namespace IRCTokens;

public static class EnumerableExtensions
{
    public static IEnumerable<byte[]> Split(this byte[] bytes, byte separator)
    {
        if (bytes == null || bytes.Length == 0) return new List<byte[]>();

        var newLineIndices = bytes.Select((b, i) => b == separator ? i : -1).Where(i => i != -1).ToArray();
        var lines          = new byte[newLineIndices.Length + 1][];
        var currentIndex   = 0;
        var arrIndex       = 0;

        for (var i = 0; i < newLineIndices.Length && currentIndex < bytes.Length; ++i)
        {
            var n = new byte[newLineIndices[i] - currentIndex];
            Array.Copy(bytes, currentIndex, n, 0, newLineIndices[i] - currentIndex);
            currentIndex      = newLineIndices[i] + 1;
            lines[arrIndex++] = n;
        }

        // Handle the last string at the end of the array if there is one.
        if (currentIndex < bytes.Length)
            lines[arrIndex] = bytes.Skip(currentIndex).ToArray();
        else if (arrIndex == newLineIndices.Length)
            // We had a separator character at the end of a string.  Rather than just allowing
            // a null character, we'll replace the last element in the array with an empty string.
            lines[arrIndex] = [];

        return lines.ToArray();
    }

    public static byte[] Trim(this IEnumerable<byte> bytes, byte separator)
    {
        if (bytes == null) return [];

        var byteList = new List<byte>(bytes);
        var i        = 0;

        if (!byteList.Any()) return byteList.ToArray();

        while (byteList[i] == separator)
        {
            byteList.RemoveAt(i);
            i++;
        }

        i = byteList.Count - 1;
        while (byteList[i] == separator)
        {
            byteList.RemoveAt(i);
            i--;
        }

        return byteList.ToArray();
    }

#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER))
    /// <summary>
    /// Bypasses a specified number of contiguous elements from the end of the sequence and returns the remaining elements.
    /// </summary>
    /// <typeparam name="TSource">Source sequence element type.</typeparam>
    /// <param name="source">Source sequence.</param>
    /// <param name="count">
    /// The number of elements to skip from the end of the sequence before returning the remaining
    /// elements.
    /// Backported from netcore:
    /// https://github.com/dotnet/reactive/blob/ebab5fc37e8c0888f7b96107852a8794e9af1735/Ix.NET/Source/System.Interactive/System/Linq/Operators/SkipLast.cs
    /// </param>
    /// <returns>Sequence bypassing the specified number of elements counting from the end of the source sequence.</returns>
    public static IEnumerable<TSource> SkipLast<TSource>(this IEnumerable<TSource> source, int count)
    {
        if (source == null)
            throw new ArgumentNullException(nameof(source));
        if (count < 0)
            throw new ArgumentOutOfRangeException(nameof(count));

        return SkipLastCore(source, count);
    }

    private static IEnumerable<TSource> SkipLastCore<TSource>(this IEnumerable<TSource> source, int count)
    {
        var q = new Queue<TSource>();

        foreach (var x in source)
        {
            q.Enqueue(x);

            if (q.Count > count)
            {
                yield return q.Dequeue();
            }
        }
    }
#endif
}