DotNetAlpm/Alpm/EnumerableWrapper`3.cs

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

namespace Foodsoft.Alpm
{
    internal static class EnumerableWrapper<TElement>
    {
        internal static EnumerableWrapper<TElement, TImpl> Create<TImpl>(TImpl impl)
            where TImpl : struct, ICollectionImpl<TElement>
        {
            return new EnumerableWrapper<TElement, TImpl>(impl);
        }
    }

    internal struct EnumerableWrapper<TElement, TImpl> : ICollection<TElement> where TImpl : struct,
        ICollectionImpl<TElement>
    {
        private TImpl _impl;

        public static EnumerableWrapper<TElement, TImpl> Create(TImpl impl)
        {
            return new EnumerableWrapper<TElement, 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();

        public int Count
        {
            get
            {
                var impl = _impl;
                return impl.Handle.UseHandle((_) => (int) alpm.alpm_list_count(impl.GetItems()));
            }
        }

        public bool Contains(TElement item)
        {
            var impl = _impl;
            switch (item)
            {
                case string s:
                    return impl.Handle.UseHandle((_) => alpm.alpm_list_find_str(impl.GetItems(), s) != (IntPtr.Zero));
                default:
                    var comparer = EqualityComparer<TElement>.Default;
                    return _impl.Handle.UseHandle((_) =>
                    {
                        for (var list = impl.GetItems(); list != IntPtr.Zero; list = Wrapper.ListNext(list))
                        {
                            if (comparer.Equals(item, impl.PtrToItem(Wrapper.ListData(list))))
                                return true;
                        }

                        return false;
                    });
            }
        }

        public void CopyTo(TElement[] array, int arrayIndex)
        {
            var impl = _impl;
            impl.Handle.UseHandle((_) =>
            {
                for (var list = impl.GetItems(); list != IntPtr.Zero; list = Wrapper.ListNext(list))
                {
                    array[arrayIndex++] = impl.PtrToItem(Wrapper.ListData(list));
                }

                return arrayIndex;
            });
        }

        public void Add(TElement item)
        {
            throw new NotSupportedException();
        }

        public void Clear()
        {
            throw new NotSupportedException();
        }

        public bool Remove(TElement item)
        {
            throw new NotSupportedException();
        }

        public bool IsReadOnly => true;
    }
}