Generate pseudo-random phrases from Markov chains

markov.php

#!/usr/bin/env php
<?php
if (empty($argv[1]) || $argv[1] == '-h') {
  exit ("Usage: markov <input file> [words] [prefix] [minWords]\n");
}

$text = file_get_contents($argv[1]);
$map = map($text);
$words = $argv[2] ?? 20;
$minWords = $argv[4] ?? 10;
$prefix = $argv[3] ??  arand(prefixes($text));
echo markov($map, $prefix, $words, $minWords), "\n";

/**
 * Generate sentence from Markov map
 * @param  array  $map      Map of words
 * @param  string $prefix   Word to start with
 * @param  int    $maxWords Minimum number of words in result
 * @param  int    $minWords Maximum number of words in result
 * @return string
 */
function markov(
	array $map, string $prefix, int $maxWords = 20, int $minWords = 10
): string {
	$word = $prefix;
	$result = [$prefix];
	if (!array_key_exists($word, $map)) {
		throw new Exception("Prefix word does not exist in map!");
	}
	while (array_key_exists($word, $map) && count($result) <= $maxWords) {
		$word = arand($map[$word]);
		$result[] = $word;
		if (in_array($word{strlen($word) - 1}, ['.', '?', '!'])
			&& count($result) > $minWords
		) {
			break;
		}
	}
	return implode(' ', $result);
}

/**
 * Generate Markov pair map
 * @param  string $text  Text containing one or more phrases
 * @param  string $split Regular expression to split phrases on
 * @return array
 */
function map(string $text, string $split = "/\n/"): array {
	$map = [];
	if ($split === null) {
		$phrases = [$text];
	} else {
		$phrases = preg_split($split, $text);
	}
	foreach ($phrases as $phrase) {
		$words = preg_split("/[\s]+/", $phrase);
		$count = count($words);
		foreach ($words as $i=>$word) {
			if (!$word || $i >= $count - 1) {
				continue;
			}
			if (!array_key_exists($word, $map)) {
				$map[$word] = [];
			}
			$map[$word][] = $words[$i + 1];
		}
	}
	return $map;
}

/**
 * Generate array of prefix words
 * @param  string $text  Text containing one or more phrases
 * @param  string $split Regular expression to split phrases on
 * @return array
 */
function prefixes(string $text, string $split = "/\n/"): array {
	$phrases = preg_split($split, $text);
	$prefixes = [];
	foreach ($phrases as $phrase) {
		$word = explode(" ", $phrase, 2)[0];
		if (trim($word)) {
			$prefixes[] = trim($word);
		}
	}
	return $prefixes;
}

/**
 * Get random value from array using mt_rand
 * @param  array  $array
 * @return string
 */
function arand(array $array): string {
	$key = mt_rand(0, count($array) - 1);
	return $array[$key];
}