hangman.ts

import {from, Observable} from 'rxjs';
import {reduce} from "rxjs/operators";
import reduceReducers from "reduce-reducers";

const MAX_LIFE = 7;

const zip = (arr1: Array<string>, arr2: Array<string>) => arr1.map((e, i) => [e, arr2[i]])

type State = {
    status: string,
    knownSecretWord: Array<string>,
    selectedLetters: Set<string>,
    secretWordLength: number,
    lifeLeft: number
}

type HangmanReducer = (state: State, guessCh: string) => State

const createHangmanReducers: ((_: string) => HangmanReducer) = (secretWord: string) => {
    const word = secretWord.split('');
    ;

    const knownSecretWordReducer = (state: State, guessCh: string) => ({
        ...state, knownSecretWord: zip(word, state.knownSecretWord)
            .map(([ch, revealCh]) => ch === guessCh ? ch : revealCh)
    });

    const leftLeftReducer = (state: State, guessCh: string) => ({
        ...state,
        lifeLeft: word.some(w => w === guessCh) ? state.lifeLeft : state.lifeLeft - 1
    });

    const selectedLettersReducer = (state: State, guessCh: string) => ({
        ...state,
        selectedLetters: state.selectedLetters.add(guessCh)
    });

    const statusReducer = (state: State, guessCh: string) => ({
        ...state, status: state.lifeLeft <= 0 ? 'lose' :
            (state.knownSecretWord.some((ch: string) => ch === '_') ? 'in-progress' : 'win')
    });

    return reduceReducers(knownSecretWordReducer, leftLeftReducer, selectedLettersReducer, statusReducer);
};

function reactiveHangman(secretWord: string, letters: Observable<string>): Observable<object> {
    return reduce(createHangmanReducers(secretWord), {
        status: 'in-progress',
        knownSecretWord: secretWord.split('').map(_ => '_'),
        selectedLetters: new Set([]),
        secretWordLength: secretWord.length,
        lifeLeft: MAX_LIFE
    })(letters);
}