ValidationExample.cs

using Trellis.Primitives;

namespace Example;

using System.Collections.Immutable;
using Trellis;
using static EnsureExtensions;
using static Trellis.ValidationError;

public class ValidationExample
{
    [Fact]
    public void Validation_successful_Test()
    {
        var createdAt = DateTime.UtcNow;
        var updatedAt = createdAt;

        var actual = EmailAddress.TryCreate("xavier@somewhere.com")
            .Combine(FirstName.TryCreate("Xavier"))
            .Combine(LastName.TryCreate("John"))
            .Combine(Ensure(createdAt <= updatedAt, Error.Validation("updateAt cannot be less than createdAt")))
            .Bind((email, firstName, lastName) => Result.Success(string.Join(" ", firstName, lastName, email)));

        actual.Value.Should().Be("Xavier John xavier@somewhere.com");
    }

    [Fact]
    public void Validation_failed_Test()
    {
        // Arrange
        ImmutableArray<FieldError> expected = [
            new("lastName", ["Last Name cannot be empty."]),
            new("email", ["Email address is not valid."]),
            new("updatedAt", ["updateAt cannot be less than createdAt"]),
        ];

        var createdAt = DateTime.UtcNow;
        var updatedAt = createdAt.AddMinutes(-10);

        //Act
        var actual = FirstName.TryCreate("Xavier")
            .Combine(LastName.TryCreate(string.Empty))
            .Combine(EmailAddress.TryCreate("xavier @ somewhereelse.com"))
            .Combine(Ensure(createdAt <= updatedAt, Error.Validation("updateAt cannot be less than createdAt", nameof(updatedAt))))
            .Bind((firstName, lastName, email) =>
            {
                true.Should().BeFalse("this code should not get executed");
                return Result.Success(string.Join(" ", firstName, lastName, email));
            });
        // Assert
        actual.IsFailure.Should().BeTrue();
        var validationErrors = (ValidationError)actual.Error;
        validationErrors.FieldErrors.Should().HaveCount(3);
        validationErrors.FieldErrors.Should().BeEquivalentTo(expected);
    }

    [Fact]
    public void Convert_optional_primitive_type_to_valid_objects()
    {
        string? firstName = null; // Optional so null is allowed.
        string email = "xavier@somewhere.com";
        string? lastName = "John";

        var actual = EmailAddress.TryCreate(email)
            .Combine(Maybe.Optional(firstName, s => FirstName.TryCreate(s)))
            .Combine(Maybe.Optional(lastName, s => LastName.TryCreate(s)))
            .Bind(Add);

        actual.Value.Should().Be("xavier@somewhere.com  John");

        static Result<string> Add(EmailAddress emailAddress, Maybe<FirstName> firstname, Maybe<LastName> lastname)
            => emailAddress + " " + firstname + " " + lastname;
    }

    [Fact]
    public void Cannot_convert_optional_invalid_primitive_type_to_valid_objects()
    {
        string? firstName = string.Empty; // Optional but empty string is not a valid first name.
        string email = "xavier@somewhere.com";
        string? lastName = "John";

        var actual = EmailAddress.TryCreate(email)
            .Combine(Maybe.Optional(firstName, s => FirstName.TryCreate(s)))
            .Combine(Maybe.Optional(lastName, s => LastName.TryCreate(s)))
            .Bind(Add);

        actual.IsFailure.Should().BeTrue();
        actual.Error.Should().BeOfType<ValidationError>();
        var validationError = (ValidationError)actual.Error;
        validationError.FieldErrors[0].Details[0].Should().Be("First Name cannot be empty.");

        static Result<string> Add(EmailAddress emailAddress, Maybe<FirstName> firstname, Maybe<LastName> lastname)
            => emailAddress + " " + firstname + " " + lastname;
    }
}