using System;
using System.Runtime.InteropServices;

namespace Susurrus.XAudio2
{
    /// <summary>
    /// A voice the engine made, which stays valid until it is destroyed.
    /// </summary>
    public abstract class XAudio2Voice
    {
        [UnmanagedFunctionPointer(CallingConvention.StdCall)]
        private delegate void DestroyCall(IntPtr self);

        private readonly DestroyCall destroy;
        private IntPtr handle;

        /// <summary>
        /// Gets the native object's address, which is zero once the voice is destroyed.
        /// </summary>
        protected IntPtr Handle => handle;

        public bool IsDestroyed => handle == IntPtr.Zero;

        protected XAudio2Voice(IntPtr handle)
        {
            this.destroy = Vtable.Bind<DestroyCall>(handle, VoiceSlots.DestroyVoice);
            this.handle = handle;
        }

        /// <summary>
        /// Throws if the voice has been destroyed, since its native object is then gone.
        /// </summary>
        protected void ThrowIfDestroyed()
        {
            if (handle == IntPtr.Zero)
            {
                throw new ObjectDisposedException(GetType().Name, "This voice has been destroyed.");
            }
        }

        /// <summary>
        /// Frees the native voice.  Does nothing if it is already destroyed.
        /// </summary>
        public void Destroy()
        {
            if (handle == IntPtr.Zero)
            {
                return;
            }

            IntPtr native = handle;
            handle = IntPtr.Zero;
            destroy(native);
        }
    }
}