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Differences Between: [Versions 39 and 310] [Versions 39 and 311] [Versions 39 and 400] [Versions 39 and 401] [Versions 39 and 402] [Versions 39 and 403]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  
  18  /**
  19   * Question type class for the numerical question type.
  20   *
  21   * @package    qtype
  22   * @subpackage numerical
  23   * @copyright  1999 onwards Martin Dougiamas {@link http://moodle.com}
  24   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  25   */
  26  
  27  
  28  defined('MOODLE_INTERNAL') || die();
  29  
  30  require_once($CFG->libdir . '/questionlib.php');
  31  require_once($CFG->dirroot . '/question/type/numerical/question.php');
  32  
  33  
  34  /**
  35   * The numerical question type class.
  36   *
  37   * This class contains some special features in order to make the
  38   * question type embeddable within a multianswer (cloze) question
  39   *
  40   * @copyright  1999 onwards Martin Dougiamas {@link http://moodle.com}
  41   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  42   */
  43  class qtype_numerical extends question_type {
  44      const UNITINPUT = 0;
  45      const UNITRADIO = 1;
  46      const UNITSELECT = 2;
  47  
  48      const UNITNONE = 3;
  49      const UNITGRADED = 1;
  50      const UNITOPTIONAL = 0;
  51  
  52      const UNITGRADEDOUTOFMARK = 1;
  53      const UNITGRADEDOUTOFMAX = 2;
  54  
  55      /**
  56       * Validate that a string is a number formatted correctly for the current locale.
  57       * @param string $x a string
  58       * @return bool whether $x is a number that the numerical question type can interpret.
  59       */
  60      public static function is_valid_number(string $x) : bool {
  61          $ap = new qtype_numerical_answer_processor(array());
  62          list($value, $unit) = $ap->apply_units($x);
  63          return !is_null($value) && !$unit;
  64      }
  65  
  66      public function get_question_options($question) {
  67          global $CFG, $DB, $OUTPUT;
  68          parent::get_question_options($question);
  69          // Get the question answers and their respective tolerances
  70          // Note: question_numerical is an extension of the answer table rather than
  71          //       the question table as is usually the case for qtype
  72          //       specific tables.
  73          if (!$question->options->answers = $DB->get_records_sql(
  74                                  "SELECT a.*, n.tolerance " .
  75                                  "FROM {question_answers} a, " .
  76                                  "     {question_numerical} n " .
  77                                  "WHERE a.question = ? " .
  78                                  "    AND   a.id = n.answer " .
  79                                  "ORDER BY a.id ASC", array($question->id))) {
  80              echo $OUTPUT->notification('Error: Missing question answer for numerical question ' .
  81                      $question->id . '!');
  82              return false;
  83          }
  84  
  85          $question->hints = $DB->get_records('question_hints',
  86                  array('questionid' => $question->id), 'id ASC');
  87  
  88          $this->get_numerical_units($question);
  89          // Get_numerical_options() need to know if there are units
  90          // to set correctly default values.
  91          $this->get_numerical_options($question);
  92  
  93          // If units are defined we strip off the default unit from the answer, if
  94          // it is present. (Required for compatibility with the old code and DB).
  95          if ($defaultunit = $this->get_default_numerical_unit($question)) {
  96              foreach ($question->options->answers as $key => $val) {
  97                  $answer = trim($val->answer);
  98                  $length = strlen($defaultunit->unit);
  99                  if ($length && substr($answer, -$length) == $defaultunit->unit) {
 100                      $question->options->answers[$key]->answer =
 101                              substr($answer, 0, strlen($answer)-$length);
 102                  }
 103              }
 104          }
 105  
 106          return true;
 107      }
 108  
 109      public function get_numerical_units(&$question) {
 110          global $DB;
 111  
 112          if ($units = $DB->get_records('question_numerical_units',
 113                  array('question' => $question->id), 'id ASC')) {
 114              $units = array_values($units);
 115          } else {
 116              $units = array();
 117          }
 118          foreach ($units as $key => $unit) {
 119              $units[$key]->multiplier = clean_param($unit->multiplier, PARAM_FLOAT);
 120          }
 121          $question->options->units = $units;
 122          return true;
 123      }
 124  
 125      public function get_default_numerical_unit($question) {
 126          if (isset($question->options->units[0])) {
 127              foreach ($question->options->units as $unit) {
 128                  if (abs($unit->multiplier - 1.0) < '1.0e-' . ini_get('precision')) {
 129                      return $unit;
 130                  }
 131              }
 132          }
 133          return false;
 134      }
 135  
 136      public function get_numerical_options($question) {
 137          global $DB;
 138          if (!$options = $DB->get_record('question_numerical_options',
 139                  array('question' => $question->id))) {
 140              // Old question, set defaults.
 141              $question->options->unitgradingtype = 0;
 142              $question->options->unitpenalty = 0.1;
 143              if ($defaultunit = $this->get_default_numerical_unit($question)) {
 144                  $question->options->showunits = self::UNITINPUT;
 145              } else {
 146                  $question->options->showunits = self::UNITNONE;
 147              }
 148              $question->options->unitsleft = 0;
 149  
 150          } else {
 151              $question->options->unitgradingtype = $options->unitgradingtype;
 152              $question->options->unitpenalty = $options->unitpenalty;
 153              $question->options->showunits = $options->showunits;
 154              $question->options->unitsleft = $options->unitsleft;
 155          }
 156  
 157          return true;
 158      }
 159  
 160      /**
 161       * Save the units and the answers associated with this question.
 162       */
 163      public function save_question_options($question) {
 164          global $DB;
 165          $context = $question->context;
 166  
 167          // Get old versions of the objects.
 168          $oldanswers = $DB->get_records('question_answers',
 169                  array('question' => $question->id), 'id ASC');
 170          $oldoptions = $DB->get_records('question_numerical',
 171                  array('question' => $question->id), 'answer ASC');
 172  
 173          // Save the units.
 174          $result = $this->save_units($question);
 175          if (isset($result->error)) {
 176              return $result;
 177          } else {
 178              $units = $result->units;
 179          }
 180  
 181          // Insert all the new answers.
 182          foreach ($question->answer as $key => $answerdata) {
 183              // Check for, and ingore, completely blank answer from the form.
 184              if (trim($answerdata) == '' && $question->fraction[$key] == 0 &&
 185                      html_is_blank($question->feedback[$key]['text'])) {
 186                  continue;
 187              }
 188  
 189              // Update an existing answer if possible.
 190              $answer = array_shift($oldanswers);
 191              if (!$answer) {
 192                  $answer = new stdClass();
 193                  $answer->question = $question->id;
 194                  $answer->answer = '';
 195                  $answer->feedback = '';
 196                  $answer->id = $DB->insert_record('question_answers', $answer);
 197              }
 198  
 199              if (trim($answerdata) === '*') {
 200                  $answer->answer = '*';
 201              } else {
 202                  $answer->answer = $this->apply_unit($answerdata, $units,
 203                          !empty($question->unitsleft));
 204                  if ($answer->answer === false) {
 205                      $result->notice = get_string('invalidnumericanswer', 'qtype_numerical');
 206                  }
 207              }
 208              $answer->fraction = $question->fraction[$key];
 209              $answer->feedback = $this->import_or_save_files($question->feedback[$key],
 210                      $context, 'question', 'answerfeedback', $answer->id);
 211              $answer->feedbackformat = $question->feedback[$key]['format'];
 212              $DB->update_record('question_answers', $answer);
 213  
 214              // Set up the options object.
 215              if (!$options = array_shift($oldoptions)) {
 216                  $options = new stdClass();
 217              }
 218              $options->question = $question->id;
 219              $options->answer   = $answer->id;
 220              if (trim($question->tolerance[$key]) == '') {
 221                  $options->tolerance = '';
 222              } else {
 223                  $options->tolerance = $this->apply_unit($question->tolerance[$key],
 224                          $units, !empty($question->unitsleft));
 225                  if ($options->tolerance === false) {
 226                      $result->notice = get_string('invalidnumerictolerance', 'qtype_numerical');
 227                  }
 228                  $options->tolerance = (string)$options->tolerance;
 229              }
 230              if (isset($options->id)) {
 231                  $DB->update_record('question_numerical', $options);
 232              } else {
 233                  $DB->insert_record('question_numerical', $options);
 234              }
 235          }
 236  
 237          // Delete any left over old answer records.
 238          $fs = get_file_storage();
 239          foreach ($oldanswers as $oldanswer) {
 240              $fs->delete_area_files($context->id, 'question', 'answerfeedback', $oldanswer->id);
 241              $DB->delete_records('question_answers', array('id' => $oldanswer->id));
 242          }
 243          foreach ($oldoptions as $oldoption) {
 244              $DB->delete_records('question_numerical', array('id' => $oldoption->id));
 245          }
 246  
 247          $result = $this->save_unit_options($question);
 248          if (!empty($result->error) || !empty($result->notice)) {
 249              return $result;
 250          }
 251  
 252          $this->save_hints($question);
 253  
 254          return true;
 255      }
 256  
 257      /**
 258       * The numerical options control the display and the grading of the unit
 259       * part of the numerical question and related types (calculateds)
 260       * Questions previous to 2.0 do not have this table as multianswer questions
 261       * in all versions including 2.0. The default values are set to give the same grade
 262       * as old question.
 263       *
 264       */
 265      public function save_unit_options($question) {
 266          global $DB;
 267          $result = new stdClass();
 268  
 269          $update = true;
 270          $options = $DB->get_record('question_numerical_options',
 271                  array('question' => $question->id));
 272          if (!$options) {
 273              $options = new stdClass();
 274              $options->question = $question->id;
 275              $options->id = $DB->insert_record('question_numerical_options', $options);
 276          }
 277  
 278          if (isset($question->unitpenalty)) {
 279              $options->unitpenalty = $question->unitpenalty;
 280          } else {
 281              // Either an old question or a close question type.
 282              $options->unitpenalty = 1;
 283          }
 284  
 285          $options->unitgradingtype = 0;
 286          if (isset($question->unitrole)) {
 287              // Saving the editing form.
 288              $options->showunits = $question->unitrole;
 289              if ($question->unitrole == self::UNITGRADED) {
 290                  $options->unitgradingtype = $question->unitgradingtypes;
 291                  $options->showunits = $question->multichoicedisplay;
 292              }
 293  
 294          } else if (isset($question->showunits)) {
 295              // Updated import, e.g. Moodle XML.
 296              $options->showunits = $question->showunits;
 297              if (isset($question->unitgradingtype)) {
 298                  $options->unitgradingtype = $question->unitgradingtype;
 299              }
 300          } else {
 301              // Legacy import.
 302              if ($defaultunit = $this->get_default_numerical_unit($question)) {
 303                  $options->showunits = self::UNITINPUT;
 304              } else {
 305                  $options->showunits = self::UNITNONE;
 306              }
 307          }
 308  
 309          $options->unitsleft = !empty($question->unitsleft);
 310  
 311          $DB->update_record('question_numerical_options', $options);
 312  
 313          // Report any problems.
 314          if (!empty($result->notice)) {
 315              return $result;
 316          }
 317  
 318          return true;
 319      }
 320  
 321      public function save_units($question) {
 322          global $DB;
 323          $result = new stdClass();
 324  
 325          // Delete the units previously saved for this question.
 326          $DB->delete_records('question_numerical_units', array('question' => $question->id));
 327  
 328          // Nothing to do.
 329          if (!isset($question->multiplier)) {
 330              $result->units = array();
 331              return $result;
 332          }
 333  
 334          // Save the new units.
 335          $units = array();
 336          $unitalreadyinsert = array();
 337          foreach ($question->multiplier as $i => $multiplier) {
 338              // Discard any unit which doesn't specify the unit or the multiplier.
 339              if (!empty($question->multiplier[$i]) && !empty($question->unit[$i]) &&
 340                      !array_key_exists($question->unit[$i], $unitalreadyinsert)) {
 341                  $unitalreadyinsert[$question->unit[$i]] = 1;
 342                  $units[$i] = new stdClass();
 343                  $units[$i]->question = $question->id;
 344                  $units[$i]->multiplier = $this->apply_unit($question->multiplier[$i],
 345                          array(), false);
 346                  $units[$i]->unit = $question->unit[$i];
 347                  $DB->insert_record('question_numerical_units', $units[$i]);
 348              }
 349          }
 350          unset($question->multiplier, $question->unit);
 351  
 352          $result->units = &$units;
 353          return $result;
 354      }
 355  
 356      protected function initialise_question_instance(question_definition $question, $questiondata) {
 357          parent::initialise_question_instance($question, $questiondata);
 358          $this->initialise_numerical_answers($question, $questiondata);
 359          $question->unitdisplay = $questiondata->options->showunits;
 360          $question->unitgradingtype = $questiondata->options->unitgradingtype;
 361          $question->unitpenalty = $questiondata->options->unitpenalty;
 362          $question->ap = $this->make_answer_processor($questiondata->options->units,
 363                  $questiondata->options->unitsleft);
 364      }
 365  
 366      public function initialise_numerical_answers(question_definition $question, $questiondata) {
 367          $question->answers = array();
 368          if (empty($questiondata->options->answers)) {
 369              return;
 370          }
 371          foreach ($questiondata->options->answers as $a) {
 372              $question->answers[$a->id] = new qtype_numerical_answer($a->id, $a->answer,
 373                      $a->fraction, $a->feedback, $a->feedbackformat, $a->tolerance);
 374          }
 375      }
 376  
 377      public function make_answer_processor($units, $unitsleft) {
 378          if (empty($units)) {
 379              return new qtype_numerical_answer_processor(array());
 380          }
 381  
 382          $cleanedunits = array();
 383          foreach ($units as $unit) {
 384              $cleanedunits[$unit->unit] = $unit->multiplier;
 385          }
 386  
 387          return new qtype_numerical_answer_processor($cleanedunits, $unitsleft);
 388      }
 389  
 390      public function delete_question($questionid, $contextid) {
 391          global $DB;
 392          $DB->delete_records('question_numerical', array('question' => $questionid));
 393          $DB->delete_records('question_numerical_options', array('question' => $questionid));
 394          $DB->delete_records('question_numerical_units', array('question' => $questionid));
 395  
 396          parent::delete_question($questionid, $contextid);
 397      }
 398  
 399      public function get_random_guess_score($questiondata) {
 400          foreach ($questiondata->options->answers as $aid => $answer) {
 401              if ('*' == trim($answer->answer)) {
 402                  return max($answer->fraction - $questiondata->options->unitpenalty, 0);
 403              }
 404          }
 405          return 0;
 406      }
 407  
 408      /**
 409       * Add a unit to a response for display.
 410       * @param object $questiondata the data defining the quetsion.
 411       * @param string $answer a response.
 412       * @param object $unit a unit. If null, {@link get_default_numerical_unit()}
 413       * is used.
 414       */
 415      public function add_unit($questiondata, $answer, $unit = null) {
 416          if (is_null($unit)) {
 417              $unit = $this->get_default_numerical_unit($questiondata);
 418          }
 419  
 420          if (!$unit) {
 421              return $answer;
 422          }
 423  
 424          if (!empty($questiondata->options->unitsleft)) {
 425              return $unit->unit . ' ' . $answer;
 426          } else {
 427              return $answer . ' ' . $unit->unit;
 428          }
 429      }
 430  
 431      public function get_possible_responses($questiondata) {
 432          $responses = array();
 433  
 434          $unit = $this->get_default_numerical_unit($questiondata);
 435  
 436          $starfound = false;
 437          foreach ($questiondata->options->answers as $aid => $answer) {
 438              $responseclass = $answer->answer;
 439  
 440              if ($responseclass === '*') {
 441                  $starfound = true;
 442              } else {
 443                  $responseclass = $this->add_unit($questiondata, $responseclass, $unit);
 444  
 445                  $ans = new qtype_numerical_answer($answer->id, $answer->answer, $answer->fraction,
 446                          $answer->feedback, $answer->feedbackformat, $answer->tolerance);
 447                  list($min, $max) = $ans->get_tolerance_interval();
 448                  $responseclass .= " ({$min}..{$max})";
 449              }
 450  
 451              $responses[$aid] = new question_possible_response($responseclass,
 452                      $answer->fraction);
 453          }
 454  
 455          if (!$starfound) {
 456              $responses[0] = new question_possible_response(
 457                      get_string('didnotmatchanyanswer', 'question'), 0);
 458          }
 459  
 460          $responses[null] = question_possible_response::no_response();
 461  
 462          return array($questiondata->id => $responses);
 463      }
 464  
 465      /**
 466       * Checks if the $rawresponse has a unit and applys it if appropriate.
 467       *
 468       * @param string $rawresponse  The response string to be converted to a float.
 469       * @param array $units         An array with the defined units, where the
 470       *                             unit is the key and the multiplier the value.
 471       * @return float               The rawresponse with the unit taken into
 472       *                             account as a float.
 473       */
 474      public function apply_unit($rawresponse, $units, $unitsleft) {
 475          $ap = $this->make_answer_processor($units, $unitsleft);
 476          list($value, $unit, $multiplier) = $ap->apply_units($rawresponse);
 477          if (!is_null($multiplier)) {
 478              $value *= $multiplier;
 479          }
 480          return $value;
 481      }
 482  
 483      public function move_files($questionid, $oldcontextid, $newcontextid) {
 484          $fs = get_file_storage();
 485  
 486          parent::move_files($questionid, $oldcontextid, $newcontextid);
 487          $this->move_files_in_answers($questionid, $oldcontextid, $newcontextid);
 488          $this->move_files_in_hints($questionid, $oldcontextid, $newcontextid);
 489      }
 490  
 491      protected function delete_files($questionid, $contextid) {
 492          $fs = get_file_storage();
 493  
 494          parent::delete_files($questionid, $contextid);
 495          $this->delete_files_in_answers($questionid, $contextid);
 496          $this->delete_files_in_hints($questionid, $contextid);
 497      }
 498  }
 499  
 500  
 501  /**
 502   * This class processes numbers with units.
 503   *
 504   * @copyright 2010 The Open University
 505   * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 506   */
 507  class qtype_numerical_answer_processor {
 508      /** @var array unit name => multiplier. */
 509      protected $units;
 510      /** @var string character used as decimal point. */
 511      protected $decsep;
 512      /** @var string character used as thousands separator. */
 513      protected $thousandssep;
 514      /** @var boolean whether the units come before or after the number. */
 515      protected $unitsbefore;
 516  
 517      protected $regex = null;
 518  
 519      public function __construct($units, $unitsbefore = false, $decsep = null,
 520              $thousandssep = null) {
 521          if (is_null($decsep)) {
 522              $decsep = get_string('decsep', 'langconfig');
 523          }
 524          $this->decsep = $decsep;
 525  
 526          if (is_null($thousandssep)) {
 527              $thousandssep = get_string('thousandssep', 'langconfig');
 528          }
 529          $this->thousandssep = $thousandssep;
 530  
 531          $this->units = $units;
 532          $this->unitsbefore = $unitsbefore;
 533      }
 534  
 535      /**
 536       * Set the decimal point and thousands separator character that should be used.
 537       * @param string $decsep
 538       * @param string $thousandssep
 539       */
 540      public function set_characters($decsep, $thousandssep) {
 541          $this->decsep = $decsep;
 542          $this->thousandssep = $thousandssep;
 543          $this->regex = null;
 544      }
 545  
 546      /** @return string the decimal point character used. */
 547      public function get_point() {
 548          return $this->decsep;
 549      }
 550  
 551      /** @return string the thousands separator character used. */
 552      public function get_separator() {
 553          return $this->thousandssep;
 554      }
 555  
 556      /**
 557       * @return bool If the student's response contains a '.' or a ',' that
 558       * matches the thousands separator in the current locale. In this case, the
 559       * parsing in apply_unit can give a result that the student did not expect.
 560       */
 561      public function contains_thousands_seaparator($value) {
 562          if (!in_array($this->thousandssep, array('.', ','))) {
 563              return false;
 564          }
 565  
 566          return strpos($value, $this->thousandssep) !== false;
 567      }
 568  
 569      /**
 570       * Create the regular expression that {@link parse_response()} requires.
 571       * @return string
 572       */
 573      protected function build_regex() {
 574          if (!is_null($this->regex)) {
 575              return $this->regex;
 576          }
 577  
 578          $decsep = preg_quote($this->decsep, '/');
 579          $thousandssep = preg_quote($this->thousandssep, '/');
 580          $beforepointre = '([+-]?[' . $thousandssep . '\d]*)';
 581          $decimalsre = $decsep . '(\d*)';
 582          $exponentre = '(?:e|E|(?:x|\*|×)10(?:\^|\*\*))([+-]?\d+)';
 583  
 584          $numberbit = "{$beforepointre}(?:{$decimalsre})?(?:{$exponentre})?";
 585  
 586          if ($this->unitsbefore) {
 587              $this->regex = "/{$numberbit}$/";
 588          } else {
 589              $this->regex = "/^{$numberbit}/";
 590          }
 591          return $this->regex;
 592      }
 593  
 594      /**
 595       * This method can be used for more locale-strict parsing of repsonses. At the
 596       * moment we don't use it, and instead use the more lax parsing in apply_units.
 597       * This is just a note that this funciton was used in the past, so if you are
 598       * intersted, look through version control history.
 599       *
 600       * Take a string which is a number with or without a decimal point and exponent,
 601       * and possibly followed by one of the units, and split it into bits.
 602       * @param string $response a value, optionally with a unit.
 603       * @return array four strings (some of which may be blank) the digits before
 604       * and after the decimal point, the exponent, and the unit. All four will be
 605       * null if the response cannot be parsed.
 606       */
 607      protected function parse_response($response) {
 608          if (!preg_match($this->build_regex(), $response, $matches)) {
 609              return array(null, null, null, null);
 610          }
 611  
 612          $matches += array('', '', '', ''); // Fill in any missing matches.
 613          list($matchedpart, $beforepoint, $decimals, $exponent) = $matches;
 614  
 615          // Strip out thousands separators.
 616          $beforepoint = str_replace($this->thousandssep, '', $beforepoint);
 617  
 618          // Must be either something before, or something after the decimal point.
 619          // (The only way to do this in the regex would make it much more complicated.)
 620          if ($beforepoint === '' && $decimals === '') {
 621              return array(null, null, null, null);
 622          }
 623  
 624          if ($this->unitsbefore) {
 625              $unit = substr($response, 0, -strlen($matchedpart));
 626          } else {
 627              $unit = substr($response, strlen($matchedpart));
 628          }
 629          $unit = trim($unit);
 630  
 631          return array($beforepoint, $decimals, $exponent, $unit);
 632      }
 633  
 634      /**
 635       * Takes a number in almost any localised form, and possibly with a unit
 636       * after it. It separates off the unit, if present, and converts to the
 637       * default unit, by using the given unit multiplier.
 638       *
 639       * @param string $response a value, optionally with a unit.
 640       * @return array(numeric, sting) the value with the unit stripped, and normalised
 641       *      by the unit multiplier, if any, and the unit string, for reference.
 642       */
 643      public function apply_units($response, $separateunit = null) {
 644          // Strip spaces (which may be thousands separators) and change other forms
 645          // of writing e to e.
 646          $response = str_replace(' ', '', $response);
 647          $response = preg_replace('~(?:e|E|(?:x|\*|×)10(?:\^|\*\*))([+-]?\d+)~', 'e$1', $response);
 648  
 649          // If a . is present or there are multiple , (i.e. 2,456,789 ) assume ,
 650          // is a thouseands separator, and strip it, else assume it is a decimal
 651          // separator, and change it to ..
 652          if (strpos($response, '.') !== false || substr_count($response, ',') > 1) {
 653              $response = str_replace(',', '', $response);
 654          } else {
 655              $response = str_replace([$this->thousandssep, $this->decsep, ','], ['', '.', '.'], $response);
 656          }
 657  
 658          $regex = '[+-]?(?:\d+(?:\\.\d*)?|\\.\d+)(?:e[-+]?\d+)?';
 659          if ($this->unitsbefore) {
 660              $regex = "/{$regex}$/";
 661          } else {
 662              $regex = "/^{$regex}/";
 663          }
 664          if (!preg_match($regex, $response, $matches)) {
 665              return array(null, null, null);
 666          }
 667  
 668          $numberstring = $matches[0];
 669          if ($this->unitsbefore) {
 670              // Substr returns false when it means '', so cast back to string.
 671              $unit = (string) substr($response, 0, -strlen($numberstring));
 672          } else {
 673              $unit = (string) substr($response, strlen($numberstring));
 674          }
 675  
 676          if (!is_null($separateunit)) {
 677              $unit = $separateunit;
 678          }
 679  
 680          if ($this->is_known_unit($unit)) {
 681              $multiplier = 1 / $this->units[$unit];
 682          } else {
 683              $multiplier = null;
 684          }
 685  
 686          return array($numberstring + 0, $unit, $multiplier); // The + 0 is to convert to number.
 687      }
 688  
 689      /**
 690       * @return string the default unit.
 691       */
 692      public function get_default_unit() {
 693          reset($this->units);
 694          return key($this->units);
 695      }
 696  
 697      /**
 698       * @param string $answer a response.
 699       * @param string $unit a unit.
 700       */
 701      public function add_unit($answer, $unit = null) {
 702          if (is_null($unit)) {
 703              $unit = $this->get_default_unit();
 704          }
 705  
 706          if (!$unit) {
 707              return $answer;
 708          }
 709  
 710          if ($this->unitsbefore) {
 711              return $unit . ' ' . $answer;
 712          } else {
 713              return $answer . ' ' . $unit;
 714          }
 715      }
 716  
 717      /**
 718       * Is this unit recognised.
 719       * @param string $unit the unit
 720       * @return bool whether this is a unit we recognise.
 721       */
 722      public function is_known_unit($unit) {
 723          return array_key_exists($unit, $this->units);
 724      }
 725  
 726      /**
 727       * Whether the units go before or after the number.
 728       * @return true = before, false = after.
 729       */
 730      public function are_units_before() {
 731          return $this->unitsbefore;
 732      }
 733  
 734      /**
 735       * Get the units as an array suitably for passing to html_writer::select.
 736       * @return array of unit choices.
 737       */
 738      public function get_unit_options() {
 739          $options = array();
 740          foreach ($this->units as $unit => $notused) {
 741              $options[$unit] = $unit;
 742          }
 743          return $options;
 744      }
 745  }