// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Options;
 
namespace Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation;
 
internal sealed class RuntimeCompilationFileProvider
{
    private readonly MvcRazorRuntimeCompilationOptions _options;
    private IFileProvider? _compositeFileProvider;
 
    public RuntimeCompilationFileProvider(IOptions<MvcRazorRuntimeCompilationOptions> options)
    {
        ArgumentNullException.ThrowIfNull(options);
 
        _options = options.Value;
    }
 
    public IFileProvider FileProvider
    {
        get
        {
            if (_compositeFileProvider == null)
            {
                _compositeFileProvider = GetCompositeFileProvider(_options);
            }
 
            return _compositeFileProvider;
        }
    }
 
    private static IFileProvider GetCompositeFileProvider(MvcRazorRuntimeCompilationOptions options)
    {
        var fileProviders = options.FileProviders;
        if (fileProviders.Count == 0)
        {
            var message = Resources.FormatFileProvidersAreRequired(
                typeof(MvcRazorRuntimeCompilationOptions).FullName,
                nameof(MvcRazorRuntimeCompilationOptions.FileProviders),
                typeof(IFileProvider).FullName);
            throw new InvalidOperationException(message);
        }
        else if (fileProviders.Count == 1)
        {
            return fileProviders[0];
        }
 
        return new CompositeFileProvider(fileProviders);
    }
}