rx-hangman.ts

import { Observable, BehaviorSubject, Subject } from 'rxjs'
import { withLatestFrom } from 'rxjs/operators'
import { deepEqual } from 'assert'

interface IGameState {
  status: GameStatus
  selectedLetters: string[]
  lifeLeft: number
  secretWordLength: number
  knownSecretWord: string
}

enum GameStatus {
  IN_PROGRESS = 'in-progress',
  WON = 'won',
  LOSE = 'lose',
}

function reactiveHangman(secretWord: string, letter$: Observable<string>) {
  const initGameState = getInitGameState(secretWord, 7)
  const gameState$ = new BehaviorSubject(initGameState)
  const letterWithGameState$ = letter$.pipe(withLatestFrom(gameState$))
  letterWithGameState$.subscribe(([letter, gameState]) => {
    const nextGameState = getNextGameState(gameState, secretWord, letter)
    gameState$.next(nextGameState)
    const { status } = nextGameState
    const winOrLose = status === GameStatus.WON || status === GameStatus.LOSE
    if (winOrLose) {
      gameState$.complete()
    }
  })
  return gameState$.asObservable()
}

function getInitGameState(secretWord: string, lives: number) {
  const secretWordLength = secretWord.length
  const initGameState: IGameState = {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: [],
    lifeLeft: lives,
    secretWordLength: secretWord.length,
    knownSecretWord: '_'.repeat(secretWordLength),
  }
  return initGameState
}

function fillCorrectLetters(word: string, filledWord: string, letter: string) {
  const newFilledWord = [...word].reduce(
    (filedWord, char, idx) => {
      if (char === letter) {
        filedWord[idx] = char
      }
      return filedWord
    },
    [...filledWord]
  )
  return newFilledWord.join('')
}

function isWin(knowSecretWord: string) {
  return [...knowSecretWord].every(char => char !== '_')
}

function getNextGameState(
  gameState: IGameState,
  secretWord: string,
  letter: string
): IGameState {
  const {
    selectedLetters,
    lifeLeft,
    secretWordLength,
    knownSecretWord,
  } = gameState
  const newSelectedLetters = selectedLetters.concat(letter)
  const correctLetter = secretWord.includes(letter)
  const newLifeLeft = correctLetter ? lifeLeft : lifeLeft - 1
  const newKnownSecretWord = fillCorrectLetters(
    secretWord,
    knownSecretWord,
    letter
  )
  const win = isWin(newKnownSecretWord)
  const lose = newLifeLeft === 0
  const newStatus = win
    ? GameStatus.WON
    : lose
      ? GameStatus.LOSE
      : GameStatus.IN_PROGRESS
  return {
    status: newStatus,
    selectedLetters: newSelectedLetters,
    lifeLeft: newLifeLeft,
    secretWordLength,
    knownSecretWord: newKnownSecretWord,
  }
}

// Test

function test(secretWord: string, letters: string, expected: IGameState[]) {
  const letterSubject = new Subject<string>()
  const letter$ = letterSubject.asObservable()
  const gameState$ = reactiveHangman(secretWord, letter$)
  const actual: IGameState[] = []
  gameState$.subscribe(
    gameState => actual.push(gameState),
    () => {},
    () => {
      deepEqual(actual, expected)
    }
  )
  ;[...letters].forEach(letter => letterSubject.next(letter))
}

// Test case 1

const expected1: IGameState[] = [
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: [],
    lifeLeft: 7,
    secretWordLength: 7,
    knownSecretWord: '_______',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b'],
    lifeLeft: 7,
    secretWordLength: 7,
    knownSecretWord: 'b__b___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'b__b___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'i'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'bi_b___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'i', 'g'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'bigb___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'i', 'g', 'a'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'bigb_a_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'i', 'g', 'a', 'e'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'bigbea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'i', 'g', 'a', 'e', 'y'],
    lifeLeft: 5,
    secretWordLength: 7,
    knownSecretWord: 'bigbea_',
  },
  {
    status: GameStatus.WON,
    selectedLetters: ['b', 'o', 'i', 'g', 'a', 'e', 'y', 'r'],
    lifeLeft: 5,
    secretWordLength: 7,
    knownSecretWord: 'bigbear',
  },
]

test('bigbear', 'boigaeyr', expected1)

// Test Case 2
const expected2: IGameState[] = [
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: [],
    lifeLeft: 7,
    secretWordLength: 7,
    knownSecretWord: '_______',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b'],
    lifeLeft: 7,
    secretWordLength: 7,
    knownSecretWord: 'b__b___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'b__b___',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'b__b_a_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e'],
    lifeLeft: 6,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e', 'n'],
    lifeLeft: 5,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e', 'n', 'u'],
    lifeLeft: 4,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e', 'n', 'u', 't'],
    lifeLeft: 3,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e', 'n', 'u', 't', 'z'],
    lifeLeft: 2,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.IN_PROGRESS,
    selectedLetters: ['b', 'o', 'a', 'e', 'n', 'u', 't', 'z', 'x'],
    lifeLeft: 1,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
  {
    status: GameStatus.LOSE,
    selectedLetters: ['b', 'o', 'a', 'e', 'n', 'u', 't', 'z', 'x', 'v'],
    lifeLeft: 0,
    secretWordLength: 7,
    knownSecretWord: 'b__bea_',
  },
]

test('bigbear', 'boaenutzxv', expected2)