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

Your use of this SDK or tool is subject to the Oculus SDK License Agreement, available at
https://developer.oculus.com/licenses/oculussdk/

Unless required by applicable law or agreed to in writing, the Utilities SDK distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
ANY KIND, either express or implied. See the License for the specific language governing
permissions and limitations under the License.
************************************************************************************/

using UnityEngine;
using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices;

/// <summary>
/// Plays tactile effects on a tracked VR controller.
/// </summary>
public static class OVRHaptics
{
	public readonly static OVRHapticsChannel[] Channels;
	public readonly static OVRHapticsChannel LeftChannel;
	public readonly static OVRHapticsChannel RightChannel;

	private readonly static OVRHapticsOutput[] m_outputs;

	static OVRHaptics()
	{
		Config.Load();

		m_outputs = new OVRHapticsOutput[]
		{
			new OVRHapticsOutput((uint)OVRPlugin.Controller.LTouch),
			new OVRHapticsOutput((uint)OVRPlugin.Controller.RTouch),
		};

		Channels = new OVRHapticsChannel[]
		{
			LeftChannel = new OVRHapticsChannel(0),
			RightChannel = new OVRHapticsChannel(1),
		};
	}

	/// <summary>
	/// Determines the target format for haptics data on a specific device.
	/// </summary>
	public static class Config
	{
		public static int SampleRateHz { get; private set; }
		public static int SampleSizeInBytes { get; private set; }
		public static int MinimumSafeSamplesQueued { get; private set; }
		public static int MinimumBufferSamplesCount { get; private set; }
		public static int OptimalBufferSamplesCount { get; private set; }
		public static int MaximumBufferSamplesCount { get; private set; }

		static Config()
		{
			Load();
		}

		public static void Load()
		{
			OVRPlugin.HapticsDesc desc = OVRPlugin.GetControllerHapticsDesc((uint)OVRPlugin.Controller.RTouch);

			SampleRateHz = desc.SampleRateHz;
			SampleSizeInBytes = desc.SampleSizeInBytes;
			MinimumSafeSamplesQueued = desc.MinimumSafeSamplesQueued;
			MinimumBufferSamplesCount = desc.MinimumBufferSamplesCount;
			OptimalBufferSamplesCount = desc.OptimalBufferSamplesCount;
			MaximumBufferSamplesCount = desc.MaximumBufferSamplesCount;
		}
	}

	/// <summary>
	/// A track of haptics data that can be mixed or sequenced with another track.
	/// </summary>
	public class OVRHapticsChannel
	{
		private OVRHapticsOutput m_output;

		/// <summary>
		/// Constructs a channel targeting the specified output.
		/// </summary>
		public OVRHapticsChannel(uint outputIndex)
		{
			m_output = m_outputs[outputIndex];
		}

		/// <summary>
		/// Cancels any currently-playing clips and immediatly plays the specified clip instead.
		/// </summary>
		public void Preempt(OVRHapticsClip clip)
		{
			m_output.Preempt(clip);
		}

		/// <summary>
		/// Enqueues the specified clip to play after any currently-playing clips finish.
		/// </summary>
		public void Queue(OVRHapticsClip clip)
		{
			m_output.Queue(clip);
		}

		/// <summary>
		/// Adds the specified clip to play simultaneously to the currently-playing clip(s).
		/// </summary>
		public void Mix(OVRHapticsClip clip)
		{
			m_output.Mix(clip);
		}

		/// <summary>
		/// Cancels any currently-playing clips.
		/// </summary>
		public void Clear()
		{
			m_output.Clear();
		}
	}

	private class OVRHapticsOutput
	{
		private class ClipPlaybackTracker
		{
			public int ReadCount { get; set; }
			public OVRHapticsClip Clip { get; set; }

			public ClipPlaybackTracker(OVRHapticsClip clip)
			{
				Clip = clip;
			}
		}

		private bool m_lowLatencyMode = true;
		private bool m_paddingEnabled = true;
		private int m_prevSamplesQueued = 0;
		private float m_prevSamplesQueuedTime = 0;
		private int m_numPredictionHits = 0;
		private int m_numPredictionMisses = 0;
		private int m_numUnderruns = 0;
		private List<ClipPlaybackTracker> m_pendingClips = new List<ClipPlaybackTracker>();
		private uint m_controller = 0;
		private OVRNativeBuffer m_nativeBuffer = new OVRNativeBuffer(OVRHaptics.Config.MaximumBufferSamplesCount * OVRHaptics.Config.SampleSizeInBytes);
		private OVRHapticsClip m_paddingClip = new OVRHapticsClip();

		public OVRHapticsOutput(uint controller)
		{
#if UNITY_ANDROID
			m_paddingEnabled = false;
#endif
			m_controller = controller;
		}

		/// <summary>
		/// The system calls this each frame to update haptics playback.
		/// </summary>
		public void Process()
		{
			var hapticsState = OVRPlugin.GetControllerHapticsState(m_controller);

			float elapsedTime = Time.realtimeSinceStartup - m_prevSamplesQueuedTime;
			if (m_prevSamplesQueued > 0)
			{
				int expectedSamples = m_prevSamplesQueued - (int)(elapsedTime * OVRHaptics.Config.SampleRateHz + 0.5f);
				if (expectedSamples < 0)
					expectedSamples = 0;

				if ((hapticsState.SamplesQueued - expectedSamples) == 0)
					m_numPredictionHits++;
				else
					m_numPredictionMisses++;

				//Debug.Log(hapticsState.SamplesAvailable + "a " + hapticsState.SamplesQueued + "q " + expectedSamples + "e "
				//+ "Prediction Accuracy: " + m_numPredictionHits / (float)(m_numPredictionMisses + m_numPredictionHits));

				if ((expectedSamples > 0) && (hapticsState.SamplesQueued == 0))
				{
					m_numUnderruns++;
					//Debug.LogError("Samples Underrun (" + m_controller + " #" + m_numUnderruns + ") -"
					//        + " Expected: " + expectedSamples
					//        + " Actual: " + hapticsState.SamplesQueued);
				}

				m_prevSamplesQueued = hapticsState.SamplesQueued;
				m_prevSamplesQueuedTime = Time.realtimeSinceStartup;
			}

			int desiredSamplesCount = OVRHaptics.Config.OptimalBufferSamplesCount;
			if (m_lowLatencyMode)
			{
				float sampleRateMs = 1000.0f / (float)OVRHaptics.Config.SampleRateHz;
				float elapsedMs = elapsedTime * 1000.0f;
				int samplesNeededPerFrame = (int)Mathf.Ceil(elapsedMs / sampleRateMs);
				int lowLatencySamplesCount = OVRHaptics.Config.MinimumSafeSamplesQueued + samplesNeededPerFrame;

				if (lowLatencySamplesCount < desiredSamplesCount)
					desiredSamplesCount = lowLatencySamplesCount;
			}

			if (hapticsState.SamplesQueued > desiredSamplesCount)
				return;

			if (desiredSamplesCount > OVRHaptics.Config.MaximumBufferSamplesCount)
				desiredSamplesCount = OVRHaptics.Config.MaximumBufferSamplesCount;
			if (desiredSamplesCount > hapticsState.SamplesAvailable)
				desiredSamplesCount = hapticsState.SamplesAvailable;

			int acquiredSamplesCount = 0;
			int clipIndex = 0;
			while(acquiredSamplesCount < desiredSamplesCount && clipIndex < m_pendingClips.Count)
			{
				int numSamplesToCopy = desiredSamplesCount - acquiredSamplesCount;
				int remainingSamplesInClip = m_pendingClips[clipIndex].Clip.Count - m_pendingClips[clipIndex].ReadCount;
				if (numSamplesToCopy > remainingSamplesInClip)
					numSamplesToCopy = remainingSamplesInClip;

				if (numSamplesToCopy > 0)
				{
					int numBytes = numSamplesToCopy * OVRHaptics.Config.SampleSizeInBytes;
					int dstOffset = acquiredSamplesCount * OVRHaptics.Config.SampleSizeInBytes;
					int srcOffset = m_pendingClips[clipIndex].ReadCount * OVRHaptics.Config.SampleSizeInBytes;
					Marshal.Copy(m_pendingClips[clipIndex].Clip.Samples, srcOffset, m_nativeBuffer.GetPointer(dstOffset), numBytes);

					m_pendingClips[clipIndex].ReadCount += numSamplesToCopy;
					acquiredSamplesCount += numSamplesToCopy;
				}

				clipIndex++;
			}

			for (int i = m_pendingClips.Count - 1; i >= 0 && m_pendingClips.Count > 0; i--)
			{
				if (m_pendingClips[i].ReadCount >= m_pendingClips[i].Clip.Count)
					m_pendingClips.RemoveAt(i);
			}

			if (m_paddingEnabled)
			{
				int desiredPadding = desiredSamplesCount - (hapticsState.SamplesQueued + acquiredSamplesCount);
				if (desiredPadding < (OVRHaptics.Config.MinimumBufferSamplesCount - acquiredSamplesCount))
					desiredPadding = (OVRHaptics.Config.MinimumBufferSamplesCount - acquiredSamplesCount);
				if (desiredPadding > hapticsState.SamplesAvailable)
					desiredPadding = hapticsState.SamplesAvailable;

				if (desiredPadding > 0)
				{
					int numBytes = desiredPadding * OVRHaptics.Config.SampleSizeInBytes;
					int dstOffset = acquiredSamplesCount * OVRHaptics.Config.SampleSizeInBytes;
					int srcOffset = 0;
					Marshal.Copy(m_paddingClip.Samples, srcOffset, m_nativeBuffer.GetPointer(dstOffset), numBytes);

					acquiredSamplesCount += desiredPadding;
				}
			}

			if (acquiredSamplesCount > 0)
			{
				OVRPlugin.HapticsBuffer hapticsBuffer;
				hapticsBuffer.Samples = m_nativeBuffer.GetPointer();
				hapticsBuffer.SamplesCount = acquiredSamplesCount;

				OVRPlugin.SetControllerHaptics(m_controller, hapticsBuffer);

				hapticsState = OVRPlugin.GetControllerHapticsState(m_controller);
				m_prevSamplesQueued = hapticsState.SamplesQueued;
				m_prevSamplesQueuedTime = Time.realtimeSinceStartup;
			}
		}

		/// <summary>
		/// Immediately plays the specified clip without waiting for any currently-playing clip to finish.
		/// </summary>
		public void Preempt(OVRHapticsClip clip)
		{
			m_pendingClips.Clear();
			m_pendingClips.Add(new ClipPlaybackTracker(clip));
		}

		/// <summary>
		/// Enqueues the specified clip to play after any currently-playing clip finishes.
		/// </summary>
		public void Queue(OVRHapticsClip clip)
		{
			m_pendingClips.Add(new ClipPlaybackTracker(clip));
		}

		/// <summary>
		/// Adds the samples from the specified clip to the ones in the currently-playing clip(s).
		/// </summary>
		public void Mix(OVRHapticsClip clip)
		{
			int numClipsToMix = 0;
			int numSamplesToMix = 0;
			int numSamplesRemaining = clip.Count;

			while (numSamplesRemaining > 0 && numClipsToMix < m_pendingClips.Count)
			{
				int numSamplesRemainingInClip = m_pendingClips[numClipsToMix].Clip.Count - m_pendingClips[numClipsToMix].ReadCount;
				numSamplesRemaining -= numSamplesRemainingInClip;
				numSamplesToMix += numSamplesRemainingInClip;
				numClipsToMix++;
			}

			if (numSamplesRemaining > 0)
			{
				numSamplesToMix += numSamplesRemaining;
				numSamplesRemaining = 0;
			}

			if (numClipsToMix > 0)
			{
				OVRHapticsClip mixClip = new OVRHapticsClip(numSamplesToMix);

				OVRHapticsClip a = clip;
				int aReadCount = 0;

				for (int i = 0; i < numClipsToMix; i++)
				{
					OVRHapticsClip b = m_pendingClips[i].Clip;
					for(int bReadCount = m_pendingClips[i].ReadCount; bReadCount < b.Count; bReadCount++)
					{
						if (OVRHaptics.Config.SampleSizeInBytes == 1)
						{
							byte sample = 0; // TODO support multi-byte samples
							if ((aReadCount < a.Count) && (bReadCount < b.Count))
							{
								sample = (byte)(Mathf.Clamp(a.Samples[aReadCount] + b.Samples[bReadCount], 0, System.Byte.MaxValue)); // TODO support multi-byte samples
								aReadCount++;
							}
							else if (bReadCount < b.Count)
							{
								sample = b.Samples[bReadCount]; // TODO support multi-byte samples
							}

							mixClip.WriteSample(sample); // TODO support multi-byte samples
						}
					}
				}

				while (aReadCount < a.Count)
				{
					if (OVRHaptics.Config.SampleSizeInBytes == 1)
					{
						mixClip.WriteSample(a.Samples[aReadCount]); // TODO support multi-byte samples
					}
					aReadCount++;
				}

				m_pendingClips[0] = new ClipPlaybackTracker(mixClip);
				for (int i = 1; i < numClipsToMix; i++)
				{
					m_pendingClips.RemoveAt(1);
				}
			}
			else
			{
				m_pendingClips.Add(new ClipPlaybackTracker(clip));
			}
		}

		public void Clear()
		{
			m_pendingClips.Clear();
		}
	}

	/// <summary>
	/// The system calls this each frame to update haptics playback.
	/// </summary>
	public static void Process()
	{
		Config.Load();

		for (int i = 0; i < m_outputs.Length; i++)
		{
			m_outputs[i].Process();
		}
	}
}