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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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