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

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

namespace Game.TicTacToe.Tests;

public class GameFlowTests
{
    [Fact]
    public void NewGame_HasEmptyBoard()
    {
        var (world, _) = SetupGame();

        var query = world.Query().With<Cell>().Without<Mark>().Build();
        var emptyCount = 0;
        world.ForEach(query, (Entity e, ref Cell cell) => emptyCount++);

        emptyCount.Should().Be(9);
    }

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

        world.Commands.Enqueue(new PlaceMarkCommand { Row = 0, Col = 0 });
        group.RunLogical();

        var query = world.Query().With<Cell>().With<Mark>().Build();
        var markedCount = 0;
        world.ForEach(query, (Entity e, ref Cell cell, ref Mark mark) =>
        {
            markedCount++;
            cell.Row.Should().Be(0);
            cell.Col.Should().Be(0);
            mark.Player.Should().Be(Player.X);
        });

        markedCount.Should().Be(1);
    }

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

        world.Commands.Enqueue(new PlaceMarkCommand { Row = 0, Col = 0 }); // X
        group.RunLogical();
        world.ReadSingleton<GameState>().CurrentPlayer.Should().Be(Player.O);

        world.Commands.Enqueue(new PlaceMarkCommand { Row = 1, Col = 0 }); // O
        group.RunLogical();
        world.ReadSingleton<GameState>().CurrentPlayer.Should().Be(Player.X);
    }

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

        world.Commands.Enqueue(new PlaceMarkCommand { Row = 0, Col = 0 }); // X
        group.RunLogical();
        world.Commands.Enqueue(new PlaceMarkCommand { Row = 0, Col = 0 }); // O tries same cell
        group.RunLogical();

        // Only one mark should exist at (0,0), and it should still be X.
        var query = world.Query().With<Cell>().With<Mark>().Build();
        var marks = new List<(int Row, int Col, Player Player)>();
        world.ForEach(query, (Entity e, ref Cell cell, ref Mark mark) =>
        {
            marks.Add((cell.Row, cell.Col, mark.Player));
        });

        marks.Should().ContainSingle()
            .Which.Should().Be((0, 0, Player.X));
    }

    [Fact]
    public void XWins_Row()
    {
        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));

        world.ReadSingleton<GameState>().Status.Should().Be(GameStatus.XWon);
    }

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

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

        world.ReadSingleton<GameState>().Status.Should().Be(GameStatus.OWon);
    }

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

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

        world.ReadSingleton<GameState>().Status.Should().Be(GameStatus.XWon);
    }

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

        // Fill all 9 cells without a winner.
        // X: (0,0) (0,2) (1,0) (2,1) (2,2)
        // O: (0,1) (1,1) (1,2) (2,0)
        PlayMoves(world, group,
            (0, 0), (0, 1), (0, 2),
            (1, 1), (1, 0), (1, 2),
            (2, 1), (2, 0), (2, 2));

        world.ReadSingleton<GameState>().Status.Should().Be(GameStatus.Draw);
    }

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

        // X wins.
        PlayMoves(world, group, (0, 0), (1, 0), (0, 1), (1, 1), (0, 2));

        world.ReadSingleton<GameState>().Status.Should().Be(GameStatus.XWon);

        // Try to place another mark — should be ignored.
        var moveCountBefore = world.ReadSingleton<GameState>().MoveCount;
        world.Commands.Enqueue(new PlaceMarkCommand { Row = 2, Col = 2 });
        group.RunLogical();

        world.ReadSingleton<GameState>().MoveCount.Should().Be(moveCountBefore);
    }

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

        // Play a few moves.
        world.Commands.Enqueue(new PlaceMarkCommand { Row = 0, Col = 0 });
        group.RunLogical();
        world.Commands.Enqueue(new PlaceMarkCommand { Row = 1, Col = 0 });
        group.RunLogical();

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

        // Load into a new world.
        var world2 = new World();
        WorldSerializer.Load(world2, stream);

        // Verify state.
        var state = world2.ReadSingleton<GameState>();
        state.CurrentPlayer.Should().Be(Player.X);
        state.MoveCount.Should().Be(2);

        var query = world2.Query().With<Cell>().With<Mark>().Build();
        var marks = new List<(int Row, int Col, Player Player)>();
        world2.ForEach(query, (Entity e, ref Cell cell, ref Mark mark) =>
        {
            marks.Add((cell.Row, cell.Col, mark.Player));
        });

        marks.Should().BeEquivalentTo([(0, 0, Player.X), (1, 0, Player.O)]);
    }

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

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

        // Create the 9 cells.
        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();
        }
    }
}