Takes a file with a list of sentences that are separated by newlines where words are space delimited. This assumes the file only has characters ` A-z0-9 ` and ` <>~#$%^&()-_=+/ ` and ` ' " `

markov_maker.js

const fs = require('fs');

const all_lines = fs.readFileSync('./forums_but_nice.txt', 'utf8')
    .slice(0, -1)
    .split('\n')
    .map(e => e.split(' ').map(p => p.toLowerCase()));
const all_words = {};
all_lines.forEach(line => line.forEach(word => 
    all_words[word] ? all_words[word]++ : all_words[word] = 1
));

function random_word(){
    const total = Object.values(all_words).reduce((a,b) => a + b);
    const target = Math.floor(Math.random() * total) + 1;
    let counter = 0;
    return Object.entries(all_words).find(([word, count]) => target <= (counter += count))[0];
}

function hasSubArray(master, sub){
    const start = master.indexOf(sub[0])
    return sub.every((word, i) => master[start + i] == word);
}

function find_next(...words){
    const last_word = words[words.length - 1];
    const possible_words = all_lines
        .filter(l => hasSubArray(l, words))
        .map(l => l[l.indexOf(last_word) + 1]);
    const random_index = Math.floor(Math.random() * possible_words.length) + 1;
    const next_word = possible_words[random_index];
    return next_word;
}

function recurse(max = 20, ...words){
    if(max == 0){ return words.join(' '); }
    let next_word = find_next(...words);
    let counter = 0;
    while(next_word == undefined && counter != words.length && (counter!=words.length-1?true:Math.random()>0.9)){
        counter++;
        next_word = find_next(...words.slice(counter))
    }
    if(next_word == undefined){ return words.join(' '); }
    return words[0] + ' ' + recurse(max-1, ...words.concat(next_word).slice(1));
}

function sentence(start){
    const numwords = Math.floor(Math.random() * 15 + Math.random() * 8 + 7)
    const a = [random_word()];
    for(let i = 1; i < start; i++){
        const next = find_next(...a);
        if(next == undefined){ break; }
        a.push(next);
    }
    const words = recurse(numwords, ...a);
    return words.charAt(0).toUpperCase() + words.slice(1) + '.';
}

function text(){
    const len = Math.floor(Math.random() * 2) + Math.floor(Math.random() * 2) + 1;
    return sentence(len);
}