review me

src/Game.ts

@@ -0,0 +1,103 @@
+export class Game {
+    private _lastSymbol: string = ' ';
+    private _board: Board = new Board();
+
+    public Play(symbol: string, x: number, y: number) : void {
+        //if first move
+        if (this._lastSymbol == ' ') {
+            //if player is X
+            if (symbol == 'O') {
+                throw new Error("Invalid first player");
+            }
+        }
+        //if not first move but player repeated
+        else if (symbol == this._lastSymbol) {
+            throw new Error("Invalid next player");
+        }
+        //if not first move but play on an already played tile
+        else if (this._board.TileAt(x, y).Symbol != ' ') {
+            throw new Error("Invalid position");
+        }
+
+        // update game state
+        this._lastSymbol = symbol;
+        this._board.AddTileAt(symbol, x, y);
+    }
+
+    public Winner() : string {
+        //if the positions in first row are taken
+        if (this._board.TileAt(0, 0)!.Symbol != ' ' &&
+                this._board.TileAt(0, 1)!.Symbol != ' ' &&
+                this._board.TileAt(0, 2)!.Symbol != ' ') {
+            //if first row is full with same symbol
+            if (this._board.TileAt(0, 0)!.Symbol ==
+                    this._board.TileAt(0, 1)!.Symbol &&
+                    this._board.TileAt(0, 2)!.Symbol == this._board.TileAt(0, 1)!.Symbol) {
+                return this._board.TileAt(0, 0)!.Symbol;
+            }
+        }
+
+        //if the positions in first row are taken
+        if (this._board.TileAt(1, 0)!.Symbol != ' ' &&
+                this._board.TileAt(1, 1)!.Symbol != ' ' &&
+                this._board.TileAt(1, 2)!.Symbol != ' ') {
+            //if middle row is full with same symbol
+            if (this._board.TileAt(1, 0)!.Symbol ==
+                    this._board.TileAt(1, 1)!.Symbol &&
+                    this._board.TileAt(1, 2)!.Symbol ==
+                            this._board.TileAt(1, 1)!.Symbol) {
+                return this._board.TileAt(1, 0)!.Symbol;
+            }
+        }
+
+        //if the positions in first row are taken
+        if (this._board.TileAt(2, 0)!.Symbol != ' ' &&
+                this._board.TileAt(2, 1)!.Symbol != ' ' &&
+                this._board.TileAt(2, 2)!.Symbol != ' ') {
+            //if middle row is full with same symbol
+            if (this._board.TileAt(2, 0)!.Symbol ==
+                    this._board.TileAt(2, 1)!.Symbol &&
+                    this._board.TileAt(2, 2)!.Symbol ==
+                            this._board.TileAt(2, 1)!.Symbol) {
+                return this._board.TileAt(2, 0)!.Symbol;
+            }
+        }
+
+        return ' ';
+    }
+}
+
+interface Tile
+{
+    X: number;
+    Y: number;
+    Symbol: string;
+}
+
+class Board
+{
+    private _plays : Tile[] = [];
+
+    constructor()
+    {
+        for (let i = 0; i < 3; i++)
+        {
+            for (let j = 0; j < 3; j++)
+            {
+                const tile : Tile = {X :i, Y:j, Symbol:" "};
+                this._plays.push(tile);
+            }
+        }
+    }
+
+    public TileAt(x:  number, y: number): Tile {
+        return this._plays.find((t:Tile) => t.X == x && t.Y == y)!
+    }
+
+    public AddTileAt(symbol: string, x: number, y: number) : void
+    {
+        const tile : Tile = {X :x, Y:y, Symbol:symbol};
+
+        this._plays.find((t:Tile) => t.X == x && t.Y == y)!.Symbol = symbol;
+    }
+}