEngine;
using UnityEngine.Assertions;

namespace OculusSampleFramework
{
	public abstract class TrainCarBase : MonoBehaviour
	{
		private static Vector3 OFFSET = new Vector3(0f, 0.0195f, 0f);
		private const float WHEEL_RADIUS = 0.027f;
		private const float TWO_PI = Mathf.PI * 2.0f;

		[SerializeField] protected Transform _frontWheels = null;
		[SerializeField] protected Transform _rearWheels = null;
		[SerializeField] protected TrainTrack _trainTrack = null;
		[SerializeField] protected Transform[] _individualWheels = null;

		public float Distance { get; protected set; }
		protected float scale = 1.0f;

		private Pose _frontPose = new Pose(), _rearPose = new Pose();

		public float Scale
		{
			get { return scale; }
			set { scale = value; }
		}

		protected virtual void Awake()
		{
			Assert.IsNotNull(_frontWheels);
			Assert.IsNotNull(_rearWheels);
			Assert.IsNotNull(_trainTrack);
			Assert.IsNotNull(_individualWheels);
		}

		public void UpdatePose(float distance, TrainCarBase train, Pose pose)
		{
			// distance could be negative; add track length to it in case that happens
			distance = (train._trainTrack.TrackLength + distance) % train._trainTrack.TrackLength;
			if (distance < 0)
			{
				distance += train._trainTrack.TrackLength;
			}

			var currentSegment = train._trainTrack.GetSegment(distance);
			var distanceInto = distance - currentSegment.StartDistance;

			currentSegment.UpdatePose(distanceInto, pose);
		}

		protected void UpdateCarPosition()
		{
			UpdatePose(Distance + _frontWheels.transform.localPosition.z * scale,
			  this, _frontPose);
			UpdatePose(Distance + _rearWheels.transform.localPosition.z * scale,
			  this, _rearPose);

			var midPoint = 0.5f * (_frontPose.Position + _rearPose.Position);
			var carLookDirection = _frontPose.Position - _rearPose.Position;

			transform.position = midPoint + OFFSET;
			transform.rotation = Quaternion.LookRotation(carLookDirection, transform.up);
			_frontWheels.transform.rotation = _frontPose.Rotation;
			_rearWheels.transform.rotation = _rearPose.Rotation;
		}

		protected void RotateCarWheels()
		{
			// divide by radius to get angle
			float angleOfRot = (Distance / WHEEL_RADIUS) % TWO_PI;

			foreach (var individualWheel in _individualWheels)
			{
				individualWheel.localRotation = Quaternion.AngleAxis(Mathf.Rad2Deg * angleOfRot,
				  Vector3.right);
			}
		}

		public abstract void UpdatePosition();
	}
}