using System;
using System.Runtime.InteropServices;
using EasingFunction = System.Func<float, float>;

namespace MoonWorks.Audio
{
	public unsafe class SendableVoice : Voice
	{
		private IReceivableVoice OutputVoice;
		private ReverbEffect ReverbEffect;

		byte* pMatrixCoefficients;

		protected float pan = 0;
		public float Pan
		{
			get => pan;
			internal set
			{
				value = Math.MathHelper.Clamp(value, -1f, 1f);
				if (pan != value)
				{
					pan = value;

					if (pan < -1f)
					{
						pan = -1f;
					}
					if (pan > 1f)
					{
						pan = 1f;
					}

					if (Is3D) { return; }

					SetPanMatrixCoefficients();
					FAudio.FAudioVoice_SetOutputMatrix(
						Handle,
						OutputVoice.Handle,
						SourceChannelCount,
						DestinationChannelCount,
						(nint) pMatrixCoefficients,
						0
					);
				}
			}
		}

		private float reverb;
		public unsafe float Reverb
		{
			get => reverb;
			internal set
			{
				if (ReverbEffect != null)
				{
					value = MathF.Max(0, value);
					if (reverb != value)
					{
						reverb = value;

						float* outputMatrix = (float*) pMatrixCoefficients;
						outputMatrix[0] = reverb;
						if (SourceChannelCount == 2)
						{
							outputMatrix[1] = reverb;
						}

						FAudio.FAudioVoice_SetOutputMatrix(
							Handle,
							ReverbEffect.Handle,
							SourceChannelCount,
							1,
							(nint) pMatrixCoefficients,
							0
						);
					}
				}

				#if DEBUG
				if (ReverbEffect == null)
				{
					Logger.LogWarn("Tried to set reverb value before applying a reverb effect");
				}
				#endif
			}
		}

		public SendableVoice(AudioDevice device, uint sourceChannelCount, uint destinationChannelCount) : base(device, sourceChannelCount, destinationChannelCount)
		{
			OutputVoice = device.MasteringVoice;
			nuint memsize = (nuint) (4 * sourceChannelCount * destinationChannelCount);
			pMatrixCoefficients = (byte*) NativeMemory.AllocZeroed(memsize);
			SetPanMatrixCoefficients();
		}

		public virtual void SetPan(float targetValue)
		{
			Pan = targetValue;
			Device.ClearTweens(this, AudioTweenProperty.Pan);
		}

		public virtual void SetPan(float targetValue, float duration, EasingFunction easingFunction)
		{
			Device.CreateTween(this, AudioTweenProperty.Pan, easingFunction, Pan, targetValue, duration, 0);
		}

		public virtual void SetPan(float targetValue, float delayTime, float duration, EasingFunction easingFunction)
		{
			Device.CreateTween(this, AudioTweenProperty.Pan, easingFunction, Pan, targetValue, duration, delayTime);
		}

		public virtual void SetReverb(float targetValue)
		{
			Reverb = targetValue;
			Device.ClearTweens(this, AudioTweenProperty.Reverb);
		}

		public virtual void SetReverb(float targetValue, float duration, EasingFunction easingFunction)
		{
			Device.CreateTween(this, AudioTweenProperty.Reverb, easingFunction, Volume, targetValue, duration, 0);
		}

		public virtual void SetReverb(float targetValue, float delayTime, float duration, EasingFunction easingFunction)
		{
			Device.CreateTween(this, AudioTweenProperty.Reverb, easingFunction, Volume, targetValue, duration, delayTime);
		}

		public unsafe void SetOutputVoice(IReceivableVoice send)
		{
			FAudio.FAudioSendDescriptor* sendDesc = stackalloc FAudio.FAudioSendDescriptor[1];
			sendDesc[0].Flags = 0;
			sendDesc[0].pOutputVoice = send.Handle;

			var sends = new FAudio.FAudioVoiceSends();
			sends.SendCount = 1;
			sends.pSends = (nint) sendDesc;

			FAudio.FAudioVoice_SetOutputVoices(
				Handle,
				ref sends
			);

			OutputVoice = send;
		}

		public virtual unsafe void SetReverbEffectChain(ReverbEffect reverbEffect)
		{
			var sendDesc = stackalloc FAudio.FAudioSendDescriptor[2];
			sendDesc[0].Flags = 0;
			sendDesc[0].pOutputVoice = OutputVoice.Handle;
			sendDesc[1].Flags = 0;
			sendDesc[1].pOutputVoice = reverbEffect.Handle;

			var sends = new FAudio.FAudioVoiceSends();
			sends.SendCount = 2;
			sends.pSends = (nint) sendDesc;

			FAudio.FAudioVoice_SetOutputVoices(
				Handle,
				ref sends
			);

			ReverbEffect = reverbEffect;
		}

		// Taken from https://github.com/FNA-XNA/FNA/blob/master/src/Audio/SoundEffectInstance.cs
		private unsafe void SetPanMatrixCoefficients()
		{
			/* Two major things to notice:
			 * 1. The spec assumes any speaker count >= 2 has Front Left/Right.
			 * 2. Stereo panning is WAY more complicated than you think.
			 *    The main thing is that hard panning does NOT eliminate an
			 *    entire channel; the two channels are blended on each side.
			 * -flibit
			 */
			float* outputMatrix = (float*) pMatrixCoefficients;
			if (SourceChannelCount == 1)
			{
				if (DestinationChannelCount == 1)
				{
					outputMatrix[0] = 1.0f;
				}
				else
				{
					outputMatrix[0] = (pan > 0.0f) ? (1.0f - pan) : 1.0f;
					outputMatrix[1] = (pan < 0.0f) ? (1.0f + pan) : 1.0f;
				}
			}
			else
			{
				if (DestinationChannelCount == 1)
				{
					outputMatrix[0] = 1.0f;
					outputMatrix[1] = 1.0f;
				}
				else
				{
					if (pan <= 0.0f)
					{
						// Left speaker blends left/right channels
						outputMatrix[0] = 0.5f * pan + 1.0f;
						outputMatrix[1] = 0.5f * -pan;
						// Right speaker gets less of the right channel
						outputMatrix[2] = 0.0f;
						outputMatrix[3] = pan + 1.0f;
					}
					else
					{
						// Left speaker gets less of the left channel
						outputMatrix[0] = -pan + 1.0f;
						outputMatrix[1] = 0.0f;
						// Right speaker blends right/left channels
						outputMatrix[2] = 0.5f * pan;
						outputMatrix[3] = 0.5f * -pan + 1.0f;
					}
				}
			}
		}

		protected override unsafe void Destroy()
		{
			NativeMemory.Free(pMatrixCoefficients);
			base.Destroy();
		}
	}
}