Add Tic-tac-toe game command and tests

Author: chrisreddington

cmd/root.go

@@ -17,4 +17,5 @@ func Execute() error {
 func init() {
 	rootCmd.AddCommand(whoamiCmd)
 	rootCmd.AddCommand(cointossCmd)
+	rootCmd.AddCommand(tictactoeCmd)
 }

cmd/tictactoe.go

@@ -0,0 +1,48 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/chrisreddington/gh-game/internal/tictactoe"
+	userPrompt "github.com/cli/go-gh/v2/pkg/prompter"
+	"github.com/spf13/cobra"
+)
+
+var tictactoeCmd = &cobra.Command{
+	Use:   "tictactoe",
+	Short: "Play Tic-tac-toe",
+	Long:  `Start a game of Tic-tac-toe where X and O take turns to play.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		game := tictactoe.NewGame()
+		prompter := userPrompt.New(os.Stdin, os.Stdout, os.Stderr)
+
+		for {
+			fmt.Println(game)
+			fmt.Printf("Player %s's turn\n", game.CurrentPlayer)
+
+			row, col, err := tictactoe.GetPlayerMove(prompter, game)
+			if err != nil {
+				fmt.Printf("Error getting move: %v\n", err)
+				return
+			}
+
+			if err := game.MakeMove(row, col); err != nil {
+				fmt.Printf("Invalid move: %v\n", err)
+				continue
+			}
+
+			if winner := game.GetWinner(); winner != "" {
+				fmt.Println(game)
+				fmt.Printf("Player %s wins!\n", winner)
+				return
+			}
+
+			if game.IsBoardFull() {
+				fmt.Println(game)
+				fmt.Println("It's a draw!")
+				return
+			}
+		}
+	},
+}

internal/tictactoe/tictactoe.go

@@ -0,0 +1,208 @@
+// Package tictactoe implements a classic Tic-tac-toe game where two players
+// take turns marking spaces on a 3x3 grid. Players alternate placing X's and O's
+// on the board until either one player wins by placing three marks in a row,
+// column, or diagonal, or the game ends in a draw when the board is full.
+package tictactoe
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Prompter defines an interface for getting user input
+type Prompter interface {
+	Select(prompt, defaultValue string, options []string) (int, error)
+}
+
+// Board represents a 3x3 Tic-tac-toe game board.
+// Empty squares are represented by empty strings,
+// and played squares contain either "X" or "O".
+type Board [3][3]string
+
+// Game represents the current state of a Tic-tac-toe game.
+type Game struct {
+	board         Board  // The game board storing player moves ("X" or "O", or empty for unplayed)
+	CurrentPlayer string // CurrentPlayer indicates whose turn it is ("X" or "O")
+}
+
+// NewGame creates and initializes a new Tic-tac-toe game with an empty board.
+// Setting as X always plays first.
+func NewGame() *Game {
+	return &Game{
+		board:         Board{},
+		CurrentPlayer: "X",
+	}
+}
+
+// MakeMove attempts to place the current player's mark at the specified position.
+// The position is specified using zero-based indices for row and column.
+// Returns an error if:
+// - The position is out of bounds (not between 0 and 2)
+// - The position is already occupied by a player's mark
+func (g *Game) MakeMove(rowIndex, columnIndex int) error {
+	if rowIndex < 0 || rowIndex > 2 || columnIndex < 0 || columnIndex > 2 {
+		return errors.New("invalid position: must be between 0 and 2")
+	}
+
+	if g.board[rowIndex][columnIndex] != "" {
+		return errors.New("position already taken")
+	}
+
+	g.board[rowIndex][columnIndex] = g.CurrentPlayer
+	g.CurrentPlayer = switchPlayer(g.CurrentPlayer)
+	return nil
+}
+
+// GetWinner checks if there is a winner by examining all possible winning combinations:
+// - Three rows
+// - Three columns
+// - Two diagonals
+// Returns the winning player's mark ("X" or "O"), or an empty string if there's no winner.
+func (g *Game) GetWinner() string {
+	// Check rows for a winner
+	for rowIndex := 0; rowIndex < 3; rowIndex++ {
+		if g.board[rowIndex][0] != "" &&
+			g.board[rowIndex][0] == g.board[rowIndex][1] &&
+			g.board[rowIndex][1] == g.board[rowIndex][2] {
+			return g.board[rowIndex][0]
+		}
+	}
+
+	// Check columns for a winner
+	for columnIndex := 0; columnIndex < 3; columnIndex++ {
+		if g.board[0][columnIndex] != "" &&
+			g.board[0][columnIndex] == g.board[1][columnIndex] &&
+			g.board[1][columnIndex] == g.board[2][columnIndex] {
+			return g.board[0][columnIndex]
+		}
+	}
+
+	// Check main diagonal (top-left to bottom-right)
+	if g.board[0][0] != "" &&
+		g.board[0][0] == g.board[1][1] &&
+		g.board[1][1] == g.board[2][2] {
+		return g.board[0][0]
+	}
+
+	// Check secondary diagonal (top-right to bottom-left)
+	if g.board[0][2] != "" &&
+		g.board[0][2] == g.board[1][1] &&
+		g.board[1][1] == g.board[2][0] {
+		return g.board[0][2]
+	}
+
+	return ""
+}
+
+// IsBoardFull determines if all positions on the board have been played.
+// Returns true if no empty positions remain, false otherwise.
+func (g *Game) IsBoardFull() bool {
+	for rowIndex := 0; rowIndex < 3; rowIndex++ {
+		for columnIndex := 0; columnIndex < 3; columnIndex++ {
+			if g.board[rowIndex][columnIndex] == "" {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// String returns a formatted string representation of the current board state.
+// Empty squares are shown as numbers 1-9 for position selection, making it
+// easier for players to choose their moves. Played squares show the player's mark.
+// The board is displayed with column separators (|) and row separators (-).
+func (g *Game) String() string {
+	result := "\n"
+	position := 1
+	for rowIndex := 0; rowIndex < 3; rowIndex++ {
+		for columnIndex := 0; columnIndex < 3; columnIndex++ {
+			// Add leading space for first column
+			if columnIndex == 0 {
+				result += " "
+			}
+
+			// Show position number for empty squares, otherwise show the player's mark
+			if g.board[rowIndex][columnIndex] == "" {
+				result += fmt.Sprintf("%d", position)
+			} else {
+				result += g.board[rowIndex][columnIndex]
+			}
+
+			// Add column separators except for the last column
+			if columnIndex < 2 {
+				result += " | "
+			}
+			position++
+		}
+		result += "\n"
+
+		// Add row separators except for the last row
+		if rowIndex < 2 {
+			result += "---+---+---\n"
+		}
+	}
+	return result
+}
+
+// switchPlayer determines the next player's turn.
+// Following traditional Tic-tac-toe rules, players alternate between X and O.
+func switchPlayer(currentPlayer string) string {
+	if currentPlayer == "X" {
+		return "O"
+	}
+	return "X"
+}
+
+// positionToRowCol converts a one-based position (1-9) to zero-based row and column indices.
+// The board positions are mapped as follows:
+// 1 2 3
+// 4 5 6
+// 7 8 9
+func positionToRowCol(position int) (rowIndex, columnIndex int) {
+	position-- // Convert to 0-based index
+	return position / 3, position % 3
+}
+
+// getAvailablePositions returns a slice of strings representing unoccupied positions.
+// The positions are numbered 1-9 (one-based) to match the display format.
+func (g *Game) getAvailablePositions() []string {
+	var availablePositions []string
+	for position := 1; position <= 9; position++ {
+		rowIndex, columnIndex := positionToRowCol(position)
+		if g.board[rowIndex][columnIndex] == "" {
+			availablePositions = append(availablePositions, fmt.Sprintf("%d", position))
+		}
+	}
+	return availablePositions
+}
+
+// GetPlayerMove prompts the user to select a valid move and returns the chosen
+// row and column indices. It uses the provided Prompter interface to get user input.
+// Returns an error if:
+// - No valid moves are available (board is full)
+// - User input is invalid
+// - Selected position is invalid
+func GetPlayerMove(prompter Prompter, game *Game) (rowIndex, columnIndex int, err error) {
+	availablePositions := game.getAvailablePositions()
+	if len(availablePositions) == 0 {
+		return 0, 0, errors.New("no available moves")
+	}
+
+	posIndex, err := prompter.Select("Select position (1-9):", availablePositions[0], availablePositions)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	if posIndex < 0 || posIndex >= len(availablePositions) {
+		return 0, 0, fmt.Errorf("invalid position selection: %d", posIndex)
+	}
+
+	var position int
+	_, err = fmt.Sscanf(availablePositions[posIndex], "%d", &position)
+	if err != nil {
+		return 0, 0, fmt.Errorf("invalid position value: %v", err)
+	}
+
+	rowIndex, columnIndex = positionToRowCol(position)
+	return rowIndex, columnIndex, nil
+}