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                <?php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * Copyright (c) Andreas Heigl<[email protected]>  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * Permission is hereby granted, free of charge, to any person obtaining a copy  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * of this software and associated documentation files (the "Software"), to deal  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * in the Software without restriction, including without limitation the rights  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * copies of the Software, and to permit persons to whom the Software is  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * furnished to do so, subject to the following conditions:  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * The above copyright notice and this permission notice shall be included in  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * all copies or substantial portions of the Software.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * THE SOFTWARE.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @author    Andreas Heigl<[email protected]>  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @copyright Andreas Heigl  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @license   http://www.opensource.org/licenses/mit-license.php MIT-License  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @since     29.07.2016  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @link      http://github.com/heiglandreas/callingallpapers  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                namespace Callingallpapers\Parser;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Callingallpapers\Parser\PapercallIo\EventParser;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Callingallpapers\Service\TimezoneService;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Callingallpapers\Writer\WriterInterface;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use DOMDocument;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use DOMXPath;  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                class PapercallIoParser implements ParserInterface  | 
            
            
                                                                        
                            
            
                                    
            
            
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                { | 
            
            
                                                                        
                            
            
                                    
            
            
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                    const SOURCE = 'papercallio';  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    protected $tzService;  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    private $uri = 'https://papercall.io/cfps?page=%1$s';  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    private $parser;  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function __construct(TimezoneService $tzService, EventParser $parser)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $this->tzService = $tzService;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $this->parser = $parser;  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function setStartUrl(string $uri)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $this->uri = $uri;  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function parse(WriterInterface $writer)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $i = 0;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $pages = null;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        do { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $dom = new DOMDocument('1.0', 'UTF-8'); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            libxml_use_internal_errors(true);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $uri = sprintf($this->uri, $i+1);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $dom->loadHTMLFile($uri);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            libxml_use_internal_errors(false);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $dom->preserveWhiteSpace = false;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $xpath = new DOMXPath($dom);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            if (null === $pages) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                $p = $xpath->query("//ul[contains(@class,'pagination')]/li"); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                $pages = $p->length - 2;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $nodes = $xpath->query("//div[contains(@class,'main')]/div[@class='container'][2]//div[@class='box']"); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            if ($nodes->length < 1) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                continue;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            /** @var DOMNode $node */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            foreach ($nodes as $node) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                try { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                    $writer->write($this->parser->parseEvent($node), self::SOURCE);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                } catch (\Exception $e) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                    error_log($e->getMEssage());  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        } while (++$i < $pages);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return true;  | 
            
                            
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                    }  | 
            
            
                                                        
            
                                    
            
            
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                }  | 
            
            
                                                        
            
                                    
            
            
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_functionexpects aPostobject, and outputs the author of the post. The base classPostreturns a simple string and outputting a simple string will work just fine. However, the child classBlogPostwhich is a sub-type ofPostinstead decided to return anobject, and is therefore violating the SOLID principles. If aBlogPostwere passed tomy_function, PHP would not complain, but ultimately fail when executing thestrtouppercall in its body.