using System;
using System.Runtime.InteropServices;

namespace Nerfed.Runtime.Audio;

/// <summary>
/// Use in conjunction with an AudioDataStreamable object to play back streaming audio data.
/// </summary>
public class StreamingVoice : UpdatingSourceVoice, IPoolable<StreamingVoice>
{
	private const int BUFFER_COUNT = 3;
	private readonly IntPtr[] buffers;
	private int nextBufferIndex = 0;
	private uint BufferSize;

	public bool Loop { get; set; }

	public AudioDataStreamable AudioData { get; protected set; }

	public unsafe StreamingVoice(AudioDevice device, Format format) : base(device, format)
	{
		buffers = new IntPtr[BUFFER_COUNT];
	}

	public static StreamingVoice Create(AudioDevice device, Format format)
	{
		return new StreamingVoice(device, format);
	}

	/// <summary>
	/// Loads and prepares an AudioDataStreamable for streaming playback.
	/// This automatically calls Load on the given AudioDataStreamable.
	/// </summary>
	public void Load(AudioDataStreamable data)
	{
		lock (StateLock)
		{
			if (AudioData != null)
			{
				AudioData.Unload();
			}

			data.Load();
			AudioData = data;

			InitializeBuffers();
			QueueBuffers();
		}
	}

	/// <summary>
	/// Unloads AudioDataStreamable from this voice.
	/// This automatically calls Unload on the given AudioDataStreamable.
	/// </summary>
	public void Unload()
	{
		lock (StateLock)
		{
			if (AudioData != null)
			{
				Stop();
				AudioData.Unload();
				AudioData = null;
			}
		}
	}

	public override void Reset()
	{
		Unload();
		base.Reset();
	}

	public override void Update()
	{
		lock (StateLock)
		{
			if (AudioData == null || State != SoundState.Playing)
			{
				return;
			}

			QueueBuffers();
		}
	}

	private void QueueBuffers()
	{
		int buffersNeeded = BUFFER_COUNT - (int) BuffersQueued; // don't get got by uint underflow!
		for (int i = 0; i < buffersNeeded; i += 1)
		{
			AddBuffer();
		}
	}

	private unsafe void AddBuffer()
	{
		IntPtr buffer = buffers[nextBufferIndex];
		nextBufferIndex = (nextBufferIndex + 1) % BUFFER_COUNT;

		AudioData.Decode(
			(void*) buffer,
			(int) BufferSize,
			out int filledLengthInBytes,
			out bool reachedEnd
		);

		if (filledLengthInBytes > 0)
		{
			FAudio.FAudioBuffer buf = new FAudio.FAudioBuffer
			{
				AudioBytes = (uint) filledLengthInBytes,
				pAudioData = buffer,
				PlayLength = (
					(uint) (filledLengthInBytes /
					        Format.Channels /
					        (uint) (Format.BitsPerSample / 8))
				)
			};

			Submit(buf);
		}

		if (reachedEnd)
		{
			/* We have reached the end of the data, what do we do? */
			if (Loop)
			{
				AudioData.Seek(0);
			}
		}
	}

	private unsafe void InitializeBuffers()
	{
		BufferSize = AudioData.DecodeBufferSize;

		for (int i = 0; i < BUFFER_COUNT; i += 1)
		{
			if (buffers[i] != IntPtr.Zero)
			{
				NativeMemory.Free((void*) buffers[i]);
			}

			buffers[i] = (IntPtr) NativeMemory.Alloc(BufferSize);
		}
	}

	protected override unsafe void Dispose(bool disposing)
	{
		if (!IsDisposed)
		{
			lock (StateLock)
			{
				Stop();

				for (int i = 0; i < BUFFER_COUNT; i += 1)
				{
					if (buffers[i] != IntPtr.Zero)
					{
						NativeMemory.Free((void*) buffers[i]);
					}
				}
			}
		}
		base.Dispose(disposing);
	}
}