add: unique characters attribute

familiarly known as UniqueCharsAttr

Models/Validation/UniqueCharsAttr.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using System.Runtime.CompilerServices;
+
+namespace pwt_0x01_ng.Models.Validation
+{
+	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Parameter, AllowMultiple = false)]
+	public class UniqueCharsAttr : ValidationAttribute, IClientModelValidator
+	{
+		public UniqueCharsAttr(){
+		}
+
+		protected override ValidationResult IsValid(object value, ValidationContext validationContext) {
+			if (value is string phrase) {
+				int count = phrase.Distinct().Count();
+				if(count >= config.min_passwd_unique_chars) {
+					return ValidationResult.Success;
+				} else {
+					return new ValidationResult(GetErrorMessage(count, validationContext.MemberName), new List<string> { validationContext.MemberName });
+				}
+			}
+			throw new NotImplementedException($"Attribute {nameof(UniqueCharsAttr)} not implemented for object {value.GetType()}.");
+		}
+
+		protected string GetErrorMessage(int chars, string member_name) => $"not enough unique characters - provided: {chars}, wanted: {config.min_passwd_unique_chars}, problematic field: {member_name}";
+		protected string GetErrorMessage() => $"not enough unique characters. wanted: {config.min_passwd_unique_chars}";
+
+		public void AddValidation(ClientModelValidationContext ctx){
+			MergeAttribute(ctx.Attributes, "data-val", "true");
+			MergeAttribute(ctx.Attributes, "data-val-uniquechars", GetErrorMessage());
+		}
+
+		private bool MergeAttribute(IDictionary<string, string> attributes, string key, string value){
+			if (attributes.ContainsKey(key)){
+				return false;
+			}
+
+			attributes.Add(key, value);
+			return true;
+		}
+	}
+}