free-code-dotnet/tests/FreeCode.Tests.Unit/Models/OperationResultAndTokenUsageTests.cs

using Xunit;
using FluentAssertions;
using NSubstitute;
using System.Collections.Generic;
using FreeCode.Core.Models;

namespace FreeCode.Tests.Unit.Models;

public sealed class OperationResultAndTokenUsageTests
{
    [Fact]
    public void PermissionResult_Allowed_ReturnsAllowedWithNullReason()
    {
        var result = PermissionResult.Allowed();

        result.IsAllowed.Should().BeTrue();
        result.Reason.Should().BeNull();
    }

    [Fact]
    public void PermissionResult_Denied_ReturnsDeniedWithReason()
    {
        var result = PermissionResult.Denied("not allowed");

        result.IsAllowed.Should().BeFalse();
        result.Reason.Should().Be("not allowed");
    }

    [Fact]
    public void PermissionResult_Constructor_CanCreateAllowedWithReason()
    {
        var result = new PermissionResult(true, "manual");

        result.IsAllowed.Should().BeTrue();
        result.Reason.Should().Be("manual");
    }

    [Fact]
    public void PermissionResult_UsesValueEquality()
    {
        var left = PermissionResult.Denied("reason");
        var right = PermissionResult.Denied("reason");

        left.Should().Be(right);
    }

    [Fact]
    public void ValidationResult_Success_ReturnsValidWithoutErrors()
    {
        var result = ValidationResult.Success();

        result.IsValid.Should().BeTrue();
        result.Errors.Should().BeEmpty();
    }

    [Fact]
    public void ValidationResult_Failure_ReturnsInvalidWithSingleError()
    {
        var result = ValidationResult.Failure(["missing field"]);

        result.IsValid.Should().BeFalse();
        result.Errors.Should().ContainSingle().Which.Should().Be("missing field");
    }

    [Fact]
    public void ValidationResult_Failure_PreservesErrorOrder()
    {
        var result = ValidationResult.Failure(["first", "second", "third"]);

        result.Errors.Should().ContainInOrder("first", "second", "third");
    }

    [Fact]
    public void ValidationResult_Failure_AllowsEmptyEnumerable()
    {
        var result = ValidationResult.Failure([]);

        result.IsValid.Should().BeFalse();
        result.Errors.Should().BeEmpty();
    }

    [Fact]
    public void ValidationResult_Success_UsesValueEquality()
    {
        var left = ValidationResult.Success();
        var right = ValidationResult.Success();

        left.Should().Be(right);
    }

    [Fact]
    public void ValidationResult_Failure_CopiesInputSequence()
    {
        var errors = new List<string> { "first" };

        var result = ValidationResult.Failure(errors);
        errors.Add("second");

        result.Errors.Should().ContainSingle().Which.Should().Be("first");
    }

    [Fact]
    public void TokenUsage_HoldsAllCounts()
    {
        var usage = new TokenUsage(10, 20, 30, 40);

        usage.InputTokens.Should().Be(10);
        usage.OutputTokens.Should().Be(20);
        usage.CacheCreationTokens.Should().Be(30);
        usage.CacheReadTokens.Should().Be(40);
    }

    [Fact]
    public void TokenUsage_UsesValueEquality()
    {
        var left = new TokenUsage(1, 2, 3, 4);
        var right = new TokenUsage(1, 2, 3, 4);

        left.Should().Be(right);
    }

    [Fact]
    public void TokenUsage_DeconstructsIntoOriginalValues()
    {
        var usage = new TokenUsage(1, 2, 3, 4);

        var (input, output, cacheCreation, cacheRead) = usage;

        input.Should().Be(1);
        output.Should().Be(2);
        cacheCreation.Should().Be(3);
        cacheRead.Should().Be(4);
    }

    [Fact]
    public void TokenUsage_AllowsZeroCounts()
    {
        var usage = new TokenUsage(0, 0, 0, 0);

        usage.Should().Be(new TokenUsage(0, 0, 0, 0));
    }

    [Fact]
    public void TokenUsage_PassivelyStoresNegativeCounts()
    {
        var usage = new TokenUsage(-1, -2, -3, -4);

        usage.InputTokens.Should().Be(-1);
        usage.OutputTokens.Should().Be(-2);
        usage.CacheCreationTokens.Should().Be(-3);
        usage.CacheReadTokens.Should().Be(-4);
    }

    [Fact]
    public void TokenUsage_CanBeSummedByConsumerCode()
    {
        var usage = new TokenUsage(10, 20, 30, 40);

        var total = usage.InputTokens + usage.OutputTokens + usage.CacheCreationTokens + usage.CacheReadTokens;

        total.Should().Be(100);
    }

    [Fact]
    public void TokenUsage_CanBeStoredInsideASubstituteConsumer()
    {
        var usage = new TokenUsage(2, 4, 6, 8);
        var holder = new TokenUsageHolder(usage);

        holder.Usage.Should().Be(usage);
    }

    private sealed class TokenUsageHolder(TokenUsage usage) : ITokenUsageHolder
    {
        public TokenUsage Usage { get; } = usage;
    }

    public interface ITokenUsageHolder
    {
        TokenUsage Usage { get; }
    }
}