Implement a query filter.

Author: imclint21

src/Initium/Attributes/QueryFilterAttribute.cs

@@ -0,0 +1,51 @@
+using System.Net;
+using System.Reflection;
+using Initium.Exceptions;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.Extensions.Primitives;
+
+namespace Initium.Attributes;
+
+/// <summary>
+/// An attribute to filter query results based on a specified property and enum type.
+/// </summary>
+/// <typeparam name="T">The type of the objects being filtered.</typeparam>
+[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
+public class QueryFilterAttribute<T>(string propertyName, Type propertyType) : Attribute, IActionFilter
+{
+	/// <summary>
+	/// Called before the action method executes. No operation is performed in this implementation.
+	/// </summary>
+	/// <param name="context">The context for the executed action.</param>
+	public void OnActionExecuting(ActionExecutingContext context) { }
+	
+	/// <summary>
+	/// Executes after the action method is invoked. Filters the result based on the specified property and enum value.
+	/// </summary>
+	/// <param name="context">The context for the action filter.</param>
+	public void OnActionExecuted(ActionExecutedContext context)
+	{
+		if (!propertyType.IsEnum)
+			throw new ApiException(HttpStatusCode.BadRequest, $"QueryFilter only accepts enum types for filters. The property '{propertyName}' is not an enum.");
+		
+		if (context.Result is not ObjectResult { Value: IEnumerable<T> enumerable } objectResult) return;
+		
+		var query = context.HttpContext.Request.Query;
+		if (!query.TryGetValue(propertyName, out var parameterValue)) return;
+		
+		if (StringValues.IsNullOrEmpty(parameterValue))
+			throw new ApiException(HttpStatusCode.BadRequest, "FUCK HITLER"); 
+
+		if (!Enum.TryParse(propertyType, parameterValue, ignoreCase: true, out var enumValue))
+			throw new ApiException(HttpStatusCode.BadRequest, $"Invalid query parameter value: `{parameterValue}` for `{propertyName}`. Allowed values are: {string.Join(", ", Enum.GetNames(propertyType))}.");
+
+		objectResult.Value = enumerable.Where(item =>
+		{
+			var property = typeof(T).GetProperty(propertyName, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
+			if (property == null) return false;
+			var value = property.GetValue(item);
+			return value?.Equals(enumValue) == true;
+		});
+	}
+}