Simple command line hangman game

hangman.go

package main

import (
	"flag"
	"fmt"
	"io/ioutil"
	"math/rand"
	"strings"
	"time"
)

var wordFile = flag.String("word_file", "", "Word file.")

const NUM_GUESSES = 10

func main() {
	flag.Parse()

	if *wordFile == "" {
		fmt.Println("Please provide a word file. For example:")
		fmt.Println("  go hangman.go --word_file /usr/share/dict/words")
		return
	}

	game := NewGame(findWord(*wordFile))
	game.Start()
}

func NewGame(target string) GameState {
	return GameState{[]byte(target), NUM_GUESSES, map[byte]bool{}}
}

type GameState struct {
	target           []byte
	remainingGuesses int
	guesses          map[byte]bool
}

func (game *GameState) Start() {
	fmt.Printf("Welcome, here's your word: %s\n", game.DisplayWord())

	for {
		var guess string
		fmt.Printf("Enter a character: ")
		_, err := fmt.Scanln(&guess)
		if err != nil || len(guess) != 1 {
			fmt.Printf("That wasn't a valid guess, try entering just one character.\n")
		} else {
			game.MakeGuess(guess[0])
			time.Sleep(500 * time.Millisecond)
			if game.IsWin() {
				fmt.Printf("Congratulations, you win! The word was %s\n", game.target)
				return
			} else if game.remainingGuesses == 0 {
				fmt.Printf("Boo, you loose. Here's the answer: %s\n", game.target)
				return
			} else {
				fmt.Printf("%s, %d guesses remaining.\n", game.DisplayWord(), game.remainingGuesses)
				time.Sleep(250 * time.Millisecond)
			}
		}
	}
}

func (game *GameState) IsWin() bool {
	for _, c := range game.target {
		if _, exists := game.guesses[c]; !exists {
			return false
		}
	}
	return true
}

func (game *GameState) IsCorrectGuess(guess byte) bool {
	for _, c := range game.target {
		if c == guess {
			return true
		}
	}
	return false
}

func (game *GameState) MakeGuess(guess byte) {
	if _, exists := game.guesses[guess]; !exists {
		correct := game.IsCorrectGuess(guess)
		game.guesses[guess] = correct
		if !correct {
			game.remainingGuesses--
		}
	}
}

func (game *GameState) DisplayWord() string {
	s := make([]byte, len(game.target)*2)
	for i, c := range game.target {
		if _, exists := game.guesses[c]; exists {
			s[i*2] = c
		} else {
			s[i*2] = '_'
		}
		s[i*2+1] = ' '
	}
	return string(s)
}

func findWord(filename string) string {
	bytes, err := ioutil.ReadFile(filename)
	if err != nil {
		panic(err)
	}
	lines := strings.Split(string(bytes), "\n")
	rand.Seed(time.Now().Unix())
	return strings.ToLower(strings.TrimSpace(lines[rand.Intn(len(lines))]))
}

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