From 05ccb4d8f1bbe3fb64e117136b4a89bcfb0b0b33 Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Tue, 27 Oct 2020 19:21:35 +0800
Subject: Split front and back end.

---
 BackEnd/Timeline/Models/Validation/Validator.cs | 127 ++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 BackEnd/Timeline/Models/Validation/Validator.cs

(limited to 'BackEnd/Timeline/Models/Validation/Validator.cs')

diff --git a/BackEnd/Timeline/Models/Validation/Validator.cs b/BackEnd/Timeline/Models/Validation/Validator.cs
new file mode 100644
index 00000000..aef7891c
--- /dev/null
+++ b/BackEnd/Timeline/Models/Validation/Validator.cs
@@ -0,0 +1,127 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using static Timeline.Resources.Models.Validation.Validator;
+
+namespace Timeline.Models.Validation
+{
+    /// <summary>
+    /// A validator to validate value.
+    /// </summary>
+    public interface IValidator
+    {
+        /// <summary>
+        /// Validate given value.
+        /// </summary>
+        /// <param name="value">The value to validate.</param>
+        /// <returns>Validation success or not and message.</returns>
+        (bool, string) Validate(object? value);
+    }
+
+    public static class ValidatorExtensions
+    {
+        public static bool Validate(this IValidator validator, object? value, out string message)
+        {
+            if (validator == null)
+                throw new ArgumentNullException(nameof(validator));
+
+            var (r, m) = validator.Validate(value);
+            message = m;
+            return r;
+        }
+    }
+
+    /// <summary>
+    /// Convenient base class for validator.
+    /// </summary>
+    /// <typeparam name="T">The type of accepted value.</typeparam>
+    /// <remarks>
+    /// Subclass should override <see cref="DoValidate(T)"/> to do the real validation.
+    /// This class will check the nullity and type of value.
+    /// If value is null, it will pass or fail depending on <see cref="PermitNull"/>.
+    /// If value is not null and not of type <typeparamref name="T"/>
+    /// it will fail and not call <see cref="DoValidate(T)"/>.
+    /// 
+    /// <see cref="PermitNull"/> is true by default.
+    /// 
+    /// If you want some other behaviours, write the validator from scratch.
+    /// </remarks>
+    public abstract class Validator<T> : IValidator
+    {
+        protected bool PermitNull { get; set; } = true;
+
+        public (bool, string) Validate(object? value)
+        {
+            if (value == null)
+            {
+                if (PermitNull)
+                    return (true, GetSuccessMessage());
+                else
+                    return (false, ValidatorMessageNull);
+            }
+
+            if (value is T v)
+            {
+                return DoValidate(v);
+            }
+            else
+            {
+                return (false, ValidatorMessageBadType);
+            }
+        }
+
+        protected static string GetSuccessMessage() => ValidatorMessageSuccess;
+
+        protected abstract (bool, string) DoValidate(T value);
+    }
+
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter,
+        AllowMultiple = false)]
+    public class ValidateWithAttribute : ValidationAttribute
+    {
+        private readonly IValidator _validator;
+
+        /// <summary>
+        /// Create with a given validator.
+        /// </summary>
+        /// <param name="validator">The validator used to validate.</param>
+        public ValidateWithAttribute(IValidator validator)
+        {
+            _validator = validator ?? throw new ArgumentNullException(nameof(validator));
+        }
+
+        /// <summary>
+        /// Create the validator with default constructor.
+        /// </summary>
+        /// <param name="validatorType">The type of the validator.</param>
+        public ValidateWithAttribute(Type validatorType)
+        {
+            if (validatorType == null)
+                throw new ArgumentNullException(nameof(validatorType));
+
+            if (!typeof(IValidator).IsAssignableFrom(validatorType))
+                throw new ArgumentException(ValidateWithAttributeExceptionNotValidator, nameof(validatorType));
+
+            try
+            {
+                _validator = (Activator.CreateInstance(validatorType) as IValidator)!;
+            }
+            catch (Exception e)
+            {
+                throw new ArgumentException(ValidateWithAttributeExceptionCreateFail, e);
+            }
+        }
+
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            var (result, message) = _validator.Validate(value);
+            if (result)
+            {
+                return ValidationResult.Success;
+            }
+            else
+            {
+                return new ValidationResult(message);
+            }
+        }
+    }
+}
-- 
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