using System;

namespace MoonWorks.Audio
{
	public abstract class StreamingVoice : SourceVoice
	{
		private const int BUFFER_COUNT = 3;
		private readonly IntPtr[] buffers;
		private int nextBufferIndex = 0;
		private uint BufferSize;

		public bool Loop { get; set; }

		public StreamingVoice(AudioDevice device, Format format, uint bufferSize) : base(device, format)
		{
			BufferSize = bufferSize;
		}

		internal unsafe void Update()
		{
			lock (StateLock)
			{
				if (!IsDisposed)
				{
					if (State != SoundState.Playing)
					{
						return;
					}

					QueueBuffers();
				}
			}
		}

		protected void QueueBuffers()
		{
			var buffersQueued = BuffersQueued;
			for (int i = 0; i < BUFFER_COUNT - buffersQueued; i += 1)
			{
				AddBuffer();
			}
		}

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

			FillBuffer(
				(void*) buffer,
				(int) BufferSize,
				out int filledLengthInBytes,
				out bool reachedEnd
			);

			if (filledLengthInBytes > 0)
			{
				var 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)
				{
					SeekStart();
					AddBuffer();
				}
			}
		}

		protected unsafe abstract void FillBuffer(
			void* buffer,
			int bufferLengthInBytes, /* in bytes */
			out int filledLengthInBytes, /* in bytes */
			out bool reachedEnd
		);

		protected abstract void SeekStart();
	}
}