lib.php 76 KB
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<?php
/**
 * Mahara: Electronic portfolio, weblog, resume builder and social networking
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 * Copyright (C) 2006-2009 Catalyst IT Ltd and others; see:
 *                         http://wiki.mahara.org/Contributors
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 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @package    mahara
 * @subpackage import-leap
 * @author     Catalyst IT Ltd
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL
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 * @copyright  (C) 2006-2009 Catalyst IT Ltd http://catalyst.net.nz
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 *
 */

defined('INTERNAL') || die();

/**
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 * Implements import of Leap2A files
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 *
 * For more documentation, please see:
 * http://wiki.mahara.org/index.php?title=Developer_Area/Import%2F%2FExport/LEAP_Import
 */
class PluginImportLeap extends PluginImport {

    private $xml = null;
    private $namespaces = array();
    private $strategylisting = array();
    private $loadmapping = array();
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    private $coreloadmapping = array();
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    private $artefactids = array();
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    private $viewids = array();
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    private $collectionids = array();
    private $collectionviewentries = array();
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    protected $filename;
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    protected $persondataid = null;

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    protected $loglevel = 0;
    protected $logtargets = LOG_TARGET_ERRORLOG;
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    protected $logfile = '';
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    protected $profile = false;
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    protected $leap2anamespace = null;
    protected $leap2atypenamespace = null;
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    protected $leap2acategories = null;
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    // the version is stored with the full url since the url might change in
    // future versions (as it has between 2009-03 and 2010-07)
    protected $supportedleap2aversions = array('http://www.leapspecs.org/2010-07/2A/');
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    private $snapshots = array();

    const LOG_LEVEL_STANDARD = 1;
    const LOG_LEVEL_VERBOSE  = 2;

    const NS_ATOM       = 'http://www.w3.org/2005/Atom';
    const NS_RDF        = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#';
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    const NS_LEAP_200903       = 'http://wiki.cetis.ac.uk/2009-03/LEAP2A_predicates#';
    const NS_LEAPTYPE_200903   = 'http://wiki.cetis.ac.uk/2009-03/LEAP2A_types#';
    const NS_CATEGORIES_200903 = 'http://wiki.cetis.ac.uk/2009-03/LEAP2A_categories/';
    const NS_LEAP              = 'http://terms.leapspecs.org/';
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    const NS_CATEGORIES        = 'http://wiki.leapspecs.org/2A/categories/';
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    const NS_MAHARA     = 'http://wiki.mahara.org/Developer_Area/Import%2F%2FExport/LEAP_Extensions#';

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    const XHTML_DIV       = '<div xmlns="http://www.w3.org/1999/xhtml">';
    const XHTML_DIV_EMPTY = '<div xmlns="http://www.w3.org/1999/xhtml"/>';

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    const STRATEGY_IMPORT_AS_VIEW = 1;
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    const STRATEGY_IMPORT_AS_COLLECTION = 2;
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    public static function validate_transported_data(ImporterTransport $transport) {
        $importdata = $transport->files_info();
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        if (!$file = self::find_file($importdata)) {
            throw new ImportException(null, 'Missing leap xml file');
        }
    }

    public static function find_file($importdata) {
        $path = $importdata['tempdir'] . 'extract/';
        if (!empty($importdata['manifestfile'])) {
            $files = array($importdata['manifestfile']);
        } else {
            $files = array('leap.xml', 'leap2.xml', 'leap2a.xml');
        }
        foreach ($files as $f) {
            if (file_exists($path . $f)) {
                return $path . $f;
            }
        }
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    }

    public function get($field) {
        if ($field == 'xml') {
            return $this->xml;
        }
        return parent::get($field);
    }

    public function process() {
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        db_begin();

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        $this->filename = self::find_file($this->get('importertransport')->files_info());
        $this->logfile = dirname($this->filename) . '/import.log';
        $this->trace('Loading import from ' . $this->filename);
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        $this->snapshot('begin');

        $options =
            LIBXML_COMPACT |    // Reported to greatly speed XML parsing
            LIBXML_NONET        // Disable network access - security check
        ;
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        if (function_exists('libxml_disable_entity_loader')) {
            // The LIBXML_NONET stops proper network based XXE attacks from happening
            libxml_disable_entity_loader(false);
        }
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        if (!$this->xml = simplexml_load_file($this->filename, 'SimpleXMLElement', $options)) {
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            // TODO: bail out in a much nicer way...
            throw new ImportException($this, "FATAL: XML file is not well formed! Please consult Mahara's error log for more information");
        }
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        if (function_exists('libxml_disable_entity_loader')) {
            libxml_disable_entity_loader(true);
        }
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        $this->namespaces = array_flip($this->xml->getDocNamespaces());
        $this->registerXpathNamespaces($this->xml);
        $this->trace("Document loaded, entries: " . count($this->xml->entry));
        $this->snapshot('loaded XML');

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        $this->detect_leap2a_namespace();

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        $this->ensure_document_valid();

        $this->create_strategy_listing();
        $this->snapshot('created strategy listing');
        $this->strategy_listing_to_load_mapping();
        $this->snapshot('converted strategy listing to load mapping');
        $this->import_from_load_mapping();
        $this->snapshot('imported data based on load mapping');
        $this->import_completed();

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        db_commit();
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    }

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    /**
     * detect the leap2a namespace of the import document by looking for the 'version' element
     *
     *
     */
    private function detect_leap2a_namespace () {
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        // check for the leap2a version used
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        // disable xml warnings. The initial LEAP2A spec hasn't got the leap2
        // namespace so the following xpath expression triggers a warning
        // which we want to suppress.
        $oldvalue = libxml_use_internal_errors(true);
        $version = $this->xml->xpath('//leap2:version');
        libxml_use_internal_errors($oldvalue);

        // if there is no version string we assume the first version of the
        // LEAP2A spec which doesn't contain the version element
        if(!empty($version) && !in_array($version[0][0], $this->supportedleap2aversions)) {
            throw new ImportException($this, "FATAL: The version of the uploaded LEAP2A file is not supported by this Mahara version");
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        }
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        if($version) {
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            $this->leap2anamespace = self::NS_LEAP;
            $this->leap2atypenamespace = self::NS_LEAP;
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            // this is a workaround for a bug that was introduced during the
            // update to LEAP2A 2010-07. Exports between the update and this
            // bugfix will contain a wrong namespace. This workaround will
            // allow those exports to still import properly. (bug #673434)
            if (isset($this->namespaces['http://wiki.leapspecs.org/2A/categories'])) {
                $this->leap2acategories = 'http://wiki.leapspecs.org/2A/categories';
            } else {
                $this->leap2acategories = self::NS_CATEGORIES;
            }
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        } else {
            $this->leap2anamespace = self::NS_LEAP_200903;
            $this->leap2atypenamespace = self::NS_LEAPTYPE_200903;
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            $this->leap2acategories = self::NS_CATEGORIES_200903;
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        }
    }

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    private function ensure_document_valid() {
        // TODO: http://wiki.mahara.org/Developer_Area/Import%2f%2fExport/Import%3a_Implementation_Plan#beginning
        //
        // Do a bunch of checks that will ensure the feed is valid, and thus 
        // allow future code to make assumptions that the feed is valid

        // Things to check:
        // - all content src="X": make sure the src actually exists
        // - feed has a <feed> element with an <author> and <entry>s
        // - feed element has correct namespaces (keep in mind we need to be 
        // able to import raw ATOM feeds too)

        //throw new ImportException($this, "Import wasn't valid. TODO: error reporting");
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        // Check all the namespaces we're gonna need are declared, and warn if 
        // they're not there
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        if($this->leap2anamespace == self::NS_LEAP) {
            $namespaces = array(self::NS_ATOM, self::NS_RDF, self::NS_LEAP, self::NS_CATEGORIES);
        } else {
            $namespaces = array(self::NS_ATOM, self::NS_RDF, self::NS_LEAP_200903, self::NS_LEAPTYPE_200903, self::NS_CATEGORIES_200903);
        }
        foreach ($namespaces as $ns) {
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            if (!isset($this->namespaces[$ns])) {
                $this->trace("WARNING: Namespaces $ns wasn't declared - this will make importing data correctly difficult");
            }
        }
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    }

    /**
     * http://wiki.mahara.org/Developer_Area/Import%2f%2fExport/Import%3a_Implementation_Plan#first_pass_-_get_scores_from_plugins_for_each_entry
     *
     * Each list of strategies for each entry should be sorted from highest to lowest score once this is done
     */
    private function create_strategy_listing() {
        $this->trace("-------------------------\ncreate_strategy_listing()");
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        // Give all plugins a chance to perform setup tasks
        foreach (plugins_installed('artefact') as $plugin) {
            $plugin = $plugin->name;
            if (safe_require('import', 'leap/' . $plugin, 'lib.php', 'require_once', true)) {
                $classname = 'LeapImport' . ucfirst($plugin);
                if (method_exists($classname, 'setup')) {
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                    safe_require('artefact', $plugin);
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                    call_static_method($classname, 'setup', $this);
                }
            }
        }
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        // First, try to establish whether there is an element representing the 
        // author of the feed
        // TODO: also check this element has the right leaptype (person)
        if (is_null($this->persondataid)) {
            $author = $this->get('xml')->xpath('//a:feed/a:author[1]');
            $author = $author[0];
            if (isset($author->uri) && $this->get_entry_by_id((string)$author->uri)) {
                $this->persondataid = (string)$author->uri;
            }
            else {
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                $persondata = $this->get('xml')->xpath('//a:feed/a:entry/a:category[('
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                    . $this->curie_xpath('@scheme', $this->get_categories_namespace(), 'person_type#') . ') and @term="Self"]/../a:id');
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                if (isset($persondata[0])) {
                    $this->persondataid = (string)$persondata[0][0];
                }
                else {
                    $this->persondataid = false;
                }
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            }
        }

        // Generate strategy listing
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        foreach ($this->xml->xpath('//a:feed/a:entry') as $entry) {
            $this->registerXpathNamespaces($entry);
            $entryid = (string)$entry->id;
            $this->trace(" * $entryid ({$entry->title})");

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            if ($this->persondataid && $entryid == $this->persondataid) {
                // We don't offer this element to any plugin to be imported
                continue;
            }

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            foreach (plugins_installed('artefact') as $plugin) {
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                $plugin = $plugin->name;
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                $classname = 'LeapImport' . ucfirst($plugin);
                if (class_exists($classname)) {
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                    if (!is_subclass_of($classname, 'LeapImportArtefactPlugin')) {
                        throw new SystemException("Class $classname does not extend LeapImportArtefactPlugin as it should");
                    }
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                    if (method_exists($classname, 'get_import_strategies_for_entry')) {
                        $strategies = call_static_method($classname, 'get_import_strategies_for_entry', $entry, $this);
                        $this->trace("   artefact.$plugin strategies: " . count($strategies));
                        if ($strategies) {
                            $this->trace($strategies, self::LOG_LEVEL_VERBOSE);
                            foreach ($strategies as $strategy) {
                                // Verify they're in valid form
                                if (!array_key_exists('strategy', $strategy)
                                    || !array_key_exists('score', $strategy)
                                    || !array_key_exists('other_required_entries', $strategy)) {
                                    throw new SystemException("$classname::get_import_strategies_for_entry returned a strategy missing "
                                        . "one or more of the strategy, score or other_required_entries keys");
                                }
                                $strategy['artefactplugin'] = $plugin;
                                $this->strategylisting[$entryid][] = $strategy;
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                            }
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                        }
                    }
                }
            }

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            $strategies = $this->get_import_strategies_for_entry($entry);
            $this->trace("   core strategies: " . count($strategies));
            if ($strategies) {
                $this->trace($strategies, self::LOG_LEVEL_VERBOSE);
                foreach ($strategies as $strategy) {
                    $strategy['artefactplugin'] = null;
                    $this->strategylisting[$entryid][] = $strategy;
                }
            }

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            if (!isset($this->strategylisting[$entryid])) {
                $this->trace(" ** Could not find any strategies for $entryid **");
                // TODO: we might need to expose this information later
                continue;
            }

            // Sort by score descending
            usort($this->strategylisting[$entryid], create_function('$a, $b', 'return $a["score"] < $b["score"];'));
        }
        $this->trace('*** Strategy listing: ***');
        $this->trace($this->strategylisting);
    }

    /**
     * Converts a strategy listing into the "best" load mapping that can be 
     * gleaned from the strategy listing.
     *
     * The best mapping is decided by sorting the strategy listing by score and 
     * importing all entries on a first-met, first used basis. The algorithm is 
     * described at:
     * http://wiki.mahara.org/Developer_Area/Import%2f%2fExport/Import%3a_Implementation_Plan#non-interactive_import
     */
    private function strategy_listing_to_load_mapping() {
        $this->trace("----------------------------------\nstrategy_listing_to_load_mapping()");
        $usedlist = array();

        // Each entry has its strategies sorted from best to worst score, then 
        // we sort the entire list of entries by the best scores they have 
        // available. This is so we get the "best" plan for importing
        uasort($this->strategylisting, array($this, 'strategy_listing_sort'));
        $this->trace('*** Sorted strategy listing ***', self::LOG_LEVEL_VERBOSE);
        $this->trace($this->strategylisting, self::LOG_LEVEL_VERBOSE);

        // We're only interested in the first listing really. It's the strategy 
        // with the highest score for this entry. Most of the loop mechanics is 
        // so that if we choose to import an entry that requires other entries, 
        // we don't import those other entries separately as well.
        foreach($this->strategylisting as $entryid => $strategies) {
            foreach ($strategies as $strategydata) {
                $this->trace("entry: $entryid");
                if (in_array($entryid, $usedlist)) {
                    $this->trace(" * already in used list, skipped");
                    continue;
                }
                if (isset($strategydata['other_required_entries'])) {
                    foreach ($strategydata['other_required_entries'] as $otherentryid) {
                        if (in_array($otherentryid, $usedlist)) {
                            $this->trace(" * other required entry $otherentryid already in used list, skipped");
                            continue;
                        }
                    }
                }

                $this->trace(" * using strategy $strategydata[strategy] from plugin $strategydata[artefactplugin]");
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                if ($strategydata['artefactplugin']) {
                    $this->loadmapping[$entryid] = $strategydata;
                }
                else {
                    $this->coreloadmapping[$entryid] = $strategydata;
                }
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                $usedlist[] = $entryid;

                if (isset($strategydata['other_required_entries'])) {
                    foreach ($strategydata['other_required_entries'] as $otherentryid) {
                        $usedlist[] = $otherentryid;
                    }
                }

                // We've found how we're going to import this entry now
                // TODO: we should check the next strategy here and see if it 
                // has the same score, if it does we should note that for later 
                // for debugging purposes
                break;
            }
        }
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        $this->trace("*** Plugin load mapping: ***");
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        $this->trace($this->loadmapping);
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        $this->trace("*** Core load mapping: ***");
        $this->trace($this->coreloadmapping);
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    }

    private function strategy_listing_sort($a, $b) {
        // NOTE: the strategy listing should already have the strategies for 
        // each entry sorted from highest to lowest score. If it doesn't, these 
        // two sorts fix that, but this should never happen.
        //usort($a, create_function('$a, $b', 'return $a["score"] < $b["score"];'));
        //usort($b, create_function('$a, $b', 'return $a["score"] < $b["score"];'));
        return $a[0]['score'] < $b[0]['score'];
    }

    /**
     * Import entries using our load mapping. See:
     * http://wiki.mahara.org/Developer_Area/Import%2f%2fExport/Import%3a_Implementation_Plan#second_pass.3a_load_all_entries_into_mahara_as_per_load_mapping
     */
    private function import_from_load_mapping() {
        $this->trace("--------------------------\nimport_from_load_mapping()");
        // TODO: do both usedlists as by key instead of by value for faster checks
        $usedlist = $loadedentries = array();
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        uasort($this->loadmapping, create_function('$a, $b', 'return $a["score"] < $b["score"];'));
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        foreach ($this->loadmapping as $entryid => $strategydata) {
            if (in_array($entryid, $usedlist)) {
                $this->trace("WARNING: $entryid has already been imported as part of a previous entry");
                continue;
            }
            if (isset($strategydata['other_required_entries'])) {
                foreach ($strategydata['other_required_entries'] as $otherentryid) {
                    if (in_array($otherentryid, $usedlist)) {
                        $this->trace("WARNING: $entryid has already been imported as part of a previous entry");
                        continue(2);
                    }
                }
            }

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            $this->trace("Importing $entryid using strategy $strategydata[strategy] of plugin $strategydata[artefactplugin]");
            safe_require('artefact', $strategydata['artefactplugin']);
            $entry = $this->get_entry_by_id($entryid);
            $classname = 'LeapImport' . ucfirst($strategydata['artefactplugin']);
            // TODO: this throws ImportException if it can't be imported, need
            // to decide if this exception can bubble up or whether it should
            // be caught here
            $artefactmapping = call_static_method($classname, 'import_using_strategy',
                $entry, $this, $strategydata['strategy'], $strategydata['other_required_entries']);
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            if (!is_array($artefactmapping)) {
                throw new SystemException("import_from_load_mapping(): $classname::import_using_strategy has not return a list");
            }

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            $this->artefactids = array_merge_recursive($this->artefactids, $artefactmapping);
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            $usedlist[] = $entryid;
            if (isset($strategydata['other_required_entries'])) {
                foreach ($strategydata['other_required_entries'] as $otherentryid) {
                    $usedlist[] = $otherentryid;
                }
            }

            $loadedentries[] = $entryid;
        }

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        // Give plugins a chance to import stuff about the feed author from the 
        // persondata entry
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        // TODO: this should return an artefact mapping so things can create 
        // links to profile fields, but nothing actually needs it yet
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        if (!is_array($this->data) || !array_key_exists('skippersondata', $this->data) || $this->data['skippersondata'] !== true) {
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            foreach (plugins_installed('artefact') as $plugin) {
                $classname = 'LeapImport' . ucfirst($plugin->name);
                if (method_exists($classname, 'import_author_data')) {
                    call_static_method($classname, 'import_author_data', $this, $this->persondataid);
                }
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            }
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        }
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        // Now all artefacts are loaded, allow each plugin to load 
        // relationships for them if they need to
        foreach ($loadedentries as $entryid) {
            $strategydata = $this->loadmapping[$entryid];
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            $classname = 'LeapImport' . ucfirst($strategydata['artefactplugin']);
            $entry = $this->get_entry_by_id($entryid);
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            $maybeartefacts = call_static_method($classname, 'setup_relationships',
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                $entry, $this, $strategydata['strategy'], $strategydata['other_required_entries']);
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            if (is_array($maybeartefacts)) { // some might add new artefacts (eg files attached by relpath, rather than leap id)
                $this->artefactids = array_merge_recursive($this->artefactids, $maybeartefacts);
            }
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        }

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        // Fix up any artefact references in the content of imported artefacts
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        // TODO: restrict this to the ones that were imported right now
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        if ($artefacts = get_records_array('artefact', 'owner', $this->get('usr'), '', 'id, title, description')) {
            foreach ($artefacts as $artefact) {
                $this->fix_artefact_references($artefact);
            }
        }

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        // Now import views
        foreach ($this->coreloadmapping as $entryid => $strategydata) {
            if (in_array($entryid, $usedlist)) {
                $this->trace("WARNING: $entryid has already been imported as part of a previous entry");
                continue;
            }
            if (isset($strategydata['other_required_entries'])) {
                foreach ($strategydata['other_required_entries'] as $otherentryid) {
                    if (in_array($otherentryid, $usedlist)) {
                        $this->trace("WARNING: $entryid has already been imported as part of a previous entry");
                        continue(2);
                    }
                }
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            }
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            $this->trace("Importing $entryid using the core");
            $entry = $this->get_entry_by_id($entryid);
            $this->import_using_strategy($entry, $strategydata['strategy'], $strategydata['other_required_entries']);

            $usedlist[] = $entryid;
            if (isset($strategydata['other_required_entries'])) {
                foreach ($strategydata['other_required_entries'] as $otherentryid) {
                    $usedlist[] = $otherentryid;
                }
            }

            $loadedentries[] = $entryid;
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        }
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        // Put views into collections
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        // Keep track of which views have been placed in a collection, because
        // Mahara can't handle more one collection per view.
        $incollection = array();

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        foreach ($this->collectionviewentries as $cid => $entryids) {
            $i = 0;
            foreach ($entryids as $entryid) {
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                $viewid = self::get_viewid_imported_by_entryid($entryid);
                if ($viewid && !isset($incollection[$viewid])) {
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                    $record = (object) array(
                        'collection' => $cid,
                        'view' => $viewid,
                        'displayorder' => $i,
                    );
                    insert_record('collection_view', $record);
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                    $incollection[$viewid] = $cid;
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                    $i++;
                }
            }
        }

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        // Allow each plugin to load relationships to views if they need to
        foreach ($loadedentries as $entryid) {
            if (isset($this->loadmapping[$entryid])) {
                $strategydata = $this->loadmapping[$entryid];
                $classname = 'LeapImport' . ucfirst($strategydata['artefactplugin']);
                $entry = $this->get_entry_by_id($entryid);
                call_static_method($classname, 'setup_view_relationships',
                    $entry, $this, $strategydata['strategy'], $strategydata['other_required_entries']);
            }
        }
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    }

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    public function entry_has_strategy($entryid, $strategyid, $artefactplugin=null) {
        if (isset($this->loadmapping[$entryid])) {
            if (empty($this->loadmapping[$entryid]['artefactplugin']) && !empty($artefactplugin)) {
                return false;
            }
            if ($this->loadmapping[$entryid]['artefactplugin'] != $artefactplugin) {
                return false;
            }
            return $this->loadmapping[$entryid]['strategy'] == $strategyid;
        }
        return false;
    }

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    private function import_completed() {
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        // Give all plugins a chance to perform final tasks
        foreach (plugins_installed('artefact') as $plugin) {
            $classname = 'LeapImport' . ucfirst($plugin->name);
            if (method_exists($classname, 'cleanup')) {
                call_static_method($classname, 'cleanup', $this);
            }
        }
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        $this->trace("------------------\nimport_completed()");

        unset($this->loadmapping);
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        unset($this->coreloadmapping);
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        unset($this->strategylisting);
        unset($this->xpath);
        unset($this->dom);
        $this->snapshot('end');

        if ($this->profile) {
            $this->trace("k: abstime\ttime\tmemafter\tmemdiff");
            $firstdata = $lastdata = $this->snapshots['begin'];
            $i = 0;
            foreach ($this->snapshots as $identifier => $data) {
                $i++;
                $timetaken = $data['time'] - $lastdata['time'];
                $abstime   = $data['time'] - $firstdata['time'];
                $memoryafter = $data['ram'] / 1024;
                $memorygrowth = ($data['ram'] - $lastdata['ram']) / 1024;
                $this->trace(sprintf("$i: %.3f\t%.3f\t%.3fK\t%8.3fK", $abstime, $timetaken, $memoryafter, $memorygrowth));
                $lastdata = $data;
            }

            $i = 0;
            foreach (array_keys($this->snapshots) as $identifier) {
                $i++;
                $this->trace("$i = $identifier");
            }
            $this->trace("abstime = time after beginning step of import that this step completed\n"
                . "time = time taken to complete this step\n"
                . "memafter = script memory usage after this step\n"
                . "memdiff = difference in memory usage compared with the last step");
        }
    }

    /**
     * Logs a message for debugging purposes
     *
     * The user can configure the amount of logging, and where it goes, by 
     * setting the 'loglevel' and 'logtargets' fields.
     *
     * loglevel is one of {0, PluginImportLeap::LOG_LEVEL_STANDARD, PluginImportLeap::LOG_LEVEL_VERBOSE}
     * logtargets is one of the LOG_TARGET_* constants
     *
     * @param string $message The message to log
     * @param int    $level   The level at which to log this error
     */
    public function trace($message, $level=self::LOG_LEVEL_STANDARD) {
        if ($level <= $this->loglevel) {
            // Use our logging system temporarily, which provides us with 
            // access to its nice features. We use log_message instead of
            // log_debug because that will retain the the line/file where 
            // trace() was called, rather than saying all of the messages came 
            // from trace() itself
            global $CFG;
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            $oldtargets = $CFG->log_dbg_targets;
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            $oldfile = isset($CFG->log_file) ? $CFG->log_file : null;
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            $CFG->log_dbg_targets = $this->logtargets;
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            $CFG->log_file = $this->logfile;
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            $file = $line = $trace = null;
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            log_message($message, LOG_LEVEL_DBG, true, true, $file, $line, $trace);
            $CFG->log_dbg_targets = $oldtargets;
            $CFG->log_file = $oldfile;
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        }
    }

    private function snapshot($identifier) {
        if ($this->profile) {
            $this->snapshots[$identifier] = array(
                'time' => microtime(true),
                'ram'  => memory_get_usage(), // TODO: http://php.net/memory_get_usage suggests this isn't available everywhere
            );
        }
    }

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    /**
     * Given an entry, should return a list of the possible ways that it could 
     * be imported by the core.
     *
     * The core handles View importing, so this method looks for entries that 
     * could be converted into Views.
     *
     * For more information about this method, see 
     * {LeapImportArtefactPlugin::get_import_strategies_for_entry}
     *
     * @param SimpleXMLElement $entry
     */
    public function get_import_strategies_for_entry(SimpleXMLElement $entry) {
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        if (self::is_rdf_type($entry, $this, 'selection')) {
            if (self::is_correct_category_scheme($entry, $this, 'selection_type', 'Webpage')) {
                return array(array(
                    'strategy' => self::STRATEGY_IMPORT_AS_VIEW,
                    'score'    => 100,
                    'other_required_entries' => array(),
                ));
            }
            if (self::is_correct_category_scheme($entry, $this, 'selection_type', 'Website')) {
                return array(array(
                    'strategy' => self::STRATEGY_IMPORT_AS_COLLECTION,
                    'score'    => 100,
                    'other_required_entries' => array(),
                ));
            }
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        }
        return array();
    }

    /**
     */
    public function import_using_strategy(SimpleXMLElement $entry, $strategy, array $otherentries) {
        switch ($strategy) {
        case self::STRATEGY_IMPORT_AS_VIEW:
            require_once('view.php');

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            if (!$this->import_entry_as_mahara_view($entry)) {
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                // Not a Mahara view, just do basic import
                $this->trace('Not a Mahara view, doing basic import', self::LOG_LEVEL_VERBOSE);

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                $viewdata = array(
                    'title'       => (string)$entry->title,
                    'description' => (string)$entry->summary,
                    'type'        => 'portfolio', // TODO
                    'layout'      => null, // TODO
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                    'tags'        => self::get_entry_tags($entry),
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                    'numrows'     => 1,
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                    'ownerformat' => FORMAT_NAME_DISPLAYNAME, // TODO
                    'owner'       => $this->get('usr'),
                );
                if ($published = strtotime((string)$entry->published)) {
                    $viewdata['ctime'] = $published;
                }
                if ($updated = strtotime((string)$entry->updated)) {
                    $viewdata['mtime'] = $updated;
                }

                $view = View::create($viewdata, $this->get('usr'));
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                safe_require('blocktype', 'textbox');
                $bi = new BlockInstance(0,
                    array(
                        'blocktype'  => 'textbox',
                        'title'      => '',
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                        'row'        => 1,
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                        'column'     => 1,
                        'order'      => 1,
                        'configdata' => array(
                            'text' => self::get_entry_content($entry, $this),
                        ),
                    )
                );
                $view->addblockinstance($bi);
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                $this->viewids[(string)$entry->id] = $view->get('id');
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            }
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            break;
        case self::STRATEGY_IMPORT_AS_COLLECTION:
            require_once('collection.php');

            $collectiondata = array(
                'name'        => (string)$entry->title,
                'description' => (string)$entry->summary,
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                'tags'        => self::get_entry_tags($entry),
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                'owner'       => $this->get('usr'),
            );
            if ($published = strtotime((string)$entry->published)) {
                $collectiondata['ctime'] = $published;
            }
            if ($updated = strtotime((string)$entry->updated)) {
                $collectiondata['mtime'] = $updated;
            }

            $collection = new Collection(0, $collectiondata);
            $collection->commit();
            $this->collectionids[(string)$entry->id] = $collection->get('id');

            // Remember entry ids that form part of this entry, and use them later
            // to put views into collections.
            foreach ($entry->link as $link) {
                if ($this->curie_equals($link['rel'], '', 'has_part') && isset($link['href'])) {
                    $this->collectionviewentries[$collection->get('id')][] = (string) $link['href'];
                }
            }

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            break;
        default:
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            throw new ImportException($this, 'TODO: get_string: unknown strategy chosen for importing entry');
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        }
    }

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    /**
     * Attempts to import an entry as a mahara view
     *
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     * We look for custom mahara namespaced tags that explain the View 
     * structure. If they're present, we use them to create a View using that 
     * structure.
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     *
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     * This differs a bit from the Leap2A specification, but we do so 
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     * deliberately to get 100% compatibility with Mahara to Mahara exports. 
     * Other systems can also construct content in the right format to trigger 
     * Mahara to import things as a full view.
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     *
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     * If the mahara tags are not present, we give up.
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     *
     * @param SimpleXMLElement $entry The entry to be imported
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     * @return boolean Whether it could be imported.
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     */
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    private function import_entry_as_mahara_view(SimpleXMLElement $entry) {
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        static $blocktypes_installed = null;
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        static $columnlayouts = null;
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        static $viewtypes = null;
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        $viewelement = $entry->xpath('mahara:view[1]');
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        if (count($viewelement) != 1) {
            // This isn't a Mahara view
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            return false;
        }

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        if (is_null($columnlayouts)) {
            $columnlayouts = get_records_assoc('view_layout_columns');
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        }
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        if (is_null($viewtypes)) {
            $viewtypes = get_column('view_type', 'type');
        }
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        $maharaattributes = PluginImportLeap::get_attributes($viewelement[0], PluginImportLeap::NS_MAHARA);

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        $type = 'portfolio';
        if (isset($maharaattributes['type']) && in_array($maharaattributes['type'], $viewtypes)) {
            $type = $maharaattributes['type'];
        }
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        $ownerformat = intval($maharaattributes['ownerformat']);
        if (!$ownerformat) {
            $ownerformat = FORMAT_NAME_DISPLAYNAME;
        }

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        $rows = $entry->xpath('mahara:view[1]/mahara:row');
        $rowcount = count($rows);
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        // A flag that indicates whether this is an old-style one-row layout, or a new-style multi-row layout
        $onerowlayout = false;
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        if ($rowcount < 1 || $rowcount > View::$maxlayoutrows) {
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            // Check for a pre-1.8 (one-row) layout
            $columns = $entry->xpath('mahara:view[1]/mahara:column');
            $columncount = count($columns);
            if ($columncount < 1 || $columncount > 5) {
                // Whoops, invalid number of rows
                $this->trace("Invalid number of rows specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                return false;
            }
            else {
                $onerowlayout = true;
                $rows = array($columns);
                $rowcount = 1;
            }
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        }

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        $layout = null;
        if (isset($maharaattributes['layout'])) {
            $rowwidths = explode('-', $maharaattributes['layout']);
            if (count($rowwidths) != $rowcount) {
                $this->trace("Row widths and number of rows do not match for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                return false;
            }
            $columnids = array();
            foreach ($columnlayouts as $columnlayout) {
                foreach ($rowwidths as $key => $widths) {
                    if ($columnlayout->widths == $widths) {
                        $columnids[$key+1] = $columnlayout->id;
                    }
                }
            }
            if (count($columnids) != $rowcount) {
                $this->trace("Invalid row widths were specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                return false;
            }
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            $rowscolssql = '';
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            for ($i=0; $i<count($columnids); $i++) {
                $rowscolssql .= '(row = ' . ($i+1) . ' AND columns = ' . $columnids[$i+1] . ')';
                if ($i != (count($columnids)-1)) {
                    $rowscolssql .= ' OR ';
                }
            }

            // search in default layout options for a match
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            // this will return first possible match with exact match (if any)
            // at front of possibles. More than one possible match can occur
            // if there are 3 or more rows in leap2a layout and 2 of those rows
            // match more than one possible view layout.
            $sql = 'SELECT vlrc.viewlayout AS id
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                    FROM
                        {view_layout} vl
                        INNER JOIN {view_layout_rows_columns} vlrc
                            ON vl.id = vlrc.viewlayout
                        INNER JOIN (
                            SELECT
                                viewlayout, COUNT(*)
                            FROM {view_layout_rows_columns}
                            GROUP BY viewlayout
                            HAVING COUNT(*) = ?
                        ) vlrc2
                            ON vlrc.viewlayout = vlrc2.viewlayout
                        INNER JOIN {usr_custom_layout} ucl
                            ON ucl.layout = vl.id
                    WHERE (' . $rowscolssql . ')
                        AND (
                            vl.iscustom = 0
                            OR (
                                vl.iscustom = 1 AND ucl.usr = ?
                            )
                        )
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                    GROUP BY vlrc.viewlayout
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                    HAVING count(*) = ?
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                    LIMIT 1';
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            $layout = get_record_sql($sql, array($rowcount, $this->get('usr'), $rowcount));
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            if (!$layout) {
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                require_once(get_config('docroot') . 'lib/layoutpreviewimage.php');
                // No existing layout matches their page. This probably means they used a custom layout. So, create a new custom layout for them.

                // First check to see whether the custom layout they're using is acceptable in our system
                // TODO: A clever way to squeeze their page into one of the standard layouts if it isn't acceptable.
                // Maybe just put everything into a one-column layout and let them rearrange it?
                if (count ($rowwidths) < 1 || count($rowwidths) > View::$maxlayoutrows) {
                    $this->trace("Invalid layout specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                    return false;
                }

                $i = 1;
                $layoutdata = array();
                $layoutdata['numrows'] = count($rowwidths);
                foreach ($rowwidths as $row) {
                    // First, check to see whether this row matches a valid row layout in the DB
                    $rowcolid = get_field('view_layout_columns', 'id', 'widths', $row);
                    if (!$rowcolid) {
                        $this->trace("Invalid layout specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                        return false;
                    }

                    // Data to help us generate the layout
                    $layoutdata["row{$i}"] = $rowcolid;
                    $i++;
                }

                // Now that we know the layout is valid, generate a record and a thumbnail image for it.
                db_begin();
                // An empty view object, since this view isn't present in the DB yet. We need this in order to access the layout methods
                $viewobj = new View(0, array(
                    'owner' => $this->get('usr'),
                    'deleted' => true // To prevent it from being stored in the DB by the View destructor
                ));
                $layoutresult = $viewobj->addcustomlayout($layoutdata);
                if (empty($layoutresult['layoutid'])) {
                    $this->trace("Invalid layout specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                    db_rollback();
                    return false;
                }
                else {
                    $viewobj->updatecustomlayoutpreview($layoutdata);
                    $layout = (object) array('id' => $layoutresult['layoutid']);
                    db_commit();
                }
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            }
        }

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        $config = array(
            'title'       => (string)$entry->title,
            'description' => (string)$entry->summary,
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            'type'        => $type,
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            'layout'      => $layout->id,
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            'tags'        => self::get_entry_tags($entry),
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            'numrows'      => $rowcount,
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            'owner'       => $this->get('usr'),
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            'ownerformat' => $ownerformat,
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        );
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        $rowindex = 1;
        foreach ($rows as $row) {
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            // If this is the old one-row layout, we'll have handled that earlier, and have the one row's columns be in $columns
            if (!$onerowlayout) {
                $columns = $row->xpath('mahara:column');
                $columncount = count($columns);
                if ($columncount < 1 || $columncount > 5) {
                    // Whoops, invalid number of columns
                    $this->trace("Invalid number of columns specified for potential view {$entry->id}, falling back to standard import", self::LOG_LEVEL_VERBOSE);
                    return false;
                }
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            }
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            $colindex = 1;
            foreach ($columns as $column) {
                $blockinstances = $column->xpath('mahara:blockinstance');
                $order = 1;
                $config['rows'][$rowindex]['columns'][$colindex] = array();
                foreach ($blockinstances as $blockinstance) {
                    $attrs = self::get_attributes($blockinstance, PluginImportLeap::NS_MAHARA);
                    if (!isset($attrs['blocktype'])) {
                        $this->trace("  No mahara:blocktype attribute set for blockinstance at row $rowindex col $colindex, order $order: skipping");
                        continue;
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                    }
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                    $this->trace("  Found block with type {$attrs['blocktype']} at [$rowindex][$colindex][$order]", self::LOG_LEVEL_VERBOSE);
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                    if ($blocktypes_installed === null) {
                        $blocktypes_installed = array_map(create_function('$a', 'return $a->name;'), plugins_installed('blocktype'));
                    }

                    if (in_array($attrs['blocktype'], $blocktypes_installed)) {
                        $configelements = $blockinstance->xpath('mahara:*');
                        $config['rows'][$rowindex]['columns'][$colindex][$order] = array(
                            'type'   => $attrs['blocktype'],
                            'title'  => $attrs['blocktitle'],
                            'config' => array()
                        );
                        foreach ($configelements as $element) {
                            $value = json_decode((string)$element);
                            if (is_array($value) && isset($value[0])) {
                                $config['rows'][$rowindex]['columns'][$colindex][$order]['config'][$element->getName()] = $value[0];
                            }
                            else {
                                $this->trace("  Value for {$element->getName()} is not an array, ignoring (value follows below)");
                                $this->trace($value);
                            }
                        }

                        $order++;
                    }
                    else {
                        $this->trace("  Ignoring unknown blocktype {$attrs['blocktype']}");
                    }
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                }
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                $colindex++;
            } // cols
            $rowindex++;
        } //rows
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        $view = View::import_from_config($this->rewrite_artefact_ids($config), $this->get('usr'), 'leap');
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        if ($published = strtotime((string)$entry->published)) {
            $view->set('ctime', $published);
        }
        if ($updated = strtotime((string)$entry->updated)) {
            $view->set('mtime', $updated);
        }
        $view->set('owner', $this->get('usr'));

        $view->commit();
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        $this->viewids[(string)$entry->id] = $view->get('id');
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        return true;
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    }

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    /**
     * Given the view config that we have built from the export, rewrite all
     * the entry references in blockinstance artefactid fields to be actual
     * artefact IDs.
     */
    private function rewrite_artefact_ids($config) {
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        foreach ($config['rows'] as &$row) {
            foreach ($row['columns'] as &$column) {
                foreach ($column as &$blockinstance) {
                    if (isset($blockinstance['config']['artefactid'])) {
                        $artefactid = $blockinstance['config']['artefactid'];
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                        if (isset($this->artefactids[$artefactid])) {
                            if (count($this->artefactids[$artefactid]) == 1) {
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                                $blockinstance['config']['artefactid'] = intval($this->artefactids[$artefactid][0]);
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                            }
                            else {
                                $this->trace('WARNING: View config specified one artefact, but loadmapping says more than one artefact was loaded for ' . $artefactid);
                                $this->trace($this->artefactids[$artefactid]);
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                                unset($blockinstance['config']['artefactid']);
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                            }
                        }
                        else {
                            $this->trace('WARNING: View config specified an artefact, but loadmapping does not say one was loaded for '. $artefactid);
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                            unset($blockinstance['config']['artefactid']);
                        }
                    }
                    else if (isset($blockinstance['config']['artefactids'])) {
                        $ids = $blockinstance['config']['artefactids'];
                        foreach ($blockinstance['config']['artefactids'] as $key => $artefactid) {
                            if (isset($this->artefactids[$artefactid])) {
                                if (count($this->artefactids[$artefactid]) == 1) {
                                    $blockinstance['config']['artefactids'][$key] = intval($this->artefactids[$artefactid][0]);
                                }
                                else {
                                    $this->trace('WARNING: View config specified one artefact, but loadmapping says more than one artefact was loaded for ' . $artefactid);
                                    $this->trace($this->artefactids[$artefactid]);
                                    unset($blockinstance['config']['artefactids'][$key]);
                                }
                            }
                            else {
                                $this->trace('WARNING: View config specified an artefact, but loadmapping does not say one was loaded for '. $artefactid);
                                unset($blockinstance['config']['artefactids'][$key]);
                            }
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                        }
                    }
                }
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            } // cols
        } // rows
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        return $config;
    }

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    /**
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     * Given an artefact record, looks through it for any Leap2A style
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     * references to other artefacts, and rewrite those to point at the created
     * ones.
     *
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     * @param object $artefact A record from the artefact table (only id, title,
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     *                        description fields required)
     */
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    private function fix_artefact_references($artefact) {
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        $changed = false;

        if ($this->artefact_reference_quickcheck($artefact->title)) {
            if ($title = $this->fix_artefact_reference($artefact->title)) {
                $changed = true;
                $artefact->title = $title;
            }
        }

        if ($this->artefact_reference_quickcheck($artefact->description)) {
            if ($description = $this->fix_artefact_reference($artefact->description)) {
                $changed = true;
                $artefact->description = $description;
            }
        }

        if ($changed) {
            update_record('artefact', $artefact);
        }

    }

    /**
     * Detect whether it's worth running the potentially costly regex
     * replacements and content updates when fixing artefact references
     *
     * @param string   The field to check
     * @return boolean Whether it's worth checking in more detail
     */
    private function artefact_reference_quickcheck($field) {
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        $ns = $this->namespaces[$this->leap2anamespace];
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        return (false !== strpos($field, 'rel="'.$ns.':has_part"')
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                || false !== strpos($field, 'rel="enclosure"'))
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            && (
                (false !== strpos($field, '<img'))
                || (false !== strpos($field, '<a'))
               );
    }

    /**
     * Fix up references to artefacts in a field
     *
     * @param string $field The field to fix
     * @return string The fixed field
     */
    private function fix_artefact_reference($field) {
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        $ns = $this->namespaces[$this->leap2anamespace];

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        // load the field as XML
        $dom = new DOMDocument('1.0', 'utf-8');
        $dom->loadHTML($field);
        $xml = simplexml_import_dom($dom);

        // and search for <img> and <a> tags
        $elements = $xml->xpath('//img|//a');

        // loop through all elements found
        foreach ($elements as $e) {
            $rel  = (string)$e->attributes()->rel;
            $name = (string)$e->getName();
            $href = $e->attributes()->href;
            $src  = $e->attributes()->src;

            // identified as fixable?
            if ($rel == $ns . ':has_part' || $rel == 'enclosure') {
                // change the href / src attributes
                if (isset($href)) {
                    $value = $this->_fixref((string)$href);
                }
                else if (isset($src)) {
                    $value = $this->_fixref((string)$src);
                }

                if (isset($value)) {
                    switch ($name) {
                        case 'a':
                            if (isset($e->attributes()->href)) {
                                $e->attributes()->href = $value;
                            }
                            else {
                                $e->addAttribute('href', $value);
                            }
                            break;
                        case 'img':
                            if (isset($e->attributes()->src)) {
                                $e->attributes()->src = $value;
                            }
                            else {
                                $e->addAttribute('src', $value);
                            }
                            break;
                    }

                    // remove the 'rel' attribute
                    unset($e->attributes()->rel);
                }
            }
        }

        // DOMDocument wraps the content with '<html><body></body></html>'
        // so we call children() twice to remove it again
        return $xml->children()->children()->asXML();
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    }

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    private function _fixref($hrefsrc) {
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        static $basepath;
        if (!$basepath) {
            $basepath = get_mahara_install_subdirectory();
        }

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        $artefacts = $this->get_artefactids_imported_by_entryid($hrefsrc);
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        if (is_null($artefacts) || count($artefacts) != 1) {
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            // This can happen if a Leap2A xml file is uploaded that refers to
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            // files that (naturally) weren't uploaded with it.
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            log_debug("Warning: fixref was expecting one artefact to have been imported by entry {$hrefsrc} but seems to have gotten " . count($artefacts));
            return $hrefsrc;
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        }
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        return $basepath . 'artefact/file/download.php?file=' . $artefacts[0];
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    }

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    /**
     * Register all namespaces on an element that have been declared on the 
     * document
     *
     * TODO: we should probably do this by examining $this->namespaces
     */
    public function registerXpathNamespaces(SimpleXMLElement $element) {
        $element->registerXpathNamespace('a', PluginImportLeap::NS_ATOM);
        $element->registerXpathNamespace('rdf', PluginImportLeap::NS_RDF);
        $element->registerXpathNamespace('mahara', PluginImportLeap::NS_MAHARA);
    }

    public function get_entry_by_id($entryid) {
        static $cache = array();
        if (isset($cache[$entryid])) {
            return $cache[$entryid];
        }
        // TODO: entryid injection? Probably not worth worrying about
        $matches = $this->xml->xpath("//a:feed/a:entry/a:id[.='$entryid']/..");
        // TODO: there had better be only one...
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        if (empty($matches)) {
            return null;
        }
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        $entry = $matches[0];
        if ($entry) {
            $this->registerXpathNamespaces($entry);
        }
        return ($cache[$entryid] = $entry);
    }

    public function get_artefactids_imported_by_entryid($entryid) {
        if (!isset($this->artefactids[$entryid])) {
            return null;
        }
        return $this->artefactids[$entryid];
    }

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    public function get_viewid_imported_by_entryid($entryid) {
        if (!isset($this->viewids[$entryid])) {
            return null;
        }
        return $this->viewids[$entryid];
    }

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    /**
     * Returns xpath for an attribute matching a given curie
     *
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     * See http://wiki.cetis.ac.uk/2009-03/Leap2A_elements#Use_of_CURIEs
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     *
     * @param string $attribute The attribute to match
     * @param string $namespace The namespace for the attribute value
     * @param string $term      The term for the attribute value
     * @return string
     */
    public function curie_xpath($attribute, $namespace, $term) {
        $xpath = '';
        if (isset($this->namespaces[$namespace])) {
            $abbreviation = $this->namespaces[$namespace];

            // Simple case
            $xpath .= $attribute . '="' . $abbreviation . ':' . $term . '" or ';
            // "correct" curie syntax has them surrounded by [ ]
            $xpath .= $attribute . '="[' . $abbreviation . ':' . $term . ']" or ';
        }

        // The full URL for the curie
        $xpath .= $attribute . '="' . $namespace . $term . '"';

        return $xpath;
    }

    /**
     * Returns whether a curie matches a given namespace/term, checking all 
     * allowed forms of the curie
     *
     * @param string $curie     The curie to check
     * @param string $namespace The namespace to check the curie against
     * @param string $term      The term to check the curie against
     * @return boolean
     */
    public function curie_equals($curie, $namespace, $term) {
        if (isset($this->namespaces[$namespace])) {
            $abbreviation = $this->namespaces[$namespace];
            return
                $curie == "$abbreviation:$term"
                || $curie == "[$abbreviation:$term]"
                || $curie == $namespace . $term;
        }

        return $curie == $namespace . $term;
    }

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    /**
     * Returns whether an entry has the given RDF type
     *
     * This helper method should probably be replaced by the as yet unwritten 
     * get_rdf_type at some point, as it would be faster to get the type and do 
     * comparisons than call this multiple times.
     *
     * @param SimpleXMLElement $entry    The entry to check
     * $param PluginImportLeap $importer The importer
     * @param string $rdftype            The type to check for
     * @return boolean Whether the entry has the given RDF type
     */
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    public static function is_rdf_type(SimpleXMLElement $entry, PluginImportLeap $importer, $rdftype) {
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        $result = $entry->xpath('rdf:type['
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            . $importer->curie_xpath('@rdf:resource', $importer->get_leaptype_namespace(), $rdftype) . ']');
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        return isset($result[0]) && $result[0] instanceof SimpleXMLElement;
    }

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    /**
     * Returns if the entry has the given term in the given category
     *
     * @param SimpleXMLElement $entry    The entry to check
     * $param PluginImportLeap $importer The importer
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     * @param string $category           The category to look in. See http://wiki.cetis.ac.uk/2009-03/Leap2A_categories
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     * @param string $term               The term to look for (see the docs for the appropriate category)
     * @return boolean Whether the entry has the term in the category
     */
    public static function is_correct_category_scheme(SimpleXMLElement $entry, PluginImportLeap $importer, $category, $term) {
        $result = $entry->xpath('a:category[('
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            . $importer->curie_xpath('@scheme', $importer->get_categories_namespace(), $category . '#') . ') and @term="' . $term . '"]');
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        return isset($result[0]) && $result[0] instanceof SimpleXMLElement;
    }

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    /**
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     * Returns the <content> for a given entry, stripping off any transport 
     * encoding and respecting the content type.
     *
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     * TODO: make sure we are rawurlencoding our file paths in our export
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     *
     * @param SimpleXMLElement $entry   The entry to get the content for
     * @param PlugimImporLeap $importer The importer
     * @return string The content
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     */
    public static function get_entry_content(SimpleXMLElement $entry, PluginImportLeap $importer) {
        // Entries have content, and that content can be of different types. So we want to make sure we grab it in the right type
        // - if it's xhtml, we need asXML(), plus removing the <content> tags
        // - if it's text, what do we need???
        $type = isset($entry->content['type']) ? (string)$entry->content['type'] : 'text';
        switch ($type) {
        case 'xhtml':
            if (isset($entry->content->div)) {
                // TODO: using asXML() gives us the content, but does things 
                // like squashing the space between <br and />. This might need 
                // to be "fixed" (turned back into browser-happy xhtml) if it 
                // causes problems.
                $content = (string)$entry->content->div->asXML();
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                if (substr($content, 0, 42) == self::XHTML_DIV) {
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                    $content = substr($content, 42, -6);
                    return $content;
                }
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                else if (substr($content, 0, 43) == self::XHTML_DIV_EMPTY) {
                    return '';
                }
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            }
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            log_debug("ERROR: <content> tag for entry {$entry->id} declared to be type xhtml but didn't wrap its content in a div with xmlns=http://www.w3.org/1999/xhtml");
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            $starttaglength = strlen('<content type="xhtml">');
            $endtaglength   = strlen('</content>');
            return substr((string)$entry->content->asXML(), $starttaglength, -$endtaglength);
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        case 'html':
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        case 'text':
            return (string)$entry->content;
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        case '':
            return ''; // empty entry
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        default:
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            throw new SystemException("Unrecognised content type for entry '$entry->id' ($type)");
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        }
    }

    public static function get_entry_tags(SimpleXMLElement $entry) {
        $tags = array();
        foreach ($entry->category as $category) {
            if (!isset($category['scheme'])) {
                if (isset($category['label'])) {
                    $tags[] = (string)$category['label'];
                }
                else {
                    $tags[] = (string)$category['term'];
                }
            }
        }
        return array_unique($tags);
    }

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    /**
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     * Look for leap2:date elements that are part of an entry (if any) and 
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     * return the values we parse from them
     *
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     *
     * @param SimpleXMLElement $entry The element containing the date
     * @param array $namespaces array of namespaces @see PluginImportLeap::namespaces
     * @param string $ns namespace URL which is used as a key in the $namespaces array
     *
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     * Returned in a structure like so:
     * array(
     *     'start' => array(
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     *         'value' => 'w3c compliant date/time format, as allowed by Leap2A',
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     *         'label' => 'label attribute, which is a plaintext version of the date',
     *     ),
     *     'end' => array(
     *         'value' => 'maybe only the value is set on some elements',
     *     ),
     *     'target' => array(
     *         'label' => 'sometimes, only the label will be set'
     *     )
     * )
     *
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     * The only keys in the return value are those allowed by the Leap2A spec, 
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     * and only if they exist on the entry.
     *
     * The values may have the 'value', 'label' or both keys, depending on what 
     * each element has.
     *
     * Try and use the 'value' first, if you have a choice. Quite a few places 
     * in Mahara currently just store dates as plaintext though.
     *
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     * Spec reference: http://wiki.cetis.ac.uk/2009-03/Leap2A_literals#date
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     */
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    public static function get_leap_dates(SimpleXMLElement $entry, $namespaces, $ns) {
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        $dates = array();
        foreach (array('start', 'end', 'target') as $point) {
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            if (count($dateelement) == 1) {
                $dateelement = $dateelement[0];
            }

            if ($dateelement instanceof SimpleXMLElement) {
                $date = (string)$dateelement;
                if ($date) {
                    $dates[$point]['value'] = $date;
                }

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                // Parse for leap2:label
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                $leapattributes = array();
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                foreach ($dateelement->attributes($ns) as $key => $value) {
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                    $leapattributes[$key] = (string)$value;
                }
                if (isset($leapattributes['label'])) {
                    $dates[$point]['label'] = $leapattributes['label'];
                }
            }
        }
        return $dates;
    }

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    /**
     * Look for a leap2:myrole element that is part of an entry (if any) and
     * return the value
     *
     *
     * @param SimpleXMLElement $entry The element containing the date
     * @param array $namespaces array of namespaces @see PluginImportLeap::namespaces
     * @param string $ns namespace URL which is used as a key in the $namespaces array
     *
     * @return string
     *
     * Spec reference: http://wiki.leapspecs.org/2A/literals#myrole
     */
    public static function get_leap_myrole(SimpleXMLElement $entry, $namespaces, $ns) {
        $myrole = $entry->xpath($namespaces[$ns]