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using System;
using System.ComponentModel.DataAnnotations;
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 is null)
{
if (PermitNull)
return (true, GetSuccessMessage());
else
return (false, Resource.CantBeNull);
}
if (value is T v)
{
return DoValidate(v);
}
else
{
return (false, string.Format(Resource.NotOfType, typeof(T).Name));
}
}
protected static string GetSuccessMessage() => Resource.ValidationPassed;
protected abstract (bool, string) DoValidate(T value);
}
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter,
AllowMultiple = false)]
public class ValidateWithAttribute : ValidationAttribute
{
protected 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(Resource.ValidateWithAttributeExceptionNotValidator, nameof(validatorType));
try
{
_validator = (Activator.CreateInstance(validatorType) as IValidator)!;
}
catch (Exception e)
{
throw new ArgumentException(Resource.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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