PhutilArgumentSpellingCorrector.php
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	<?php

	final class PhutilArgumentSpellingCorrector extends Phobject {

	private $editDistanceMatrix;
	private $maximumDistance;
	private $mode;

	const MODE_COMMANDS = 'commands';
	const MODE_FLAGS = 'flags';

	/**
	* Build a new corrector with parameters for correcting commands, like
	* fixing "dfif" into "diff" in "arc diff".
	*
	* @return PhutilArgumentSpellingCorrector Configured corrector.
	*/
	public static function newCommandCorrector() {
	// When correcting argument spelling, we're relatively liberal about
	// selecting alternatives and allow multiple mistakes.
	$max_distance = 2;

	// Adjust to the scaled edit costs we use below, so "2" roughly means
	// "2 edits".
	$max_distance = $max_distance * 3;

	// These costs are somewhat made up, but the theory is that it is far more
	// likely you will mis-strike a key ("lans" for "land") or press two keys
	// out of order ("alnd" for "land") than omit keys or press extra keys.
	$matrix = id(new PhutilEditDistanceMatrix())
	->setInsertCost(4)
	->setDeleteCost(4)
	->setReplaceCost(3)
	->setTransposeCost(2);

	return id(new self())
	->setEditDistanceMatrix($matrix)
	->setMode(self::MODE_COMMANDS)
	->setMaximumDistance($max_distance);
	}


	/**
	* Build a new corrector with parameters for correcting flags, like
	* fixing "--nolint" into "--no-lint".
	*
	* @return PhutilArgumentSpellingCorrector Configured corrector.
	*/
	public static function newFlagCorrector() {
	// When correcting flag spelling, we're stricter than we are when
	// correcting command spelling: we allow only one inserted or deleted
	// character. It is mainly to handle cases like "--no-lint" versus
	// "--nolint" or "--reviewer" versus "--reviewers".
	$max_distance = 1;

	$matrix = id(new PhutilEditDistanceMatrix())
	->setInsertCost(1)
	->setDeleteCost(1)
	->setReplaceCost(10);

	return id(new self())
	->setEditDistanceMatrix($matrix)
	->setMode(self::MODE_FLAGS)
	->setMaximumDistance($max_distance);
	}

	public function setMode($mode) {
	$this->mode = $mode;
	return $this;
	}

	public function getMode() {
	return $this->mode;
	}

	public function setEditDistanceMatrix(PhutilEditDistanceMatrix $matrix) {
	$this->editDistanceMatrix = $matrix;
	return $this;
	}

	public function getEditDistanceMatrix() {
	return $this->editDistanceMatrix;
	}

	public function setMaximumDistance($maximum_distance) {
	$this->maximumDistance = $maximum_distance;
	return $this;
	}

	public function getMaximumDistance() {
	return $this->maximumDistance;
	}

	public function correctSpelling($input, array $options) {
	$matrix = $this->getEditDistanceMatrix();
	if (!$matrix) {
	throw new PhutilInvalidStateException('setEditDistanceMatrix');
	}

	$max_distance = $this->getMaximumDistance();
	if (!$max_distance) {
	throw new PhutilInvalidStateException('setMaximumDistance');
	}

	// If we're correcting commands, never correct an input which begins
	// with "-", since this is almost certainly intended to be a flag.
	if ($this->getMode() === self::MODE_COMMANDS) {
	if (preg_match('/^-/', $input)) {
	return array();
	}
	}

	$input = $this->normalizeString($input);
	foreach ($options as $key => $option) {
	$options[$key] = $this->normalizeString($option);
	}

	// In command mode, accept any unique prefix of a command as a shorthand
	// for that command.
	if ($this->getMode() === self::MODE_COMMANDS) {
	$prefixes = array();
	foreach ($options as $option) {
	if (!strncmp($input, $option, strlen($input))) {
	$prefixes[] = $option;
	}
	}

	if (count($prefixes) === 1) {
	return $prefixes;
	}
	}

	$distances = array();
	$inputv = phutil_utf8v($input);
	foreach ($options as $option) {
	$optionv = phutil_utf8v($option);
	$matrix->setSequences($optionv, $inputv);
	$distances[$option] = $matrix->getEditDistance();
	}

	asort($distances);
	$best = min($max_distance, head($distances));
	foreach ($distances as $option => $distance) {
	if ($distance > $best) {
	unset($distances[$option]);
	}
	}

	// Before filtering, check if we have multiple equidistant matches and
	// return them if we do. This prevents us from, e.g., matching "alnd" with
	// both "land" and "amend", then dropping "land" for being too short, and
	// incorrectly completing to "amend".
	if (count($distances) > 1) {
	return array_keys($distances);
	}

	foreach ($distances as $option => $distance) {
	if (phutil_utf8_strlen($option) < $distance) {
	unset($distances[$option]);
	}
	}

	return array_keys($distances);
	}

	private function normalizeString($string) {
	return phutil_utf8_strtolower($string);
	}

	}

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