duplicati/Duplicati/Library/SourceProvider/Builtin/Combiner.cs

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using System.Runtime.CompilerServices;
using Duplicati.Library.Interface;

namespace Duplicati.Library.SourceProvider;

/// <summary>
/// Helper class that wraps multiple source providers into a single source provider
/// </summary>
public class Combiner(IEnumerable<ISourceProvider> providers) : ISourceProvider
{
    /// <inheritdoc/>
    public string MountedPath => string.Empty;

    /// <summary>
    /// The providers to combine
    /// </summary>
    private readonly List<ISourceProvider> providers = providers.SelectMany(x => x is Combiner c ? c.providers.AsEnumerable() : [x]).ToList();

    /// <inheritdoc/>
    public Task Initialize(CancellationToken cancellationToken)
        => Task.WhenAll(providers.Select(x => x.Initialize(cancellationToken)));

    /// <inheritdoc />
    public async IAsyncEnumerable<ISourceProviderEntry> Enumerate([EnumeratorCancellation] CancellationToken cancellationToken)
    {
        foreach (var provider in providers)
        {
            await foreach (var entry in provider.Enumerate(cancellationToken).ConfigureAwait(false))
                yield return entry;
        }
    }

    /// <summary>
    /// Provides access to the combined providers
    /// </summary>
    public IEnumerable<ISourceProvider> Providers => providers;

    /// <summary>
    /// Gets a filesystem entry for a given path
    /// </summary>
    /// <param name="path">The path to get</param>
    /// <param name="isFolder">True if the path is a folder</param>
    /// <param name="cancellationToken">The cancellation token</param>
    /// <returns>The filesystem entry</returns>
    public async Task<ISourceProviderEntry?> GetEntry(string path, bool isFolder, CancellationToken cancellationToken)
    {
        foreach (var provider in providers)
            if (!string.IsNullOrWhiteSpace(MountedPath) && provider.MountedPath.StartsWith(path))
            {
                var subpath = provider.MountedPath.Substring(path.Length);
                return await provider.GetEntry(subpath, isFolder, cancellationToken).ConfigureAwait(false);
            }

        foreach (var provider in providers.Where(x => string.IsNullOrWhiteSpace(x.MountedPath)))
        {
            var res = await provider.GetEntry(path, isFolder, cancellationToken).ConfigureAwait(false);
            if (res != null)
                return res;
        }

        return null;
    }

    /// <summary>
    /// Creates a combined source provider from a list of providers
    /// </summary>
    /// <param name="providers">The providers to combine</param>
    /// <returns>The combined provider</returns>
    public static ISourceProvider Combine(IEnumerable<ISourceProvider> providers)
    {
        var providerTotal = providers.SelectMany(x => x is Combiner c ? c.providers.AsEnumerable() : [x]).ToList();
        return providerTotal.Count == 1 ? providerTotal[0] : new Combiner(providers);
    }

    /// <inheritdoc/>
    public void Dispose()
    {
        foreach (var provider in providers)
            provider.Dispose();
    }
}