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

namespace Foodsoft.Alpm
{
    internal struct EnumerableWrapper<TImpl, TElement, THandle> : IEnumerable<TElement> where TImpl : struct,
        IItemsReader<TElement, THandle>
        where THandle : SafeHandle
    {
        private TImpl _impl;

        public EnumerableWrapper(TImpl impl)
        {
            _impl = impl;
        }

        public IEnumerator<TElement> GetEnumerator()
        {
            var handle = _impl.Handle;
            var release = false;

            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                handle.DangerousAddRef(ref release);
                if (!release) throw new ObjectDisposedException(_impl.GetType().FullName);
                for (var list = _impl.GetItems(); list != IntPtr.Zero; list = Wrapper.ListNext(list))
                {
                    yield return _impl.PtrToItem(Wrapper.ListData(list));
                }
            }
            finally
            {
                if (release)
                    handle.DangerousRelease();
            }
        }

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }
}