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1<?php
2
3/**
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; under version 2
7 * of the License (non-upgradable).
8 *
9 * This program 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 this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
17 *
18 * Copyright (c) 2014 (original work) Open Assessment Technologies SA;
19 *
20 *
21 */
22
23/**
24 * Iterates over the resources of classes
25 *
26 * @author Joel Bout <joel@taotesting.com>
27 */
28class core_kernel_classes_ResourceIterator implements \Iterator
29{
30    public const CACHE_SIZE = 100;
31
32    private $classIterator;
33
34    /**
35     * Id of the current instance
36     *
37     * @var int
38     */
39    private $currentInstance = 0;
40
41    /**
42     * List of resource uris currently being iterated over
43     *
44     * @var array
45     */
46    private $instanceCache = null;
47
48    /**
49     * Indicator whenever the end of  the current cache is also the end of the current class
50     *
51     * @var boolean
52     */
53    private $endOfClass = false;
54
55    /**
56     * Whenever we already moved the pointer, used to prevent unnecessary rewinds
57     *
58     * @var boolean
59     */
60    private $unmoved = true;
61
62    /**
63     * Constructor of the iterator expecting a class or classes as argument
64     *
65     * @param mixed $classes array/instance of class(es) to iterate over
66     */
67    public function __construct($classes)
68    {
69        $this->classIterator = new core_kernel_classes_ClassIterator($classes);
70    }
71
72    /**
73     * (non-PHPdoc)
74     * @see Iterator::rewind()
75     */
76    public function rewind()
77    {
78        if (!$this->unmoved) {
79            $this->classIterator->rewind();
80            $this->ensureNotEmpty();
81            $this->unmoved = true;
82        }
83    }
84
85    /**
86     * @return core_kernel_classes_Resource|null
87     * @throws common_exception_Error
88     */
89    public function current()
90    {
91        if ($this->instanceCache === null) {
92            $this->ensureNotEmpty();
93        }
94
95        return isset($this->instanceCache[$this->currentInstance]) ?
96            new \core_kernel_classes_Resource($this->instanceCache[$this->currentInstance]) :
97            null;
98    }
99
100    /**
101     * (non-PHPdoc)
102     * @see Iterator::key()
103     */
104    public function key()
105    {
106        return $this->classIterator->key() . '#' . $this->currentInstance;
107    }
108
109    /**
110     * (non-PHPdoc)
111     * @see Iterator::next()
112     */
113    public function next()
114    {
115        $this->unmoved = false;
116        if ($this->valid()) {
117            $this->currentInstance++;
118            if (!isset($this->instanceCache[$this->currentInstance])) {
119                // try to load next block (unless we know it's empty)
120                $remainingInstances = !$this->endOfClass
121                    && $this->load($this->classIterator->current(), $this->currentInstance);
122
123                // endOfClass or failed loading
124                if (!$remainingInstances) {
125                    $this->classIterator->next();
126                    $this->ensureNotEmpty();
127                }
128            }
129        }
130    }
131
132    /**
133     * While there are remaining classes there are instances to load
134     *
135     * (non-PHPdoc)
136     * @see Iterator::valid()
137     */
138    public function valid()
139    {
140        if ($this->instanceCache === null) {
141            $this->ensureNotEmpty();
142        }
143        return $this->classIterator->valid();
144    }
145
146    // Helpers
147
148    /**
149     * Ensure the class iterator is pointin to a non empty class
150     * Loads the first resource block to test this
151     */
152    protected function ensureNotEmpty()
153    {
154        $this->currentInstance = 0;
155        while ($this->classIterator->valid() && !$this->load($this->classIterator->current(), 0)) {
156            $this->classIterator->next();
157        }
158    }
159
160    /**
161     * Load instances into cache
162     *
163     * @param core_kernel_classes_Class $class
164     * @param int $offset
165     * @return boolean
166     */
167    protected function load(core_kernel_classes_Class $class, $offset)
168    {
169        $results = $this->loadResources($class, $offset);
170        $this->instanceCache = [];
171        foreach ($results as $resource) {
172            $this->instanceCache[$offset] = $resource->getUri();
173            $offset++;
174        }
175
176        $this->endOfClass = count($results) < self::CACHE_SIZE;
177
178        return count($results) > 0;
179    }
180
181    /**
182     * Load resources from storage
183     *
184     * @param core_kernel_classes_Class $class
185     * @param integer $offset
186     * @return core_kernel_classes_Resource[]
187     */
188    protected function loadResources(core_kernel_classes_Class $class, $offset)
189    {
190        return $class->searchInstances([], [
191            'recursive' => false,
192            'limit' => self::CACHE_SIZE,
193            'offset' => $offset,
194        ]);
195    }
196}