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

namespace MoonWorks.Audio
{
    /// <summary>
    /// For streaming long playback.
    /// Can be extended to support custom decoders.
    /// </summary>
    public abstract class StreamingSound : SoundInstance
    {
        private readonly List<IntPtr> queuedBuffers = new List<IntPtr>();
        private readonly List<uint> queuedSizes = new List<uint>();
        private const int MINIMUM_BUFFER_CHECK = 3;

        public int PendingBufferCount => queuedBuffers.Count;

        public StreamingSound(
            AudioDevice device,
            ushort channels,
            uint samplesPerSecond,
            bool is3D,
            bool loop
        ) : base(device, channels, samplesPerSecond, is3D, loop) { }

        public override void Play()
        {
            if (State == SoundState.Playing)
            {
                return;
            }

            State = SoundState.Playing;
            Update();
            FAudio.FAudioSourceVoice_Start(Handle, 0, 0);
        }

        public override void Pause()
        {
            if (State == SoundState.Playing)
            {
                FAudio.FAudioSourceVoice_Stop(Handle, 0, 0);
                State = SoundState.Paused;
            }
        }

        public override void Stop(bool immediate = true)
        {
            if (immediate)
            {
                FAudio.FAudioSourceVoice_Stop(Handle, 0, 0);
                FAudio.FAudioSourceVoice_FlushSourceBuffers(Handle);
                ClearBuffers();
            }

            State = SoundState.Stopped;
        }

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

            FAudio.FAudioSourceVoice_GetState(
                Handle,
                out var state,
                FAudio.FAUDIO_VOICE_NOSAMPLESPLAYED
            );

            while (PendingBufferCount > state.BuffersQueued)
                lock (queuedBuffers)
                {
                    Marshal.FreeHGlobal(queuedBuffers[0]);
                    queuedBuffers.RemoveAt(0);
                }

            QueueBuffers();
        }

        protected void QueueBuffers()
        {
            for (
                int i = MINIMUM_BUFFER_CHECK - PendingBufferCount;
                i > 0;
                i -= 1
            )
            {
                AddBuffer();
            }
        }

        protected void ClearBuffers()
        {
            lock (queuedBuffers)
            {
                foreach (IntPtr buf in queuedBuffers)
                {
                    Marshal.FreeHGlobal(buf);
                }
                queuedBuffers.Clear();
                queuedSizes.Clear();
            }
        }

        protected void AddBuffer()
        {
            AddBuffer(
                out var buffer,
                out var bufferOffset,
                out var bufferLength,
                out var reachedEnd
            );

            var lengthInBytes = bufferLength * sizeof(float);

            IntPtr next = Marshal.AllocHGlobal((int) lengthInBytes);
            Marshal.Copy(buffer, (int) bufferOffset, next, (int) bufferLength);

            lock (queuedBuffers)
            {
                queuedBuffers.Add(next);
                if (State != SoundState.Stopped)
                {
                    FAudio.FAudioBuffer buf = new FAudio.FAudioBuffer
                    {
                        AudioBytes = lengthInBytes,
                        pAudioData = next,
                        PlayLength = (
                            lengthInBytes /
                            Format.nChannels /
                            (uint)(Format.wBitsPerSample / 8)
                        )
                    };

                    FAudio.FAudioSourceVoice_SubmitSourceBuffer(
                        Handle,
                        ref buf,
                        IntPtr.Zero
                    );
                }
                else
                {
                    queuedSizes.Add(lengthInBytes);
                }
            }

            /* We have reached the end of the file, what do we do? */
            if (reachedEnd)
            {
                if (Loop)
                {
                    SeekStart();
                }
                else
                {
                    Stop(false);
                }
            }
        }

        protected abstract void AddBuffer(
            out float[] buffer,
            out uint bufferOffset, /* in floats */
            out uint bufferLength, /* in floats */
            out bool reachedEnd
        );

        protected abstract void SeekStart();

        protected override void Destroy()
        {
            Stop(true);
        }
    }
}