DotNetAlpm/Alpm/FileList.cs

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

namespace Foodsoft.Alpm
{
    public struct FileList : IReadOnlyList<File>
    {
        private readonly SafePackageHandle _handle;
        private readonly IntPtr _ptr;

        internal FileList(SafePackageHandle handle, IntPtr ptr)
        {
            _handle = handle;
            _ptr = ptr;
        }

        public File? Contains(string path)
        {
            return _handle.UseHandle(_ptr, ptr =>
            {
                var foundPtr = alpm.alpm_filelist_contains(ptr, path);
                return foundPtr != IntPtr.Zero ? new File(foundPtr) : (File?) null;
            });
        }

        public IEnumerator<File> GetEnumerator()
        {
            var release = false;

            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                _handle.DangerousAddRef(ref release);
                if (!release) throw new ObjectDisposedException(_handle.GetType().FullName);
                var arrayPtr = FileArray(_ptr, out var count);
                for (var i = 0; i < count; ++i) yield return new File(FilePtr(arrayPtr, i));
            }
            finally
            {
                if (release)
                    _handle.DangerousRelease();
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        public int Count => _handle.UseHandle(_ptr, FileCount);

        public File this[int index]
        {
            get
            {
                return _handle.UseHandle(_ptr, ptr =>
                {
                    var arrayPtr = FileArray(ptr, out var count);
                    if (index >= count || index < 0)
                        throw new ArgumentOutOfRangeException(nameof(index), index, $"Exceeds size {count}");
                    return new File(FilePtr(arrayPtr, index));
                });
            }
        }


        [StructLayout(LayoutKind.Sequential)]
        private readonly unsafe struct NativeFileList
        {
            internal readonly UIntPtr count;
            internal readonly File.NativeFile* files;
        }

        private static unsafe IntPtr FilePtr(IntPtr array, int i)
        {
            return (IntPtr) ((File.NativeFile*) array + i);
        }

        private static unsafe IntPtr FileArray(IntPtr ptr, out int count)
        {
            var list = (NativeFileList*) ptr;
            count = (int) list->count;
            return (IntPtr) list->files;
        }

        private static unsafe int FileCount(IntPtr ptr)
        {
            var list = (NativeFileList*) ptr;
            return (int) list->count;
        }
    }
}