// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
namespace Microsoft.AspNetCore.Components.Forms;
 
/// <summary>
/// Supplies information about an <see cref="InputFile.OnChange"/> event being raised.
/// </summary>
public sealed class InputFileChangeEventArgs : EventArgs
{
    private readonly IReadOnlyList<IBrowserFile> _files;
 
    /// <summary>
    /// Constructs a new <see cref="InputFileChangeEventArgs"/> instance.
    /// </summary>
    /// <param name="files">The list of <see cref="IBrowserFile"/>.</param>
    public InputFileChangeEventArgs(IReadOnlyList<IBrowserFile> files)
    {
        _files = files ?? throw new ArgumentNullException(nameof(files));
    }
 
    /// <summary>
    /// Gets the number of supplied files.
    /// </summary>
    public int FileCount => _files.Count;
 
    /// <summary>
    /// Gets the supplied file. Note that if the input accepts multiple files, then instead of
    /// reading this property, you should call <see cref="GetMultipleFiles(int)"/>.
    /// </summary>
    public IBrowserFile File => _files.Count switch
    {
        0 => throw new InvalidOperationException("No file was supplied."),
        1 => _files[0],
        _ => throw new InvalidOperationException($"More than one file was supplied. Call {nameof(GetMultipleFiles)} to receive multiple files."),
    };
 
    /// <summary>
    /// Gets the file entries list. This method should be used for inputs that accept multiple
    /// files. If the input accepts only a single file, then use the <see cref="File"/> property
    /// instead.
    /// </summary>
    /// <param name="maximumFileCount">The maximum number of files to accept. If the number of files exceeds this value, this method will throw an exception.</param>
    public IReadOnlyList<IBrowserFile> GetMultipleFiles(int maximumFileCount = 10)
    {
        if (_files.Count > maximumFileCount)
        {
            throw new InvalidOperationException($"The maximum number of files accepted is {maximumFileCount}, but {_files.Count} were supplied.");
        }
 
        return _files;
    }
}