BrowserFileExtensions.cs

// 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>
/// Contains helper methods for <see cref="IBrowserFile"/>.
/// </summary>
public static class BrowserFileExtensions
{
    /// <summary>
    /// Attempts to convert the current image file to a new one of the specified file type and maximum file dimensions.
    /// <para>
    /// Caution: there is no guarantee that the file will be converted, or will even be a valid image file at all, either
    /// before or after conversion. The conversion is requested within the browser before it is transferred to .NET
    /// code, so the resulting data should be treated as untrusted.
    /// </para>
    /// </summary>
    /// <remarks>
    /// The image will be scaled to fit the specified dimensions while preserving the original aspect ratio.
    /// </remarks>
    /// <param name="browserFile">The <see cref="IBrowserFile"/> to convert to a new image file.</param>
    /// <param name="format">The new image format.</param>
    /// <param name="maxWidth">The maximum image width.</param>
    /// <param name="maxHeight">The maximum image height</param>
    /// <returns>A <see cref="ValueTask"/> representing the completion of the operation.</returns>
    public static ValueTask<IBrowserFile> RequestImageFileAsync(this IBrowserFile browserFile, string format, int maxWidth, int maxHeight)
    {
        if (browserFile is BrowserFile browserFileInternal)
        {
            return browserFileInternal.Owner.ConvertToImageFileAsync(browserFileInternal, format, maxWidth, maxHeight);
        }

        throw new InvalidOperationException($"Cannot perform this operation on custom {typeof(IBrowserFile)} implementations.");
    }
}