RomanNumerals.php
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	<?php
	declare(strict_types=1);

	namespace Keruald\OmniTools\Culture\Rome;

	use InvalidArgumentException;

	final class RomanNumerals {

	public static function fromHinduArabic (int $number) : string {
	self::assertStrictlyPositiveNumber($number);

	if ($number > 1000) {
	return self::computeFromKiloHinduArabic($number);
	}

	$table = self::getHinduArabicTable();

	return $table[$number] ?? self::computeFromHinduArabic($number);
	}

	/**
	* Provides a canonical table with hindu arabic numerals as keys,
	* and roman numerals as values.
	*/
	public static function getHinduArabicTable () : array {
	return [
	1 => 'i',
	2 => 'ii',
	3 => 'iii',
	4 => 'iv',
	5 => 'v',
	6 => 'vi',
	7 => 'vii',
	8 => 'viii',
	9 => 'ix',
	10 => 'x',
	50 => 'l',
	100 => 'c',
	500 => 'd',
	1000 => 'm',
	];
	}

	private static function getComputeHinduArabicTable () : iterable {
	// limit => number to subtract (as a [roman, hindu arabic] array)
	yield 21 => ['x', 10];
	yield 30 => ['xx', 20];
	yield 40 => ['xxx', 30];
	yield 50 => ['xl', 40];
	yield 60 => ['l', 50];
	yield 70 => ['lx', 60];
	yield 80 => ['lxx', 70];
	yield 90 => ['lxxx', 80];
	yield 100 => ['xc', 90];
	yield 200 => ['c', 100];
	yield 300 => ['cc', 200];
	yield 400 => ['ccc', 300];
	yield 500 => ['cd', 400];
	yield 600 => ['d', 500];
	yield 700 => ['dc', 600];
	yield 800 => ['dcc', 700];
	yield 900 => ['dccc', 800];
	yield 1000 => ['cm', 900];
	}

	private static function computeFromHinduArabic (int $number) : string {
	foreach (self::getComputeHinduArabicTable() as $limit => $term) {
	if ($number < $limit) {
	return $term[0] . self::fromHinduArabic($number - $term[1]);
	}
	}

	throw new \LogicException("This should be unreachable code.");
	}

	private static function computeFromKiloHinduArabic (int $number) : string {
	$thousandAmount = (int)floor($number / 1000);
	$remainder = $number % 1000;

	$roman = str_repeat('m', $thousandAmount);
	if ($remainder > 0) {
	$roman .= self::fromHinduArabic($remainder);
	}

	return $roman;
	}

	private static function assertStrictlyPositiveNumber (int $number) : void {
	if ($number < 1) {
	throw new InvalidArgumentException(
	"Can only convert strictly positive numbers"
	);
	}
	}
	}

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