Initial commit

`Tokenizer` can _just barely_ parse a basic, well-formed move list.

Initially, I wanted to provide the movetext as a `Stream` rather than a
string, the idea being that it could be processed as it was being read
from a file without having to read the entire file into memory first. I
had difficulties with the stream being unreadable in
`Tokenizer.ParseMoves()`, so I switched to a string in order to get the
actual parsing logic down first.

Because of the `yield return` strategy, the debug console output
includes all of the expected halfmoves multiple times in various orders.
After running a test, generally the full, in-order list seems to exist
at the bottom of the output.

6 files changed, 155 insertions, 0 deletions

diff --git a/DotnetPgn/DotnetPgn.csproj b/DotnetPgn/DotnetPgn.csproj
new file mode 100644
index 0000000..563e6f9
--- /dev/null
+++ b/DotnetPgn/DotnetPgn.csproj
@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">

+

+  <PropertyGroup>

+    <TargetFramework>net5.0</TargetFramework>

+  </PropertyGroup>

+

+</Project>

diff --git a/DotnetPgn/Models/Enums.cs b/DotnetPgn/Models/Enums.cs
new file mode 100644
index 0000000..893f2fa
--- /dev/null
+++ b/DotnetPgn/Models/Enums.cs
@@ -0,0 +1,18 @@
+namespace DotnetPgn.Models
+{
+    public enum Piece
+    {
+        Pawn,
+        Knight,
+        Bishop,
+        Rook,
+        Queen,
+        King,
+    }
+
+    public enum Player
+    {
+        White,
+        Black,
+    }
+}
\ No newline at end of file
diff --git a/DotnetPgn/Models/HalfMove.cs b/DotnetPgn/Models/HalfMove.cs
new file mode 100644
index 0000000..b94d77d
--- /dev/null
+++ b/DotnetPgn/Models/HalfMove.cs
@@ -0,0 +1,11 @@
+namespace DotnetPgn.Models
+{
+    public record HalfMove
+    {
+        public int MoveNumber {get; init;}
+        public Player Player { get; init; }
+        public Piece Piece { get; init; }
+        public Square SourceSquare { get; init; }
+        public Square TargetSquare { get; init; }
+    }
+}
\ No newline at end of file
diff --git a/DotnetPgn/Models/Square.cs b/DotnetPgn/Models/Square.cs
new file mode 100644
index 0000000..a3910d3
--- /dev/null
+++ b/DotnetPgn/Models/Square.cs
@@ -0,0 +1,22 @@
+using System;
+
+namespace DotnetPgn.Models
+{
+    public record Square
+    {
+        public char Rank { get; }
+        public int File { get; }
+
+        public Square(char rank, int file)
+        {
+            if (rank < 'a' || rank > 'h')
+                throw new ArgumentException($"Invalid rank '{rank}'.");
+
+            if (file < 1 || file > 8)
+                throw new ArgumentException($"Invalid file '{file}'.");
+
+            Rank = rank;
+            File = file;
+        }
+    }
+}
\ No newline at end of file
diff --git a/DotnetPgn/PieceParser.cs b/DotnetPgn/PieceParser.cs
new file mode 100644
index 0000000..5ea9402
--- /dev/null
+++ b/DotnetPgn/PieceParser.cs
@@ -0,0 +1,22 @@
+using System;

+using DotnetPgn.Models;

+

+namespace DotnetPgn

+{

+    public static class PieceParser

+    {

+        public static Piece ParsePiece(string sanPiece)

+        {

+            return sanPiece switch

+            {

+                "P" or "p" or "" => Piece.Pawn,

+                "N" or "n" => Piece.Knight,

+                "B" or "b" => Piece.Bishop,

+                "R" or "r" => Piece.Rook,

+                "Q" or "q" => Piece.Queen,

+                "K" or "k" => Piece.King,

+                _ => throw new ArgumentException($"'{sanPiece} is not a valid piece.'"),

+            };

+        }

+    }

+}

diff --git a/DotnetPgn/Tokenizer.cs b/DotnetPgn/Tokenizer.cs
new file mode 100644
index 0000000..9f779cb
--- /dev/null
+++ b/DotnetPgn/Tokenizer.cs
@@ -0,0 +1,75 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using System.Text.RegularExpressions;
+using DotnetPgn.Models;
+
+namespace DotnetPgn
+{
+    public static class Tokenizer
+    {
+        private static readonly Regex s_halfMoveRegex =
+            new(@"([KQRBNP]?)([a-h]?[1-8]?)(x?)([a-h][1-8])([+#]?)");
+
+        public static IEnumerable<HalfMove> ParseMoves(string moveText)
+        {
+            StringBuilder currToken = new();
+            char[] moveTextChars = moveText.ToCharArray();
+            int moveNumber = 1;
+            Player currPlayer = Player.White;
+
+            for (int i = 0; i < moveTextChars.Length; i++)
+            {
+                char nextChar = moveTextChars[i];
+
+                if (nextChar is ' ' or '\t' or '\n' or '\r')
+                {
+                    // We should have either a move number or a complete halfmove.
+                    string token = currToken.ToString();
+                    currToken.Clear();
+                    Match match = s_halfMoveRegex.Match(token);
+
+                    if (!match.Success)
+                    {
+                        Console.WriteLine($"Unrecognized token: `{token}`");
+                        Console.WriteLine();
+                        continue;
+                    }
+
+                    Console.WriteLine($"Recognized token: {token}");
+                    Console.WriteLine($"Matching groups: ({match.Groups[1].Value})" +
+                        $"({match.Groups[2].Value})({match.Groups[3].Value})({match.Groups[4].Value})" +
+                        $"({match.Groups[5].Value})");
+
+                    var move = new HalfMove
+                    {
+                        MoveNumber = moveNumber,
+                        Player = currPlayer,
+                        Piece = PieceParser.ParsePiece(match.Groups[1].Value),
+                        TargetSquare = new Square(match.Groups[4].Value[0], Convert.ToInt32(Char.GetNumericValue(match.Groups[4].Value[1]))),
+                    };
+
+                    Console.WriteLine($"Halfmove: {move.MoveNumber}. {move.Player} {move.Piece} from {move.SourceSquare} to {move.TargetSquare}");
+                    Console.WriteLine();
+
+                    if (currPlayer == Player.White)
+                    {
+                        currPlayer = Player.Black;
+                    }
+                    else
+                    {
+                        currPlayer = Player.White;
+                        moveNumber++;
+                    }
+
+                    yield return move;
+                }
+                else
+                {
+                    currToken.Append(nextChar);
+                }
+            }
+        }
+    }
+}
\ No newline at end of file