src/Util/ReversedFileReader.php

   1 <?php
   2 /**
   3  * @copyright Copyright (C) 2021, Friendica
   4  *
   5  * @license GNU AGPL version 3 or any later version
   6  *
   7  * This program is free software: you can redistribute it and/or modify
   8  * it under the terms of the GNU Affero General Public License as
   9  * published by the Free Software Foundation, either version 3 of the
  10  * License, or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU Affero General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Affero General Public License
  18  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  19  *
  20  */
  21
  22 namespace Friendica\Util;
  23
  24 /**
  25  * An iterator which returns lines from file in reversed order
  26  *
  27  * original code https://stackoverflow.com/a/10494801
  28  */
  29 class ReversedFileReader implements \Iterator
  30 {
  31         const BUFFER_SIZE = 4096;
  32         const SEPARATOR   = "\n";
  33
  34         /** @var int */
  35         private $filesize;
  36
  37         /** @var int */
  38         private $pos;
  39
  40         /** @var array */
  41         private $buffer;
  42
  43         /** @var int */
  44         private $key;
  45
  46         /** @var string */
  47         private $value;
  48
  49         public function __construct($filename)
  50         {
  51                 $this->_fh = fopen($filename, 'r');
  52                 if (!$this->_fh) {
  53                         // this should use a custom exception.
  54                         throw \Exception("Unable to open $filename");
  55                 }
  56                 $this->filesize = filesize($filename);
  57                 $this->pos      = -1;
  58                 $this->buffer   = null;
  59                 $this->key      = -1;
  60                 $this->value    = null;
  61         }
  62
  63         public function _read($size)
  64         {
  65                 $this->pos -= $size;
  66                 fseek($this->_fh, $this->pos);
  67                 return fread($this->_fh, $size);
  68         }
  69
  70         public function _readline()
  71         {
  72                 $buffer = & $this->buffer;
  73                 while (true) {
  74                         if ($this->pos == 0) {
  75                                 return array_pop($buffer);
  76                         }
  77                         if (count($buffer) > 1) {
  78                                 return array_pop($buffer);
  79                         }
  80                         $buffer = explode(self::SEPARATOR, $this->_read(self::BUFFER_SIZE) . $buffer[0]);
  81                 }
  82         }
  83
  84         public function next()
  85         {
  86                 ++$this->key;
  87                 $this->value = $this->_readline();
  88         }
  89
  90         public function rewind()
  91         {
  92                 if ($this->filesize > 0) {
  93                         $this->pos    = $this->filesize;
  94                         $this->value  = null;
  95                         $this->key    = -1;
  96                         $this->buffer = explode(self::SEPARATOR, $this->_read($this->filesize % self::BUFFER_SIZE ?: self::BUFFER_SIZE));
  97                         $this->next();
  98                 }
  99         }
 100
 101         public function key()
 102         {
 103                 return $this->key;
 104         }
 105
 106         public function current()
 107         {
 108                 return $this->value;
 109         }
 110
 111         public function valid()
 112         {
 113                 return ! is_null($this->value);
 114         }
 115 }