<?php

namespace alveolata\random;


/**
 * @return float in interval [0,1[
 */
function generate_unit(
) : float
{
	$max = \getrandmax();
	return (rand(0, $max) / $max);
}


/**
 * generate an integer value
 * 
 * @param float $probability the probability with which the result is "true"
 * @return bool
 */
function generate_boolean(
	$probability = 0.5
) : bool
{
	return (generate_unit() < $probability);
}


/**
 * generate an integer value
 * 
 * @param int $min the lowest possible generated value
 * @param int $max the highest possible generated value
 * @return int
 */
function generate_integer(
	int $min,
	int $max
) : int
{
	$t = generate_unit();
	return \intval(\floor($min + ($t * ($max - $min + 1))));
}


/**
 * generate a string value
 * 
 * @return string
 */
function generate_string(
	int $length = 16
) : string
{
	$string = '';
	for ($index = 0; $index < $length; $index += 1) {
		$string .= sprintf("%X", generate_integer(0, 15));
	}
	return $string;
}


/**
 * choose an element from a list with equal probabilities for all elements
 * 
 * @template type_element
 * @param array $list {list<§type_element>}
 * @return type_element
 */
function choose_uniformly(
	array $list
)
{
	$index = generate_integer(0, count($list)-1);
	return $list[$index];
}


/**
 * chooses a value randomly from a list of values with weights (a higher weight means a higher probability to be chosen)
 * 
 * @template type_element
 * @param array $list {list<record<element:§type_element,weight:float>>}
 * @return type_element
 */
function choose_weighted(
	array $sets
)
{
	$sum = array_reduce(
		$sets,
		function (float $sum, array $entry) : float {return ($sum + $entry['weight']);},
		0
	);
	if ($sum === 0) {
		throw (new \Exception('weights sum up to zero; are all zero or are negative weights included?'));
	}
	else {
		$position = generate_unit();
		return array_reduce(
			$sets,
			function ($current, $set) use ($sum, $position) {
				$next = ['index' => null, 'value' => null];
				$next['index'] = ($current['index'] + ($set['weight'] / $sum));
				$next['value'] = (
					(($current['index'] <= $position) && ($position < $next['index']))
					? $set['value']
					: $current['value']
				);
				return $next;
			},
			['index' => 0, 'value' => null]
		)['value'];
	}
}


/**
 * @return string
 */
function generate_vowel(
) : string
{
	return choose_weighted([
		['value' => 'i', 'weight' => 1],
		['value' => 'e', 'weight' => 2],
		['value' => 'a', 'weight' => 3],
		['value' => 'o', 'weight' => 2],
		['value' => 'u', 'weight' => 1],
	]);
}


/**
 * @return string
 */
function generate_semivowel(
) : string
{
	return choose_weighted([
		['value' => 'y', 'weight' => 2],
		['value' => 'w', 'weight' => 1],
	]);
}


/**
 * @return string
 */
function generate_lateral_approximant(
) : string
{
	return choose_weighted([
		['value' => 'l', 'weight' => 1],
	]);
}


/**
 * @return string
 */
function generate_nasal(
) : string
{
	return choose_weighted([
		['value' => 'n', 'weight' => 4],
		['value' => 'm', 'weight' => 2],
		['value' => 'q', 'weight' => 1],
	]);
}


/**
 * @return string
 */
function generate_plosive(
) : string
{
	return choose_weighted([
		['value' => 'b', 'weight' => 1],
		['value' => 'p', 'weight' => 2],
		['value' => 'd', 'weight' => 1],
		['value' => 't', 'weight' => 2],
		['value' => 'g', 'weight' => 1],
		['value' => 'k', 'weight' => 2],
	]);
}


/**
 * @return string
 */
function generate_fricative(
) : string
{
	return choose_weighted([
		['value' => 'r', 'weight' => 2],
		['value' => 'h', 'weight' => 1],
		['value' => 'x', 'weight' => 1],
		['value' => 'j', 'weight' => 1],
		['value' => 'c', 'weight' => 1],
		['value' => 'v', 'weight' => 2],
		['value' => 'f', 'weight' => 2],
		['value' => 's', 'weight' => 2],
		['value' => 'z', 'weight' => 2],
	]);
}


/**
 * @return string
 */
function generate_consonant(
) : string
{
	return choose_weighted([
		['value' => generate_lateral_approximant(), 'weight' => 1],
		['value' => generate_nasal(), 'weight' => 1],
		['value' => generate_plosive(), 'weight' => 1],
		['value' => generate_fricative(), 'weight' => 1],
	]);
}


/**
 * @return string
 */
function generate_syllable(
) : string
{
	/*
	+---+---+---+---+---+---+---+
	|   | L | N | P | F | S | V |
	+---+---+---+---+---+---+---+
	| L |   | o | x | x | o | x |
	+---+---+---+---+---+---+---+
	| N |   |   | o | x |   | x |
	+---+---+---+---+---+---+---+
	| P | x | o | o | x | x | x |
	+---+---+---+---+---+---+---+
	| F | x | o |   | o | x | x |
	+---+---+---+---+---+---+---+
	| S | x | x | x | x |   | x |
	+---+---+---+---+---+---+---+
	| V | x | x | x | x | x | o |
	+---+---+---+---+---+---+---+
	
	{L,N,P,F}
	{LP,LF,NF,NP,PL,PF,FL}
	{LPF,NPL,NPF,PFL}
	
	pflantze
	glas
	crayb-tic
	
	
	 */
	$length1 = choose_weighted([
		['value' => 1, 'weight' => 3],
		['value' => 2, 'weight' => 4],
		['value' => 3, 'weight' => 1],
	]);
	
	return sprintf(
		'%s%s%s',
		generate_consonant(),
		generate_vowel(),
		(generate_boolean(0.125) ? generate_semivowel() : '')
	);
}


/**
 * @return string
 */
function generate_word(
) : string
{
	$length = generate_integer(1, 4);
	$syllables = [];
	for ($index = 0; $index < $length; $index += 1) {
		$syllables[] = generate_syllable();
	}
	return implode('', $syllables);
}


/**
 * @return string
 */
function generate_text(
) : string
{
	$length = generate_integer(8, 32);
	$words = [];
	for ($index = 0; $index < $length; $index += 1) {
		$words[] = generate_word();
	}
	return implode(' ', $words);
}

 ?>