Checkers

.editorconfig

@@ -6,3 +6,6 @@ indent_style = tab
 
 # IDE0160: Convert to file-scoped namespace
 csharp_style_namespace_declarations = file_scoped:warning
+
+# IDE0042: Deconstruct variable declaration
+csharp_style_deconstructed_variable_declaration = false

.github/workflows/Checkers Build.yml

@@ -0,0 +1,24 @@
+name: Checkers Build
+on:
+  push:
+    paths:
+    - 'Projects/Checkers/**'
+    branches:
+    - main
+  pull_request:
+    paths:
+    - 'Projects/Checkers/**'
+    branches:
+    - main
+  workflow_dispatch:
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: setup dotnet
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 6.0.x
+    - name: dotnet build
+      run: dotnet build "Projects\Checkers\Checkers.csproj" --configuration Release

.vscode/launch.json

@@ -362,6 +362,16 @@
 			"console": "externalTerminal",
 			"stopAtEntry": false,
 		},
+		{
+			"name": "Checkers",
+			"type": "coreclr",
+			"request": "launch",
+			"preLaunchTask": "Build Checkers",
+			"program": "${workspaceFolder}/Projects/Checkers/bin/Debug/Checkers.dll",
+			"cwd": "${workspaceFolder}/Projects/Checkers/bin/Debug",
+			"console": "externalTerminal",
+			"stopAtEntry": false,
+		},
 		{
 			"name": "Blackjack",
 			"type": "coreclr",

.vscode/tasks.json

@@ -2,6 +2,19 @@
     "version": "2.0.0",
     "tasks":
     [
+        {
+            "label": "Build Checkers",
+            "command": "dotnet",
+            "type": "process",
+            "args":
+            [
+                "build",
+                "${workspaceFolder}/Projects/Checkers/Checkers.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary",
+            ],
+            "problemMatcher": "$msCompile",
+        },
         {
             "label": "Build Duck Hunt",
             "command": "dotnet",

Projects/Checkers/Board.cs

@@ -0,0 +1,171 @@
+namespace Checkers;
+
+public class Board
+{
+	public List<Piece> Pieces { get; }
+
+	public Piece? Aggressor { get; set; }
+
+	public Piece? this[int x, int y] =>
+		Pieces.FirstOrDefault(piece => piece.X == x && piece.Y == y);
+
+	public Board()
+	{
+		Aggressor = null;
+		Pieces = new List<Piece>
+			{
+				new() { NotationPosition ="A3", Color = Black},
+				new() { NotationPosition ="A1", Color = Black},
+				new() { NotationPosition ="B2", Color = Black},
+				new() { NotationPosition ="C3", Color = Black},
+				new() { NotationPosition ="C1", Color = Black},
+				new() { NotationPosition ="D2", Color = Black},
+				new() { NotationPosition ="E3", Color = Black},
+				new() { NotationPosition ="E1", Color = Black},
+				new() { NotationPosition ="F2", Color = Black},
+				new() { NotationPosition ="G3", Color = Black},
+				new() { NotationPosition ="G1", Color = Black},
+				new() { NotationPosition ="H2", Color = Black},
+
+				new() { NotationPosition ="A7", Color = White},
+				new() { NotationPosition ="B8", Color = White},
+				new() { NotationPosition ="B6", Color = White},
+				new() { NotationPosition ="C7", Color = White},
+				new() { NotationPosition ="D8", Color = White},
+				new() { NotationPosition ="D6", Color = White},
+				new() { NotationPosition ="E7", Color = White},
+				new() { NotationPosition ="F8", Color = White},
+				new() { NotationPosition ="F6", Color = White},
+				new() { NotationPosition ="G7", Color = White},
+				new() { NotationPosition ="H8", Color = White},
+				new() { NotationPosition ="H6", Color = White}
+			};
+	}
+
+	public static string ToPositionNotationString(int x, int y)
+	{
+		if (!IsValidPosition(x, y)) throw new ArgumentException("Not a valid position!");
+		return $"{(char)('A' + x)}{y + 1}";
+	}
+
+	public static (int X, int Y) ParsePositionNotation(string notation)
+	{
+		if (notation is null) throw new ArgumentNullException(nameof(notation));
+		notation = notation.Trim().ToUpper();
+		if (notation.Length is not 2 ||
+			notation[0] < 'A' || 'H' < notation[0] ||
+			notation[1] < '1' || '8' < notation[1])
+			throw new FormatException($@"{nameof(notation)} ""{notation}"" is not valid");
+		return (notation[0] - 'A', notation[1] - '1');
+	}
+
+	public static bool IsValidPosition(int x, int y) =>
+		0 <= x && x < 8 &&
+		0 <= y && y < 8;
+
+	public (Piece A, Piece B) GetClosestRivalPieces(PieceColor priorityColor)
+	{
+		double minDistanceSquared = double.MaxValue;
+		(Piece A, Piece B) closestRivals = (null!, null!);
+		foreach (Piece a in Pieces.Where(piece => piece.Color == priorityColor))
+		{
+			foreach (Piece b in Pieces.Where(piece => piece.Color != priorityColor))
+			{
+				(int X, int Y) vector = (a.X - b.X, a.Y - b.Y);
+				double distanceSquared = vector.X * vector.X + vector.Y * vector.Y;
+				if (distanceSquared < minDistanceSquared)
+				{
+					minDistanceSquared = distanceSquared;
+					closestRivals = (a, b);
+				}
+			}
+		}
+		return closestRivals;
+	}
+
+	public List<Move> GetPossibleMoves(PieceColor color)
+	{
+		List<Move> moves = new();
+		if (Aggressor is not null)
+		{
+			if (Aggressor.Color != color)
+			{
+				throw new Exception($"{nameof(Aggressor)} is not null && {nameof(Aggressor)}.{nameof(Aggressor.Color)} != {nameof(color)}");
+			}
+			moves.AddRange(GetPossibleMoves(Aggressor).Where(move => move.PieceToCapture is not null));
+		}
+		else
+		{
+			foreach (Piece piece in Pieces.Where(piece => piece.Color == color))
+			{
+				moves.AddRange(GetPossibleMoves(piece));
+			}
+		}
+		return moves.Any(move => move.PieceToCapture is not null)
+			? moves.Where(move => move.PieceToCapture is not null).ToList()
+			: moves;
+	}
+
+	public List<Move> GetPossibleMoves(Piece piece)
+	{
+		List<Move> moves = new();
+		ValidateDiagonalMove(-1, -1);
+		ValidateDiagonalMove(-1,  1);
+		ValidateDiagonalMove( 1, -1);
+		ValidateDiagonalMove( 1,  1);
+		return moves.Any(move => move.PieceToCapture is not null)
+			? moves.Where(move => move.PieceToCapture is not null).ToList()
+			: moves;
+
+		void ValidateDiagonalMove(int dx, int dy)
+		{
+			if (!piece.Promoted && piece.Color is Black && dy is -1) return;
+			if (!piece.Promoted && piece.Color is White && dy is 1) return;
+			(int X, int Y) target = (piece.X + dx, piece.Y + dy);
+			if (!IsValidPosition(target.X, target.Y)) return;
+			PieceColor? targetColor = this[target.X, target.Y]?.Color;
+			if (targetColor is null)
+			{
+				if (!IsValidPosition(target.X, target.Y)) return;
+				Move newMove = new(piece, target);
+				moves.Add(newMove);
+			}
+			else if (targetColor != piece.Color)
+			{
+				(int X, int Y) jump = (piece.X + 2 * dx, piece.Y + 2 * dy);
+				if (!IsValidPosition(jump.X, jump.Y)) return;
+				PieceColor? jumpColor = this[jump.X, jump.Y]?.Color;
+				if (jumpColor is not null) return;
+				Move attack = new(piece, jump, this[target.X, target.Y]);
+				moves.Add(attack);
+			}
+		}
+	}
+
+	/// <summary>Returns a <see cref="Move"/> if <paramref name="from"/>-&gt;<paramref name="to"/> is valid or null if not.</summary>
+	public Move? ValidateMove(PieceColor color, (int X, int Y) from, (int X, int Y) to)
+	{
+		Piece? piece = this[from.X, from.Y];
+		if (piece is null)
+		{
+			return null;
+		}
+		foreach (Move move in GetPossibleMoves(color))
+		{
+			if ((move.PieceToMove.X, move.PieceToMove.Y) == from && move.To == to)
+			{
+				return move;
+			}
+		}
+		return null;
+	}
+
+	public static bool IsTowards(Move move, Piece piece)
+	{
+		(int Dx, int Dy) a = (move.PieceToMove.X - piece.X, move.PieceToMove.Y - piece.Y);
+		int a_distanceSquared = a.Dx * a.Dx + a.Dy * a.Dy;
+		(int Dx, int Dy) b = (move.To.X - piece.X, move.To.Y - piece.Y);
+		int b_distanceSquared = b.Dx * b.Dx + b.Dy * b.Dy;
+		return b_distanceSquared < a_distanceSquared;
+	}
+}

Projects/Checkers/Checkers.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+	<PropertyGroup>
+		<OutputType>Exe</OutputType>
+		<TargetFramework>net6.0</TargetFramework>
+		<ImplicitUsings>disable</ImplicitUsings>
+		<Nullable>enable</Nullable>
+	</PropertyGroup>
+</Project>

Projects/Checkers/Game.cs

@@ -0,0 +1,68 @@
+namespace Checkers;
+
+public class Game
+{
+	private const int PiecesPerColor = 12;
+
+	public PieceColor Turn { get; private set; }
+	public Board Board { get; }
+	public PieceColor? Winner { get; private set; }
+	public List<Player> Players { get; }
+
+	public Game(int humanPlayerCount)
+	{
+		if (humanPlayerCount < 0 || 2 < humanPlayerCount) throw new ArgumentOutOfRangeException(nameof(humanPlayerCount));
+		Board = new Board();
+		Players = new()
+		{
+			new Player(humanPlayerCount >= 1, Black),
+			new Player(humanPlayerCount >= 2, White),
+		};
+		Turn = Black;
+		Winner = null;
+	}
+
+	public void PerformMove(Move move)
+	{
+		(move.PieceToMove.X, move.PieceToMove.Y) = move.To;
+		if ((move.PieceToMove.Color is Black && move.To.Y is 7) ||
+			(move.PieceToMove.Color is White && move.To.Y is 0))
+		{
+			move.PieceToMove.Promoted = true;
+		}
+		if (move.PieceToCapture is not null)
+		{
+			Board.Pieces.Remove(move.PieceToCapture);
+		}
+		if (move.PieceToCapture is not null &&
+			Board.GetPossibleMoves(move.PieceToMove).Any(m => m.PieceToCapture is not null))
+		{
+			Board.Aggressor = move.PieceToMove;
+		}
+		else
+		{
+			Board.Aggressor = null;
+			Turn = Turn is Black ? White : Black;
+		}
+		CheckForWinner();
+	}
+
+	public void CheckForWinner()
+	{
+		if (!Board.Pieces.Any(piece => piece.Color is Black))
+		{
+			Winner = White;
+		}
+		if (!Board.Pieces.Any(piece => piece.Color is White))
+		{
+			Winner = Black;
+		}
+		if (Winner is null && Board.GetPossibleMoves(Turn).Count is 0)
+		{
+			Winner = Turn is Black ? White : Black;
+		}
+	}
+
+	public int TakenCount(PieceColor colour) =>
+		PiecesPerColor - Board.Pieces.Count(piece => piece.Color == colour);
+}

Projects/Checkers/Move.cs

@@ -0,0 +1,17 @@
+namespace Checkers;
+
+public class Move
+{
+	public Piece PieceToMove { get; set; }
+
+	public (int X, int Y) To { get; set; }
+
+	public Piece? PieceToCapture { get; set; }
+
+	public Move(Piece pieceToMove, (int X, int Y) to, Piece? pieceToCapture = null)
+	{
+		PieceToMove = pieceToMove;
+		To = to;
+		PieceToCapture = pieceToCapture;
+	}
+}

Projects/Checkers/Piece.cs

@@ -0,0 +1,18 @@
+namespace Checkers;
+
+public class Piece
+{
+	public int X { get; set; }
+
+	public int Y { get; set; }
+
+	public string NotationPosition
+	{
+		get => Board.ToPositionNotationString(X, Y);
+		set => (X, Y) = Board.ParsePositionNotation(value);
+	}
+
+	public PieceColor Color { get; set; }
+
+	public bool Promoted { get; set; }
+}

Projects/Checkers/PieceColor.cs

@@ -0,0 +1,7 @@
+namespace Checkers;
+
+public enum PieceColor
+{
+	Black = 1,
+	White = 2,
+}

Projects/Checkers/Player.cs

@@ -0,0 +1,13 @@
+namespace Checkers;
+
+public class Player
+{
+	public bool IsHuman { get; }
+	public PieceColor Color { get; }
+
+	public Player(bool isHuman, PieceColor color)
+	{
+		IsHuman = isHuman;
+		Color = color;
+	}
+}