minesweeper-codex/tests/Minesweeper.Tests/BoardTests.cs

using Minesweeper.Game;
using Xunit;

namespace Minesweeper.Tests;

public class BoardTests
{
    private static readonly string[] s_floodLayout =
    [
        ".....",
        ".....",
        ".....",
        ".....",
        "...x.",
    ];

    private static readonly string[] s_twinMineLayout =
    [
        "x.x",
        "...",
        "...",
    ];

    [Theory]
    [InlineData(0, 5, 1)]
    [InlineData(5, 0, 1)]
    [InlineData(3, 3, -1)]
    [InlineData(3, 3, 9)]
    public void ConstructorRejectsImpossibleBoards(int width, int height, int mines) =>
        Assert.ThrowsAny<ArgumentOutOfRangeException>(() => new Board(width, height, mines));

    [Fact]
    public void FirstClickKeepsTheChosenSquareClear()
    {
        for (var seed = 0; seed < 50; seed++)
        {
            var board = new Board(9, 9, 10);
            board.PlantMines(new CellRef(4, 4), reserveSafeZone: false, new Random(seed));

            Assert.False(board.At(4, 4).IsMine);
            Assert.Equal(10, board.MineCount);
            Assert.Equal(10, board.MineCells().Count());
        }
    }

    [Fact]
    public void FirstClickCanAlsoKeepItsNeighborhoodClear()
    {
        for (var seed = 0; seed < 50; seed++)
        {
            var board = new Board(9, 9, 10);
            board.PlantMines(new CellRef(4, 4), reserveSafeZone: true, new Random(seed));

            Assert.Equal(0, board.MineCells().Count(m => m == new CellRef(4, 4) || board.NeighborsOf(4, 4).Contains(m)));
        }
    }

    [Fact]
    public void PlantingTwiceThrows()
    {
        var board = TestBoards.Create(s_floodLayout);
        Assert.Throws<InvalidOperationException>(() => board.PlantMines([]));
        Assert.Throws<InvalidOperationException>(() => board.PlantMines(new CellRef(0, 0), true, new Random(1)));
    }

    [Fact]
    public void NumbersComeFromTheMineLayout()
    {
        var board = TestBoards.Create(s_floodLayout);

        Assert.True(board.At(3, 4).IsMine);
        Assert.Equal(0, board.At(0, 0).AdjacentMines);
        Assert.Equal(1, board.At(2, 3).AdjacentMines);
        Assert.Equal(1, board.At(4, 4).AdjacentMines);
        Assert.Equal(1, board.MineCount);
    }

    [Theory]
    [InlineData(0, 0, 3)]
    [InlineData(2, 0, 5)]
    [InlineData(2, 2, 8)]
    public void NeighborCountsRespectTheEdges(int x, int y, int expected)
    {
        var board = new Board(5, 5, 0);
        Assert.Equal(expected, board.NeighborsOf(x, y).Count());
    }

    [Fact]
    public void OpeningABlankSquareFloodsUntilTheNumbers()
    {
        var board = TestBoards.Create(s_floodLayout);
        var result = board.Open(new CellRef(0, 0));

        Assert.False(result.HitMine);
        Assert.Equal(23, result.Opened.Count);
        Assert.False(board.At(3, 4).IsRevealed);
        Assert.True(board.At(2, 3).IsRevealed);
        Assert.Equal(23, Revealed(board));

        // (4,4) only touches other numbers and the mine, so a flood can never reach it.
        Assert.False(board.At(4, 4).IsRevealed);
    }

    [Fact]
    public void FlagsHoldBackTheFloodFill()
    {
        var board = TestBoards.Create(s_floodLayout);
        board.At(0, 2).State = CellState.Flagged;

        var result = board.Open(new CellRef(0, 0));

        Assert.Equal(22, result.Opened.Count);
        Assert.True(board.At(0, 2).IsFlagged);
    }

    [Fact]
    public void OpeningANumberedSquareRevealsOnlyIt()
    {
        var board = TestBoards.Create("x..", "...", "...");
        var result = board.Open(new CellRef(1, 0));

        Assert.Single(result.Opened);
        Assert.True(board.At(1, 0).IsRevealed);
        Assert.False(board.At(2, 2).IsRevealed);
    }

    [Fact]
    public void OpeningAMineReportsTheBoom()
    {
        var board = TestBoards.Create(s_floodLayout);
        var result = board.Open(new CellRef(3, 4));

        Assert.True(result.HitMine);
        Assert.Equal(new CellRef(3, 4), result.Boom!.Value);
        Assert.True(board.At(3, 4).IsRevealed);
    }

    [Fact]
    public void ChordOpensTheRestWhenTheFlagsMatch()
    {
        var board = TestBoards.Create(s_twinMineLayout);
        board.Open(new CellRef(1, 0));
        board.At(0, 0).State = CellState.Flagged;
        board.At(2, 0).State = CellState.Flagged;

        var result = board.Chord(new CellRef(1, 0));

        Assert.False(result.HitMine);
        Assert.Equal(3, result.Opened.Count);
        Assert.True(board.At(0, 1).IsRevealed);
        Assert.True(board.At(1, 1).IsRevealed);
        Assert.True(board.At(2, 1).IsRevealed);
    }

    [Theory]
    [InlineData(1)]
    [InlineData(3)]
    public void ChordWithTheWrongFlagCountJustPops(int flags)
    {
        var board = TestBoards.Create(s_twinMineLayout);
        board.Open(new CellRef(1, 0));
        board.At(0, 0).State = CellState.Flagged;
        if (flags > 1)
            board.At(0, 1).State = CellState.Flagged;
        if (flags > 2)
            board.At(1, 1).State = CellState.Flagged;

        var result = board.Chord(new CellRef(1, 0));

        Assert.False(result.AnyOpened);
        Assert.False(result.HitMine);
        Assert.Equal(1, Revealed(board));
    }

    [Fact]
    public void ChordCanStepOnAnUnflaggedMine()
    {
        var board = TestBoards.Create(s_twinMineLayout);
        board.Open(new CellRef(1, 0));
        board.At(0, 0).State = CellState.Flagged;
        board.At(0, 1).State = CellState.Flagged;

        var result = board.Chord(new CellRef(1, 0));

        Assert.True(result.HitMine);
        Assert.Equal(new CellRef(2, 0), result.Boom!.Value);
    }

    [Fact]
    public void ChordIgnoresHiddenSquares()
    {
        var board = TestBoards.Create(s_twinMineLayout);
        Assert.False(board.Chord(new CellRef(1, 1)).AnyOpened);
    }

    [Fact]
    public void TinyBoardsLoseMinesTheyCannotFit()
    {
        var board = new Board(2, 2, 3);
        board.PlantMines(new CellRef(0, 0), reserveSafeZone: true, new Random(3));

        Assert.Equal(0, board.MineCount);
        Assert.Empty(board.MineCells());
    }

    [Fact]
    public void OutOfRangeSquaresThrow()
    {
        var board = new Board(3, 3, 1);
        Assert.Throws<ArgumentOutOfRangeException>(() => board.At(3, 0));
        Assert.False(board.InBounds(-1, 2));
        Assert.True(board.InBounds(2, 2));
    }

    private static int Revealed(Board board) => board.AllCells().Count(reference => board.At(reference).IsRevealed);
}