src/marlin.web/TagHelpers/ActiveLinkTagHelper.cs


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namespace marlin.web.TagHelpers;

using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;

[HtmlTargetElement("a", Attributes = "active-when")]
public class ActiveLinkTagHelper : TagHelper
{
    [HtmlAttributeName("asp-controller")]
    public string Controller { get; set; }

    [HtmlAttributeName("asp-action")]
    public string Action { get; set; }
    
    [HtmlAttributeName("active-when")]
    public ActiveLinkWhen ActiveWhen { get; set; }

    [ViewContext]
    [HtmlAttributeNotBound]
    public ViewContext ViewContext { get; set; }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        var currentController = ViewContext.RouteData.Values["controller"]?.ToString();
        var currentAction = ViewContext.RouteData.Values["action"]?.ToString();

        if (!string.Equals(currentController, Controller, StringComparison.OrdinalIgnoreCase))
            return;

        if (!string.Equals(currentAction, Action, StringComparison.OrdinalIgnoreCase)
            && this.ActiveWhen == ActiveLinkWhen.ControllerAndAction)
            return;

        var existingClasses = output.Attributes["class"]?.Value?.ToString() ?? "";
        output.Attributes.SetAttribute("class", $"{existingClasses} active".Trim());
    }
}

public enum ActiveLinkWhen
{
    Controller,
    ControllerAndAction
}