~ubuntu-branches/ubuntu/vivid/phabricator/vivid-proposed

<?php

/**

 * Compute edit distance between two scalar sequences. This class uses

 * Levenshtein (or Damerau-Levenshtein) to compute the edit distance between

 * two inputs. The inputs are arrays containing any scalars (not just strings)

 * so it can be used with, e.g., utf8 sequences.

 *

 *  $matrix = id(new PhutilEditDistanceMatrix())

 *    ->setSequences(str_split('ran'), str_split('rat'));

 *

 *  $cost = $matrix->getEditDistance();

 *

 * Edit distance computation is slow and requires a large amount of memory;

 * both are roughly O(N * M) in the length of the strings.

 *

 * You can customize the cost of insertions, deletions and replacements. By

 * default, each has a cost of 1.

 *

 *   $matrix->setReplaceCost(1);

 *

 * By default, transpositions are not evaluated (i.e., the algorithm is

 * Levenshtein). You can cause transpositions to be evaluated by setting a

 * transpose cost (which will change the algorithm to Damerau-Levenshtein):

 *

 *   $matrix->setTransposeCost(1);

 *

 * You can also provide a cost to alter the type of operation being applied.

 * Many strings have several equivalently expensive edit sequences, but one

 * some sequences are more readable to humans than others. Providing a small

 * cost to alter operation type tends to smooth out the sequence and produce

 * long runs of a single operation, which are generally more readable. For

 * example, these strings:

 *

 *   (x)

 *   ((x))

 *

 * ...have edit strings "issis" and "isssi", which describe edit operations with

 * the same cost, but the latter string is more comprehensible to human viewers.

 *

 * If you set an alter cost, you must call @{method:setComputeString} to enable

 * type computation. The alter cost should generally be smaller than `c / N`,

 * where `c` is the smallest operational cost and `N` is the length of the

 * longest string. For example, if you are using the default costs (insert = 1,

 * delete = 1, replace = 1) and computing edit distances for strings of fewer

 * than 1,000 characters, you might set the alter cost to 0.001.

 */

final class PhutilEditDistanceMatrix {

  private $insertCost    = 1;

  private $deleteCost    = 1;

  private $replaceCost   = 1;

  private $transposeCost = null;

  private $alterCost     = 0;

  private $maximumLength;

  private $computeString;

  private $x;

  private $y;

  private $prefix;

  private $suffix;

  private $distanceMatrix = null;

  private $typeMatrix = null;

  public function setMaximumLength($maximum_length) {

    $this->maximumLength = $maximum_length;

    return $this;

  }

  public function getMaximumLength() {

    return coalesce($this->maximumLength, $this->getInfinity());

  }

  public function setComputeString($compute_string) {

    $this->computeString = $compute_string;

    return $this;

  }

  public function getComputeString() {

    return $this->computeString;

  }

  public function setTransposeCost($transpose_cost) {

    $this->transposeCost = $transpose_cost;

    return $this;

  }

  public function getTransposeCost() {

    return $this->transposeCost;

  }

  public function setReplaceCost($replace_cost) {

    $this->replaceCost = $replace_cost;

    return $this;

  }

  public function getReplaceCost() {

    return $this->replaceCost;

  }

  public function setDeleteCost($delete_cost) {

    $this->deleteCost = $delete_cost;

    return $this;

  }

  public function getDeleteCost() {

    return $this->deleteCost;

  }

  public function setInsertCost($insert_cost) {

    $this->insertCost = $insert_cost;

    return $this;

  }

  public function getInsertCost() {

    return $this->insertCost;

  }

  public function setAlterCost($alter_cost) {

    $this->alterCost = $alter_cost;

    return $this;

  }

  public function getAlterCost() {

    return $this->alterCost;

  }

  public function setSequences(array $x, array $y) {

    // NOTE: We strip common prefixes and suffixes from the inputs because

    // the runtime of the edit distance algorithm is large and it is common

    // to diff similar strings.

    $xl = count($x);

    $yl = count($y);

    $l = min($xl, $yl);

    $prefix_l = 0;

    $suffix_l = 0;

    for ($ii = 0; $ii < $l; $ii++) {

      if ($x[$ii] !== $y[$ii]) {

        break;

      }

      $prefix_l++;

    }

    for ($ii = 1; $ii <= ($l - $prefix_l); $ii++) {

      if ($x[$xl - $ii] !== $y[$yl - $ii]) {

        break;

      }

      $suffix_l++;

    }

    $this->prefix = array_slice($x, 0, $prefix_l);

    $this->suffix = array_slice($x, $xl - $suffix_l);

    $this->x = array_slice($x, $prefix_l, $xl - ($suffix_l + $prefix_l));

    $this->y = array_slice($y, $prefix_l, $yl - ($suffix_l + $prefix_l));

    $this->distanceMatrix = null;

    return $this;

  }

  private function requireSequences() {

    if ($this->x === null) {

      throw new Exception(

        'Call setSequences() before performing useful work!');

    }

  }

  public function getEditDistance() {

    $this->requireSequences();

    $x = $this->x;

    $y = $this->y;

    if (!$x) {

      return $this->insertCost * count($y);

    }

    if (!$y) {

      return $this->deleteCost * count($x);

    }

    $max = $this->getMaximumLength();

    if (count($x) > $max || count($y) > $max) {

      return ($this->insertCost * count($y)) + ($this->deleteCost * count($x));

    }

    if ($x === $y) {

      return 0;

    }

    $matrix = $this->getDistanceMatrix();

    return $matrix[count($x)][count($y)];

  }

  /**

   * Return a string representing the edits between the sequences. The string

   * has these characters:

   *

   *   - s (same): Same character in both strings.

   *   - i (insert): Character inserted.

   *   - d (delete): Character deleted.

   *   - x (replace): Character replaced.

   *   - t (transpose): Character transposed.

   */

  public function getEditString() {

    $this->requireSequences();

    $x = $this->x;

    $y = $this->y;

    if (!$x && !$y) {

      return $this->padEditString('');

    }

    if (!$x) {

      return $this->padEditString(str_repeat('i', count($y)));

    }

    if (!$y) {

      return $this->padEditString(str_repeat('d', count($x)));

    }

    if ($x === $y) {

      return $this->padEditString(str_repeat('s', count($x)));

    }

    $max = $this->getMaximumLength();

    if (count($x) > $max || count($y) > $max) {

      return $this->padEditString(

        str_repeat('d', count($x)).

        str_repeat('i', count($y)));

    }

    $matrix = $this->getTypeMatrix();

    $xx = count($x);

    $yy = count($y);

    $transposes = array();

    $str = '';

    while (true) {

      $type = $matrix[$xx][$yy];

      if (is_array($type)) {

        $chr = 't';

        $transposes[$type[0]][$type[1]] = true;

        $type = $type[2];

      } else {

        $chr = $type;

      }

      if (isset($transposes[$xx][$yy])) {

        $chr = 't';

      }

      if ($type == 's' || $type == 'x') {

        $xx -= 1;

        $yy -= 1;

      } else if ($type == 'i') {

        $yy -= 1;

      } else if ($type == 'd') {

        $xx -= 1;

      } else {

        throw new Exception("Unknown type '{$type}' in type matrix.");

      }

      $str .= $chr;

      if ($xx <= 0 && $yy <= 0) {

        break;

      }

    }

    return $this->padEditString(strrev($str));

  }

  private function padEditString($str) {

    if ($this->prefix) {

      $str = str_repeat('s', count($this->prefix)).$str;

    }

    if ($this->suffix) {

      $str = $str.str_repeat('s', count($this->suffix));

    }

    return $str;

  }

  private function getTypeMatrix() {

    if (!$this->computeString) {

      throw new Exception(

        'Call setComputeString() before getTypeMatrix().');

    }

    if ($this->typeMatrix === null) {

      $this->computeMatrix($this->x, $this->y);

    }

    return $this->typeMatrix;

  }

  private function getDistanceMatrix() {

    if ($this->distanceMatrix === null) {

      $this->computeMatrix($this->x, $this->y);

    }

    return $this->distanceMatrix;

  }

  private function computeMatrix(array $x, array $y) {

    $xl = count($x);

    $yl = count($y);

    $m = array();

    $infinity = $this->getInfinity();

    $use_damerau = ($this->transposeCost !== null);

    if ($use_damerau) {

      // Initialize the default cost of a transpose.

      $m[-1][-1] = $infinity;

      // Initialize the character position dictionary for Damerau.

      $d = array();

      foreach ($x as $c) {

        $d[$c] = -1;

      }

      foreach ($y as $c) {

        $d[$c] = -1;

      }

      // Initialize the transpose costs for Damerau.

      for ($xx = 0; $xx <= $xl; $xx++) {

        $m[$xx][-1] = $infinity;

      }

      for ($yy = 0; $yy <= $yl; $yy++) {

        $m[-1][$yy] = $infinity;

      }

    }

    // Initialize the top row of the matrix.

    for ($xx = 0; $xx <= $xl; $xx++) {

      $m[$xx][0] = $xx * $this->deleteCost;

    }

    // Initialize the left column of the matrix.

    $cost = 0;

    for ($yy = 0; $yy <= $yl; $yy++) {

      $m[0][$yy] = $yy * $this->insertCost;

    }

    $use_types = ($this->computeString);

    if ($use_types) {

      $t = array();

      for ($xx = 0; $xx <= $xl; $xx++) {

        $t[$xx][0] = 'd';

      }

      for ($yy = 0; $yy <= $yl; $yy++) {

        $t[0][$yy] = 'i';

      }

      $t[0][0] = 's';

    }

    $alt_cost = $this->getAlterCost();

    if ($alt_cost && !$use_types) {

      throw new Exception(

        'If you provide an alter cost with setAlterCost(), you must enable '.

        'type computation with setComputeStrings().');

    }

    // Build the edit distance matrix.

    for ($xx = 1; $xx <= $xl; $xx++) {

      $last_dy = -1;

      for ($yy = 1; $yy <= $yl; $yy++) {

        if ($use_damerau) {

          $dx = $d[$y[$yy - 1]];

          $dy = $last_dy;

        }

        if ($x[$xx - 1] === $y[$yy - 1]) {

          $rep_cost = $m[$xx - 1][$yy - 1] + 0;

          $rep_type = 's';

        } else {

          $rep_cost = $m[$xx - 1][$yy - 1] + $this->replaceCost;

          $rep_type = 'x';

        }

        $del_cost = $m[$xx - 1][$yy    ] + $this->deleteCost;

        $ins_cost = $m[$xx    ][$yy - 1] + $this->insertCost;

        if ($alt_cost) {

          $del_char = $t[$xx - 1][$yy    ];

          $ins_char = $t[$xx    ][$yy - 1];

          $rep_char = $t[$xx - 1][$yy - 1];

          if ($del_char !== 'd') {

            $del_cost += $alt_cost;

          }

          if ($ins_char !== 'i') {

            $ins_cost += $alt_cost;

          }

          if ($rep_char !== $rep_type) {

            $rep_cost += $alt_cost;

          }

        }

        if ($rep_cost <= $del_cost && $rep_cost <= $ins_cost) {

          $cost = $rep_cost;

          $type = $rep_type;

          if ($rep_type === 's') {

            $last_dy = $yy - 1;

          }

        } else if ($ins_cost <= $del_cost) {

          $cost = $ins_cost;

          $type = 'i';

        } else {

          $cost = $del_cost;

          $type = 'd';

        }

        if ($use_damerau) {

          $trn_count = (($xx - $dx - 2) + ($yy - $dy - 2) + 1);

          $trn_cost = $m[$dx][$dy] + ($trn_count * $this->transposeCost);

          if ($trn_cost < $cost) {

            $cost = $trn_cost;

            $type = array($dx + 1, $dy + 1, $type);

          }

        }

        $m[$xx][$yy] = $cost;

        if ($use_types) {

          $t[$xx][$yy] = $type;

        }

      }

      if ($use_damerau) {

        $d[$x[$xx - 1]] = ($xx - 1);

      }

    }

    $this->distanceMatrix = $m;

    if ($use_types) {

      $this->typeMatrix = $t;

    }

  }

  private function getInfinity() {

    return INF;

  }

  private function printMatrix(array $m) {

    $x = $this->x;

    $y = $this->y;

    $p = '% 8s ';

    printf($p, ' ');

    foreach (head($m) as $yk => $yv) {

      printf($p, idx($y, $yk - 1, '-'));

    }

    echo "\n";

    foreach ($m as $xk => $xv) {

      printf($p, idx($x, $xk - 1, '-'));

      foreach ($xv as $yk => $yv) {

        printf($p, ($yv == $this->getInfinity() ? 'inf' : $yv));

      }

      echo "\n";

    }

  }

  private function printTypeMatrix(array $t) {

    $x = $this->x;

    $y = $this->y;

    $p = '% 8s ';

    printf($p, ' ');

    foreach (head($t) as $yk => $yv) {

      printf($p, idx($y, $yk - 1, '-'));

    }

    echo "\n";

    foreach ($t as $xk => $xv) {

      printf($p, idx($x, $xk - 1, '-'));

      foreach ($xv as $yk => $yv) {

        printf($p, ($yv == $this->getInfinity() ? 'inf' : $yv));

      }

      echo "\n";

    }

  }

}