recyclarr/src/Recyclarr.Common/Extensions/CollectionExtensions.cs

using System.Collections;

namespace Recyclarr.Common.Extensions;

public static class CollectionExtensions
{
    // From: https://stackoverflow.com/a/34362585/157971
    public static IReadOnlyCollection<T> AsReadOnly<T>(this ICollection<T> source)
    {
        if (source is null)
        {
            throw new ArgumentNullException(nameof(source));
        }

        return source as IReadOnlyCollection<T> ?? new ReadOnlyCollectionAdapter<T>(source);
    }

    // From: https://stackoverflow.com/a/34362585/157971
    private sealed class ReadOnlyCollectionAdapter<T> : IReadOnlyCollection<T>
    {
        private readonly ICollection<T> _source;

        public ReadOnlyCollectionAdapter(ICollection<T> source)
        {
            _source = source;
        }

        public int Count => _source.Count;

        public IEnumerator<T> GetEnumerator()
        {
            return _source.GetEnumerator();
        }

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

    public static void AddRange<T>(this ICollection<T> destination, IEnumerable<T> source)
    {
        foreach (var item in source)
        {
            destination.Add(item);
        }
    }

    public static IEnumerable<T> NotNull<T>(this IEnumerable<T?> source)
        where T : class
    {
        return source.Where(x => x is not null).Select(x => x!);
    }

    public static IEnumerable<T> NotNull<T>(this IEnumerable<T?> source)
        where T : struct
    {
        return source.Where(x => x is not null).Select(x => x!.Value);
    }

    public static bool IsEmpty<T>(this ICollection<T>? collection)
    {
        return collection is null or {Count: 0};
    }

    public static bool IsEmpty<T>(this IReadOnlyCollection<T>? collection)
    {
        return collection is null or {Count: 0};
    }

    public static bool IsNotEmpty<T>(this ICollection<T>? collection)
    {
        return collection is {Count: > 0};
    }

    public static IList<T>? ToListOrNull<T>(this IEnumerable<T> source)
    {
        var list = source.ToList();
        return list.Any() ? list : null;
    }
}