From ec74a3c491d361bbaf9354b7f17be750b7b8823c Mon Sep 17 00:00:00 2001
From: 杨宇千 <crupest@outlook.com>
Date: Sat, 17 Aug 2019 19:25:08 +0800
Subject: Add validation.

---
 Timeline/Models/Validation/Validator.cs | 107 ++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 Timeline/Models/Validation/Validator.cs

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

diff --git a/Timeline/Models/Validation/Validator.cs b/Timeline/Models/Validation/Validator.cs
new file mode 100644
index 00000000..a1acbed9
--- /dev/null
+++ b/Timeline/Models/Validation/Validator.cs
@@ -0,0 +1,107 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace Timeline.Models.Validation
+{
+    /// <summary>
+    /// A validator to validate value.
+    /// See <see cref="Validate(object, out string)"/>.
+    /// </summary>
+    public interface IValidator
+    {
+        /// <summary>
+        /// Validate given value.
+        /// </summary>
+        /// <param name="value">The value to validate.</param>
+        /// <param name="message">The validation message.</param>
+        /// <returns>True if validation passed. Otherwise false.</returns>
+        bool Validate(object value, out string message);
+    }
+
+    public static class ValidationConstants
+    {
+        public const string SuccessMessage = "Validation succeeded.";
+    }
+
+    /// <summary>
+    /// Convenient base class for validator.
+    /// </summary>
+    /// <typeparam name="T">The type of accepted value.</typeparam>
+    /// <remarks>
+    /// Subclass should override <see cref="DoValidate(T, out string)"/> to do the real validation.
+    /// This class will check the nullity and type of value. If value is null or not of type <typeparamref name="T"/>
+    /// it will return false and not call <see cref="DoValidate(T, out string)"/>.
+    /// 
+    /// If you want some other behaviours, write the validator from scratch.
+    /// </remarks>
+    public abstract class Validator<T> : IValidator
+    {
+        public bool Validate(object value, out string message)
+        {
+            if (value == null)
+            {
+                message = "Value is null.";
+                return false;
+            }
+
+            if (value is T v)
+            {
+
+                return DoValidate(v, out message);
+            }
+            else
+            {
+                message = $"Value is not of type {typeof(T).Name}";
+                return false;
+            }
+        }
+
+        protected abstract bool DoValidate(T value, out string message);
+    }
+
+    [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("Given type is not assignable to IValidator.", nameof(validatorType));
+
+            try
+            {
+                _validator = Activator.CreateInstance(validatorType) as IValidator;
+            }
+            catch (Exception e)
+            {
+                throw new ArgumentException("Failed to create a validator instance from default constructor. See inner exception.", e);
+            }
+        }
+
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            if (_validator.Validate(value, out var message))
+                return ValidationResult.Success;
+            else
+                return new ValidationResult(string.Format("Field {0} is bad. {1}", validationContext.DisplayName, message));
+        }
+    }
+}
-- 
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