using System;
using System.Linq.Expressions;

namespace Microsoft.AspNetCore.Mvc.ModelBinding
{
	/// <summary>
	/// Provides extension methods for the ASP.NET Core application.
	/// </summary>
	public static class ModelStateDictionaryExtensions
	{
		/// <summary>
		/// Adds the specified <paramref name="errorMessage"/> to the <see cref="ModelStateEntry.Errors"/>
		/// instance that is associated with the key specified as a <see cref="MemberExpression"/>.
		/// </summary>
		/// <typeparam name="TModel">The type of the model.</typeparam>
		/// <typeparam name="TProperty">The type of the property.</typeparam>
		/// <param name="modelState">The <see cref="ModelStateDictionary"/> instance.</param>
		/// <param name="model">The model. Only used to infer the model type.</param>
		/// <param name="keyExpression">The <see cref="MemberExpression"/> that specifies the property.</param>
		/// <param name="errorMessage">The error message to add.</param>
		/// <exception cref="InvalidOperationException">No member expression provided.</exception>
		public static void AddModelError<TModel, TProperty>(this ModelStateDictionary modelState, TModel model, Expression<Func<TModel, TProperty>> keyExpression, string errorMessage)
		{
			if (modelState is null)
				throw new ArgumentNullException(nameof(modelState));

			string key = "";
			var expr = keyExpression.Body as MemberExpression;
			while (expr != null)
			{
				key = expr.Member.Name + (key != "" ? "." + key : "");
				expr = expr.Expression as MemberExpression;
			}
			if (key == "")
				throw new InvalidOperationException("No member expression provided.");

			modelState.AddModelError(key, errorMessage);
		}
	}
}