using System;

namespace Susurrus.XAudio2
{
    /// <summary>
    /// Source voices that share one format, handed out and taken back.
    /// </summary>
    public class SourceVoicePool
    {
        private readonly SourceVoice[] all;
        private readonly SourceVoice[] idle;
        private int idleCount;

        public int ChannelCount { get; }

        public SampleFormat Format { get; }

        /// <summary>
        /// Gets how many voices the pool holds, in use or not.
        /// </summary>
        public int Capacity => all.Length;

        public SourceVoicePool(int channelCount, SampleFormat format, SourceVoice[] voices)
        {
            if (voices == null)
            {
                throw new ArgumentNullException(nameof(voices));
            }

            ChannelCount = channelCount;
            Format = format;
            all = (SourceVoice[])voices.Clone();
            idle = (SourceVoice[])voices.Clone();
            idleCount = idle.Length;
        }

        /// <summary>
        /// Takes an idle voice out of the pool.  Returns null when every voice is in use.
        /// </summary>
        public SourceVoice Take()
        {
            if (idleCount == 0)
            {
                return null;
            }

            return idle[--idleCount];
        }

        /// <summary>
        /// Puts a voice taken from this pool back.  Returning one that isn't in use, or that came from elsewhere,
        /// throws.
        /// </summary>
        public void Return(SourceVoice voice)
        {
            bool isOurs = Array.IndexOf(all, voice) >= 0;
            bool isIdle = Array.IndexOf(idle, voice, 0, idleCount) >= 0;

            if (!isOurs || isIdle)
            {
                throw new ArgumentException("That voice isn't one this pool has handed out.", nameof(voice));
            }

            idle[idleCount++] = voice;
        }

        /// <summary>
        /// Destroys every voice, including those in use.
        /// </summary>
        public void Destroy()
        {
            for (int i = 0; i < all.Length; ++i)
            {
                all[i].Destroy();
            }

            idleCount = 0;
        }
    }
}