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//
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// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
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//
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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#nullable enable

using System.Collections.Generic;
using System.Linq;

namespace Duplicati.Library.Utility;

/// <summary>
/// Contains extension methods for <see cref="IEnumerable{T}"/>.
/// </summary>
public static class EnumerableExtensions
{
    /// <summary>
    /// Filters a sequence of values to exclude null elements.
    /// </summary>
    /// <param name="source">The sequence to filter.</param>
    /// <returns>A sequence that contains only the non-null elements from the input sequence.</returns>
    public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source)
        => source.Where(x => x != null)
                .Select(x => x!);

    /// <summary>
    /// Filters a sequence of values to exclude null elements.
    /// </summary>
    /// <param name="source">The sequence to filter.</param>
    /// <returns>A sequence that contains only the non-null elements from the input sequence.</returns>
    public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source) where T : struct
        => source.Where(x => x != null)
                .Select(x => x!.Value);

    /// <summary>
    /// Filters a sequence of values to exclude null or whitespace elements.
    /// </summary>
    /// <param name="source">The sequence to filter.</param>
    /// <returns>A sequence that contains only the non-null and non-whitespace elements from the input sequence.</returns>
    public static IEnumerable<string> WhereNotNullOrWhiteSpace(this IEnumerable<string?> source)
        => source.Where(x => !string.IsNullOrWhiteSpace(x))
                .Select(x => x!);
}