app/Beat/Encoder.php

   1 <?php
   2
   3 namespace App\Beat;
   4
   5 class Encoder {
   6
   7         public function __construct($source) {
   8                 $this->source = $source;
   9         }
  10
  11         public function createPatch($target, $metadata = '') {
  12                 $this->target = $target;
  13                 $this->patch = '';
  14                 $this->sourceCursor = 0;
  15                 $this->targetCursor = 0;
  16
  17                 $this->writeString('BPS1');
  18                 $this->writeNumber(strlen($this->source));
  19                 $this->writeNumber(strlen($this->target));
  20                 $this->writeNumber(strlen($metadata));
  21                 $this->writeString($metadata);
  22
  23                 $lastKnownChange = 0;
  24                 $targetCopyPos = 0;
  25                 while ($this->targetCursor < strlen($this->target)) {
  26                         $numUnchanged = 0;
  27                         while ($this->sourceLeft($numUnchanged) && $this->sourceEqual($numUnchanged, $numUnchanged, 1)) {
  28                                 ++$numUnchanged;
  29                         }
  30                         if ($numUnchanged > 1 || $numUnchanged == (strlen($this->target) - $this->targetCursor)) {
  31                                 $this->writeNumber(($numUnchanged - 1) << 2);
  32                                 $this->sourceCursor += $numUnchanged;
  33                                 $this->targetCursor += $numUnchanged;
  34                         }
  35
  36                         $numChanged = 0;
  37                         if ($lastKnownChange > $this->targetCursor) {
  38                                 $numChanged = $lastKnownChange - $this->targetCursor;
  39                         }
  40                         while ((!$this->sourceLeft($numChanged) || !$this->sourceEqual($numChanged, $numChanged, 3))
  41                                 && $this->targetLeft($numChanged)
  42                         ) {
  43                                 ++$numChanged;
  44                                 if (!$this->sourceLeft($numChanged)) {
  45                                         $numChanged = strlen($this->target) - $this->targetCursor;
  46                                 }
  47                         }
  48                         $lastKnownChange = $this->targetCursor + $numChanged;
  49                         if ($numChanged) {
  50                                 $rle1Start = $this->targetCursor == 0 ? 1 : 0;
  51                                 while (true) {
  52                                         if ($this->targetEqual($rle1Start - 1, $rle1Start, 4)
  53                                                 || $this->targetEqual($rle1Start - 2, $rle1Start, 5)
  54                                         ) {
  55                                                 $numChanged = $rle1Start;
  56                                                 break;
  57                                         }
  58                                         if ($rle1Start + 3 > $numChanged) {
  59                                                 break;
  60                                         }
  61                                         ++$rle1Start;
  62                                 }
  63                                 if ($numChanged) {
  64                                         $this->writeNumber(($numChanged - 1) << 2 | 1);
  65                                         $this->writeString(substr($this->target, $this->targetCursor, $numChanged));
  66                                         $this->sourceCursor += $numChanged;
  67                                         $this->targetCursor += $numChanged;
  68                                 }
  69                                 if ($this->targetEqual(-2, 0, 3)) {
  70                                         $rleLen = 0;
  71                                         while ($this->targetLeft($rleLen) && $this->targetEqual(0, $rleLen, 2)) {
  72                                                 $rleLen += 2;
  73                                         }
  74                                         $this->writeNumber(($rleLen - 1) << 2 | 3);
  75                                         $this->writeNumber(($this->targetCursor - $targetCopyPos - 2) << 1);
  76                                         $this->sourceCursor += $rleLen;
  77                                         $this->targetCursor += $rleLen;
  78                                         $targetCopyPos = $this->targetCursor - 2;
  79                                 } else if ($this->targetEqual(-1, 0, 2)) {
  80                                         $rleLen = 0;
  81                                         while ($this->targetLeft($rleLen) && $this->targetEqual(0, $rleLen, 1)) {
  82                                                 $rleLen += 1;
  83                                         }
  84                                         $this->writeNumber(($rleLen - 1) << 2 | 3);
  85                                         $this->writeNumber(($this->targetCursor - $targetCopyPos - 1) << 1);
  86                                         $this->sourceCursor += $rleLen;
  87                                         $this->targetCursor += $rleLen;
  88                                         $targetCopyPos = $this->targetCursor - 1;
  89                                 }
  90                         }
  91                 }
  92
  93                 $this->write32(crc32($this->source));
  94                 $this->write32(crc32($this->target));
  95                 $this->write32(crc32($this->patch));
  96
  97                 return $this->patch;
  98         }
  99
 100
 101         private function sourceChar($offset = 0) {
 102                 return $this->source[$this->sourceCursor + $offset];
 103         }
 104
 105         private function sourceEqual($aOff, $bOff, $len) {
 106                 $aStr = substr($this->source, $this->sourceCursor + $aOff, $len);
 107                 $bStr = substr($this->target, $this->targetCursor + $bOff, $len);
 108                 return $aStr == $bStr;
 109         }
 110
 111         private function sourceLeft($num) {
 112                 return $this->sourceCursor + $num < strlen($this->source);
 113         }
 114
 115         private function targetChar($offset = 0) {
 116                 return $this->target[$this->targetCursor + $offset];
 117         }
 118
 119         private function targetEqual($aOff, $bOff, $len) {
 120                 $aStr = substr($this->target, $this->targetCursor + $aOff, $len);
 121                 $bStr = substr($this->target, $this->targetCursor + $bOff, $len);
 122                 return $aStr == $bStr;
 123         }
 124
 125         private function targetLeft($num) {
 126                 return $this->targetCursor + $num < strlen($this->target);
 127         }
 128
 129
 130         private function write32($val) {
 131                 $this->writeByte($val & 0xFF);
 132                 $this->writeByte(($val >> 8) & 0xFF);
 133                 $this->writeByte(($val >> 16) & 0xFF);
 134                 $this->writeByte(($val >> 24) & 0xFF);
 135         }
 136
 137         private function writeByte($val) {
 138                 $this->patch .= chr($val);
 139         }
 140
 141         private function writeNumber($val) {
 142                 $tmpval = $val;
 143                 for ($i = 0; $i < 16; ++$i) {
 144                         $tmpbyte = $tmpval & 0x7f;
 145                         $tmpval >>= 7;
 146                         if (!$tmpval) {
 147                                 $this->writeByte($tmpbyte | 0x80);
 148                                 break;
 149                         }
 150                         $this->writeByte($tmpbyte);
 151                         --$tmpval;
 152                 }
 153         }
 154
 155         private function writeString($str) {
 156                 $this->patch .= $str;
 157         }
 158
 159
 160         private $source;
 161         private $target = '';
 162         private $patch = '';
 163
 164         private $sourceCursor = 0;
 165         private $targetCursor = 0;
 166
 167 }