oecs-sharp/Game.TicTacToe.Tests/SnapshotTests.cs

using FluentAssertions;
using Game.TicTacToe;
using OECS;
using R3;
using Xunit;
using Xunit.Abstractions;

namespace Game.TicTacToe.Tests;

/// <summary>
/// Baseline snapshot and log tests for TicTacToe.
/// Captures the world state as text and R3 change logs so they can be
/// reviewed manually and compared across changes.
/// </summary>
public class SnapshotTests
{
    private readonly ITestOutputHelper _output;

    public SnapshotTests(ITestOutputHelper output)
    {
        _output = output;
    }

    [Fact]
    public void Snapshot_InitialBoard()
    {
        var world = new World();
        for (int r = 0; r < 3; r++)
            for (int c = 0; c < 3; c++)
                world.AddComponent(world.CreateEntity(), new Cell { Row = r, Col = c });

        world.SetSingleton(new GameState
        {
            CurrentPlayer = Player.X,
            Status = GameStatus.Playing,
            MoveCount = 0
        });

        var snapshot = SnapshotWorld(world);
        _output.WriteLine(snapshot);

        // Verify baseline properties.
        snapshot.Should().Contain("GameState: X's turn, 0 moves");
        snapshot.Should().Contain("Cells: 9 total, 0 marked");
    }

    [Fact]
    public void Snapshot_AfterThreeMoves()
    {
        var (world, group) = SetupGame();

        // X: (0,0), O: (1,1), X: (2,2)
        PlayMoves(world, group, (0, 0), (1, 1), (2, 2));

        var snapshot = SnapshotWorld(world);
        _output.WriteLine(snapshot);

        snapshot.Should().Contain("GameState: O's turn, 3 moves");
        snapshot.Should().Contain("Cells: 9 total, 3 marked");
        snapshot.Should().Contain("(0,0): X");
        snapshot.Should().Contain("(1,1): O");
        snapshot.Should().Contain("(2,2): X");
    }

    [Fact]
    public void Snapshot_XWins()
    {
        var (world, group) = SetupGame();

        // X: (0,0), O: (1,0), X: (0,1), O: (1,1), X: (0,2) → X wins row 0
        PlayMoves(world, group, (0, 0), (1, 0), (0, 1), (1, 1), (0, 2));

        var snapshot = SnapshotWorld(world);
        _output.WriteLine(snapshot);

        snapshot.Should().Contain("GameState: XWon");
        snapshot.Should().Contain("Cells: 9 total, 5 marked");
    }

    [Fact]
    public void Snapshot_Draw()
    {
        var (world, group) = SetupGame();

        PlayMoves(world, group,
            (0, 0), (0, 1), (0, 2),
            (1, 1), (1, 0), (1, 2),
            (2, 1), (2, 0), (2, 2));

        var snapshot = SnapshotWorld(world);
        _output.WriteLine(snapshot);

        snapshot.Should().Contain("GameState: Draw");
        snapshot.Should().Contain("Cells: 9 total, 9 marked");
    }

    [Fact]
    public void Log_ReactivityDuringGame()
    {
        var (world, group) = SetupGame();
        var log = new List<string>();

        // Subscribe to all entity-level changes.
        world.ObserveEntityChanges().Subscribe(change =>
        {
            log.Add($"[entity] {change}");
        });

        // Subscribe to component-specific changes.
        world.ObserveComponentChanges<Mark>().Subscribe(change =>
        {
            log.Add($"[mark] {change}");
        });

        world.ObserveComponentChanges<GameState>().Subscribe(change =>
        {
            log.Add($"[gamestate] {change}");
        });

        // Play a full game: X wins on row 0.
        PlayMoves(world, group, (0, 0), (1, 0), (0, 1), (1, 1), (0, 2));

        var logText = string.Join("\n", log);
        _output.WriteLine(logText);

        // Verify key events appear in the log.
        log.Should().Contain(l => l.Contains("ComponentAdded") && l.Contains("Mark"));
        log.Should().Contain(l => l.Contains("ComponentModified") && l.Contains("GameState"));
    }

    [Fact]
    public void Serialization_RoundTrip_PreservesSnapshot()
    {
        var (world, group) = SetupGame();

        // Play a few moves.
        PlayMoves(world, group, (0, 0), (1, 1), (2, 2));

        var before = SnapshotWorld(world);

        using var stream = new MemoryStream();
        WorldSerializer.Save(world, stream);
        stream.Position = 0;

        var world2 = new World();
        WorldSerializer.Load(world2, stream);

        var after = SnapshotWorld(world2);

        _output.WriteLine("=== Before ===");
        _output.WriteLine(before);
        _output.WriteLine("=== After ===");
        _output.WriteLine(after);

        after.Should().Be(before);
    }

    // ── Helpers ───────────────────────────────────────────────────────

    private static (World, SystemGroup) SetupGame()
    {
        var world = new World();
        var group = new SystemGroup(world);
        group.Add(new WinCheckSystem());

        for (int r = 0; r < 3; r++)
            for (int c = 0; c < 3; c++)
                world.AddComponent(world.CreateEntity(), new Cell { Row = r, Col = c });

        world.SetSingleton(new GameState
        {
            CurrentPlayer = Player.X,
            Status = GameStatus.Playing,
            MoveCount = 0
        });
        world.PostChanges();

        return (world, group);
    }

    private static void PlayMoves(World world, SystemGroup group, params (int Row, int Col)[] moves)
    {
        foreach (var (row, col) in moves)
        {
            world.Commands.Enqueue(new PlaceMarkCommand { Row = row, Col = col });
            group.RunLogical();
        }
    }

    /// <summary>
    /// Produces a human-readable textual snapshot of the world state.
    /// </summary>
    private static string SnapshotWorld(World world)
    {
        var sb = new System.Text.StringBuilder();

        // Singleton: GameState.
        var state = world.ReadSingleton<GameState>();
        var statusText = state.Status switch
        {
            GameStatus.Playing => $"{(state.CurrentPlayer == Player.X ? 'X' : 'O')}'s turn, {state.MoveCount} moves",
            GameStatus.XWon => "XWon",
            GameStatus.OWon => "OWon",
            GameStatus.Draw => "Draw",
            _ => "Unknown"
        };
        sb.AppendLine($"GameState: {statusText}");

        // Board: build a 3x3 grid.
        var grid = new char?[3, 3];
        foreach (var it in world.Select<Cell, Mark>())
            grid[it.Item1.Row, it.Item1.Col] =
                it.Item2.Player == Player.X ? 'X' : 'O';

        int totalCells = 0;
        int markedCells = 0;
        for (int r = 0; r < 3; r++)
        {
            for (int c = 0; c < 3; c++)
            {
                totalCells++;
                var mark = grid[r, c];
                if (mark.HasValue)
                {
                    markedCells++;
                    sb.AppendLine($"  ({r},{c}): {mark.Value}");
                }
                else
                {
                    sb.AppendLine($"  ({r},{c}): .");
                }
            }
        }

        sb.AppendLine($"Cells: {totalCells} total, {markedCells} marked");

        return sb.ToString().TrimEnd();
    }
}