// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

#nullable disable

using System.Threading.Tasks;

namespace Microsoft.AspNetCore.Razor.TagHelpers;

/// <summary>
/// Contract used to modify an HTML element.
/// </summary>
public interface ITagHelperComponent
{
    /// <summary>
    /// When a set of <see cref="ITagHelperComponent"/>s are executed, their <see cref="Init(TagHelperContext)"/>'s
    /// are first invoked in the specified <see cref="Order"/>; then their
    /// <see cref="ProcessAsync(TagHelperContext, TagHelperOutput)"/>'s are invoked in the specified
    /// <see cref="Order"/>. Lower values are executed first.
    /// </summary>
    int Order { get; }

    /// <summary>
    /// Initializes the <see cref="ITagHelperComponent"/> with the given <paramref name="context"/>. Additions to
    /// <see cref="TagHelperContext.Items"/> should be done within this method to ensure they're added prior to
    /// executing the children.
    /// </summary>
    /// <param name="context">Contains information associated with the current HTML tag.</param>
    /// <remarks>When more than one <see cref="ITagHelperComponent"/> runs on the same element,
    /// <see cref="M:TagHelperOutput.GetChildContentAsync"/> may be invoked prior to <see cref="ProcessAsync"/>.
    /// </remarks>
    void Init(TagHelperContext context);

    /// <summary>
    /// Asynchronously executes the <see cref="ITagHelperComponent"/> with the given <paramref name="context"/> and
    /// <paramref name="output"/>.
    /// </summary>
    /// <param name="context">Contains information associated with the current HTML tag.</param>
    /// <param name="output">A stateful HTML element used to generate an HTML tag.</param>
    /// <returns>A <see cref="Task"/> that on completion updates the <paramref name="output"/>.</returns>
    Task ProcessAsync(TagHelperContext context, TagHelperOutput output);
}
